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Oconee, Units 1, 2, and 3 - Validation of Hrr Breach Hydrograph for Jocassee Dam, Dated April 30, 2014 (Redacted)
	ML16272A216
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Site:	Oconee
Issue date:	04/30/2014
From:	Ehasz J L; URS Corp
To:	; Office of Nuclear Reactor Regulation
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Enclosure IML14139A175* lthkkh.Id ,fr,,m i,lkl. 4( Enclosure 1Validation of HRR Breach Hydro graph for Jocassee Damby Joseph L. Ehasz, P.E. andDr. David S., Bowles, P.E.,April 2014 WgVALIDATION OF HRRBREACHHYDROGRAPH FORJOCASSEE DAM(Through an In-Depth Review of the Xu and Z[hangBreach Parameter Estimation Methodology)April 2014ByJoseph 1. Ehasz, P.E.Dr. David S. Bowles, P.E.~~~~~~1~~

-. A -------------TL1--------URSIn assodiation with VALIDATION OF HRR BREACH HYDROGRAPH FOR JOCASSEE DAMA"Jr" ............. VALIDATION OF HRR BREACH HYDROGRAPH FOR JOCASSEE DAMVALIDATION OF HRR BREACH HYDROGRAPH FOR JOCASSEE DAM(THROUGH AN IN-DEPTH REVIEW OF THE XU AND ZHANG BREACH PARAMETER ESTIMATIONMETHODOLOGY)APRIL 2014BYAPRIL 30, 2014JOSEPH L. EHASZ, P.E.URS CIVIL CONSTRUCTION & MINING, INC.DR. DAVID.S. BOWLES, P.E.RAC ENGINEERS AND ECONOMISTS, LLCAPRIL 30,A201PAGE I oerurn~y ,nrormuuon -wIUmnoIU rrom puo~uC asciosure per 1u L1-I 2,390(c1)VALIDATION OF HRR BREACH H VDROGRAPH FOR JOCASSEE DAMTABLE OF CONTENTSSECTION PAGE1.0 OBJECTIVE ..................................................................................................... 11.1 Authorization .................................................................................................. 11.2 Objective of the Validation Report............................................................................

12.0 INTRODUCTION

................................................................................................ 22.1 HRR (Duke 2013) Breach Hydrograph ....................................................................... 22.2 Agency Questions ............................................................................................ 32.3 Summary of Approach for This Review ...................................................................... 42.4 Report Ouline ................................................................................................ 53.0 BACKGROUND ................................................................................................. 73.1 Characterization of Jocassee Dam ........................................................................... 73.2 Piping Failure Mechanism .................................................................................... 93.3 Potential Piping Failure Modes for Jocassee Dam.......................................................... 104.0 CONFIRMATION OF JOCASSEE DAM ERODIBILITY....................................................... 114.1 Overview..................................................................................................... 114.2 Use of Briaud's Erosion Categorization Scheme by Xu and Zhang (2009)................................. 114.3 Confirmation of Low Erosion Category for Jocassee Dam.................................................. 135.0 ORIGINAL XU AND ZHANG REGRESSION EQUAlIONS................................................... 156.0 REVIEW AND REVISION OF XU AND ZHANG REGRESSION EQUATIONS............................... 166.1 Approach to Review and Revision .......................................................................... 166.2 Summary of Review Findings................................................................................ 176.3 Summary of Revisions to Case History Data Set........................................................... 246.4 Revised Regression Equations for use in the Sensitivity Study .........................................,.,.266.5 Application to Teton Dam Failure ........................................................................... 281.0 REVISED XU AND ZHANG REGRESSION EQUATIONS SENSITIVITY STUDIES ......................... 327.1 Overview of Approach....................................................................................... 327.2 Revised Xu and Zhang Breach Parameter Estimates for Jocassee Dam .................................. 327.3 Example of Inconsistencies between Peak Breach Flow and Breach Development Time ................. 407.4 Discussion of HEC-RAS Results..... ....................................................................... 4

18.0 CONCLUSION

S ............................................................................................... 458.1 Discuss Overall Conclusion ................................................................................. 458.2 Concluding Responses to Agency Questions............................................................... 458.3 Concluding Support for the HRR Breach Hydrograph ...................................................... 4

69.0 REFERENCES

................................................................................................. 50PA GE ii s.,onrans minrirwuun [lEE pua; uo ,uou r x I.r 3 83,VALIDA TION OF HRR BREACH HYDROGRAPH FOR JOCASSEE, DAM.p_APPENDICESAppendix A- B riaud's ReportAppendix B -Original Xu and Zhang Regression Equations and HRR Hydrograph.Appendix C -Bench Marking / Comparative Analysis0. 1 -Benchmarking Rockfill Dams and Failures0.2- Embankment DesignAppendix D -Detailed Data Supporting Xu and Zhang RevisionsAppendix E -Mark Morris Review ReportP A GE iii VALIDATION OF HRR BREACH HYDROGRAPH FOR JOCASSEE DAM1.0 OBJECTIVE1.1 AuthorizationThe authorization for this review was attached in an e-mail dated June 20, 2013 from Mr. DeanHubbard, Duke Energy, to Mr. Joseph Ehasz, URS, Civil Construction & Mining1.2 Objective of the Validation ReportThe objective of this report is to respond to questions raised by the FERC and the NRC aboutthe use of the Xu and Zhang (2009) regression equations for estimating breach parameters todevelop the breach hydrograph for a deterministic sunny-day breach of the Jocassee Dam. Theagency questions are presented in Section 2.2. The implications of these responses and adetailed review of the Xu and Zhang (2009) methodology provide support for the breachhydrograph submitted to the NR C by Duke (2013) in the Hydrologic Reevaluation Report (HRR).PAGE 1 VALIDATION OF HRR BREACH HYDROGRAPH FOR JOCASSEE DAM

2.0 INTRODUCTION

2.1 HRR (Duke 2013) Breach HydrographThe HRR breach hydrographs (DUKe 2013) for a deterministic :sunny-day breach of theJocassee Dam were developed as follows:*The predicted median breach dimensions obtained from the Xu and Zhang (2009) bestexact regression equations for a low erosion category were input to the HEC-RASmodel.*The values of the orifice and weir" coefficients and the breach progression relationship inHEC-RAS were iteratively changed within reasonable ranges of values to match thepredicted peak breach flow rate and the failure time from Xu and Zhang (2009).Consistent with the definition of failure time by Xu and Zhang (2009), the predicted valueof failure time was used in HEC-RAS as a combination of breach initiation and breachformation.An independent review, entitled "Jocassee and Keowee Dams Breach Parameter Review",dated February 2013, was performed on the Jocassee Dam postulated breach parameterestimates and underlying assumptions by Joseph L. Ehasz and Dr. David S. Bowles (Ehasz andBowles 2013). That review focused on the appropriateness of estimating potenti~al pipingbreach parameters for the Jocassee Dam based on the rXu and Zhang (2009) regressionequations. Duke Energy and its consultant HDR Engineering had selected the dam breachparameter estimation methodology proposed by Y. Xu and L. M. Zhang in their technical paperentitled "Breaching Parameters for Earth and Rockfill Dams" published in the American Societyof Civil Engineers (ASCE) Journal of Geotechnical and Geoenvironmental Engineering inDecember 2009 and in Xu (2010). This is a "state of knowledge" paper and is specificallyapplicable for consideration of a piping breach in a zoned embankment dam. The .mainobjective of the paper is to develop robUst empirical formulas for estimating dam breach'parameters that consider ph~ysical characteristics of the dam such as the erodibility of theembankment materials in addition to the dam height and reservoir volume, which most otherregression methods rely on.The physical features of embankment dam design and construction Strongly influence both the.likelihood of a piping dam breach occurring and the breach characteristics in the event that abreach occurs. Therefore, our February 2013 report (Ehasz and Bowles 2013) began with asummary of some important physical features of the Jocassee Dam. It continued with anevaluation of, if piping should initiate, would detection. and Successful intervention be likely toprevent a failure. It discussed what piping failure modes might apply to Jocassee Dam basedon a potential failure modes analysis and some general breach parameter PAGE 2

~J S In association with lAhCVALIDATION OF HRR BREACH HYDROGRAPH FOR JOCASSEE DAMFinally, it evaluated, using the "state of knowledge," what are the appropriate breach param etersfor Jocassee Dam? Those parameters were then used by HDR to simulate the downstreamconditions that mi;ght result from a breach of Jocassee Dam caused by a piping failure.The basis of the breach parameters that were used to represent the Jocassee Dam for a pipingbreach and the resulting breach hydrograph were developed based on the breach parameterestimation methodology developed by Xu and Zhang (2009). Significant factors in selecting theXu and Zhang (2009) methodology 'included its distinction between modes of failure, namelyeither overtopping or piping, and its consideration of the erodibility of the embankmentmaterials. In fact, erodibility was found to be the most significant control variable in the Xu andZhang (2009) regression equations for all five breach parameters.The conclusions from our February 2013 (Ehasz and Bowles 2013) review of 'the basiS for theHRR breach hydrograph (Duke 201.3) are sum marized as follows:,Xu and Zhang (2009) is considered to be a "state-of-the~practice" regression method forestimating .piping dam breach parameters. Unlike most other methods,, it includeserodibiiity as .a control variable. This. variable was found to be the most .importantvariable in. the Xu and Zhang (2009) regression analysis. The capability to considererodibility is particularly important for predicting breach parameters for Jocassee Dam toaccount for the influence of its modern dense rockfill construction.*The HRR (Duke 2013) breach hydrograph is .a realistic but conservative breachhydrograph that, has good defendablity based on the validity of the Xu and Zhanig (2009)method and the conservative nature of the median br~each parameter estimates due to:o uni-directional breach formation due a postulated piping failure mode initiating inthe o the deposition of eroded rockflll immediately below the dam leading to a tailwaterrise that would limit the rate of breach development: ando the robust characteristics of a modern zoned central core rockfill dam that wereincluded in the design and construction of Jocassee Dam that make it moreerosion resistant than other low erodibility dams in the Xu and Zhang (2009) casehistories data set on which their regression analysis is based.2.2 Agency Questions'PresentationS of the estimated Jocassee Dam breach parameters and simulated downstreamconditions were made to both the FERC and the NRC based on the review presented in ourFebruary 2013 report (Ehasz and Bowles 2013). In ,addition,. a field trip was made to theJocassee Dam site by representatives of both regulatory agencies to visually inspect, thecondition of the dam as-well as the monitoring procedures .and resulting observations.PAGE 3 5------- -----U-,BpVlll rIFVl #VJ VAUDATION OF HRR BREACH HYDROGRAPH FOR JOCASSEE DAMBoth the FERC and the NRC had questions about the use of the Xu and Zhang (2009)methodology fordeveloping the breach parameter estimates. These questions are summarizedas follows:1) Precedence -where has use of the Xu and Zha ng (2009) methodology been accepted?2) Chinese case histories -about 43% of the dam failure case histories on which the Xuand Zhang (2009) methodology is based are Chinese dams for which littleinformation is available in the US.3) Representation of icase histories for rockfill and other low erodibility dams -thedata set of dams used by Xu and Zhang (2009) to develop ,the regression equations hasonly three dams that are considered large (iLe. > 15 meters high) embankment damswith low erodibility and these darms are all outside of the US.,4) Use of the Briaud erosion categories -how were the erosion categories developed byBriaud (2008) applied in develOping the Xu and Zhang (2009) methodology and are theyapplicable to dam breach?5) Breach time definition1 -the definition of time to failure used by XU and Zhang (2009)includes at least part of the breach initiation phase in addition to the breach formationprocess unlike other regression methods that include only the breach formation process.Therefore the objective of this report is to respond to these agency questions and to providesupport for the appropriate use of the Xu and Zhang (2009) methodology for Jocassee Dam indeveloping the HRR breach hydrograph submitted to the NRC by Duke. (201 3).2.3 Summary of Approach for This ReviewThe- major activities conducted under this review were as follows:*A four-day working session was held with Dr. Yao Xur, the principal author of the Xu andZhang (2009) methodology. Professor Jean-Louis Briaud, the author of the erosioncategorization methodology used by Xu and Zhang (2009) participated in the first twodays. Dr. Xu responded to the agencY questions, and participated in a detailed case-by-case review of the 75 case histories that were used to develop the Xu and Zhang (20,09)regression equations.* Professor Briaud made a site visit to Jocassee Dam to become familiar with theproperties of the rockfill materialr and other aspects of its cOnstruction. He addressedquestions ,regarding the appropriateness of using his erosion categorizationmethodology in the Xu and Zhang (2009) breach parameter methodology. He alsoconfirmed the low erosion category for Jocassee Dam.'-in this report-the terms breach development time, and breach formation time are used interchangeably.PAGE 4 IJSIn association with VALIDATION OF HRR BRF.ACH HYDROGRAPH FOR JOCA SSEE DAMpRevised regression equations were developed by Dr. Xu for sensitivity studies on theJocassee Dam HRR breach hydrograph based on changes that were made to theoriginal Xu and Zhang (2009) case histories data set to address the agency questionsand some other issues identified during our detailed review. The revised equations werealso applied to Teton Dam to compare with the observed breach parameters and thoseobtained by Xu and Zhang (2009) an d the observed breach parameters.*Sensitivity studies were conducted based on the revised Xu and Zhang and theFroehlich (1995a and 2008) regression equations applied to Jocassee Dam. Theresulting breach parameter estimates were used by HDR in the HEC-RAS model toobtain breach hydrographs .for a deterministic sunny-day breach of the Jocassee Dam.A comparison of these hydrographs with the HRR breach hydrograph submitted to theNRC by Duke (2013) provided support for the HRR breach hydrograph.2.4 Report Outline* Section 3 of this rePOrt contains an update of the background discussion of JocasseeDam that was provided in our February 2013 report (Ehasz and Bowles 2013).* Section 4 presents the outcomes of Professor Briaud's visit to Jocassee Dam hisconfirmation of the low erosion category for the rockfill material for this dam.* Section 5 refers to a summary of the original Xu and Zhang. (2009) methodology and itsoriginal implementation for Jocassee Dam contained in Appendix B.* Section 6 presents the findings of the review of the original Xu and Zhang (2009)methodology that we conducted with Dr. Xu, including the changes made to the casehistories data set to address the FERC and NRC questions and the development ofrevised regression equations.* Section 7 presents the sensitivity study using the revised regression equations forJocassee Dam, which .prOvides support for the breach hydrographs submitted in theHydrologic Reevaluation Report (HRR) to the NRC by Duke on March, 12, 201i3 (Duke2013).* Section 8 presents the overall conclusions and responds to the questions presented bythe FERO and NRC.* Appendix A contains Professor Briaud's complete report.* Appendix B. summarizes the original Xu and Zhang (2009) methOdology and its originalimplementation for Jocassee Dam on which the HRR hydrograph (Duke 2013) is based.* Appendix C contains a bench marking/comparative analysis for rockfiUl dams andcharacteristics of recent failures relative to Jocass ee Dam.* Appendix D contains the detailed data supporting the revision to the Xu and Zhangregression equations.PAGE 5 TI "R In association with CVALIDATION OF HRR BREACH HYDROGRAPH FOR JOCASSEE DAMAppendix E contains a review of this report ,by Dr. Mark Morris, an internationallyrecognized European expert in dam breach analysis and breach hydrographdevelopment.The most significant outcome and conclusions of this report are the verification and revision ofthe data set utilized to develop the breach parameter regression equations presented in the Xuand Zhang (2009) and the verification of the interpretation of the erosion characteristics onwhich the Xu and Zhang (2009) methodology is based. Through sensitivity analyses based onthe revised Xu and Zhang regression equations and the Froehlich (1995a and 2008) regressionequations it is demonstrated that the HRR .breach hydrograph (Duke.2013) for a deterministicsunny-day piping breach of the Jocassee Dam is a reasonable and contservative estimate.PAGE 6,

~1MIENprn ~in.A5I 58W ~mIW85VW 5155121 UIIEII.MI -WWIIRIINU.MI.Z 11(2115 £51R82158. LumqU3ala, W 5(2 I..r~ £..I~m CII....... dV.............................. ............... ............. i,,.-7VAUDA 170ff Of HRR BREACH HYRGRP FOR JOCASSEE DAM3.0 BACKGROUNDOur February 2013 (Ehasz and Bowles 2013) report gave some details of the Jocassee Damembankment, the general piping failure mechanism and the potential piping failure modes forthe dam. As background and for continuity, this report will repeat some of this information inthis section, especially with regard to the characterization of the dam and it's attributes as theyaffect erodibility during development of a postulated breach.3.1 Characterization of Jocassee DamThe following statements describe the detailed characteristics of the dam and are significant todam performance and breach characteristics (see Figures 3.1 and 3.2):* The dam was completed in 1967. It has been continuously monitored and hasperformed very well to the present; meeting or exceeding FERO standards. Eventhough the dam was designed and constructed in the mld-1960's it has all the modemand defensive measures of the rockfill dams designed and constructed today. A detailedreview of the Jocassee Dam and it's performance was conducted 20 years aftercompletio as described in the report entitled, "Jocassee Main Dam Design,Construction and Performance", by George F. Sowers, April 1987.Figure 3.1. Google aerial view of Jocassee DamPAGE 7

..... .f.. ... .. ..i'L ......1 j F E' S Q.% .1 -,In association with R .I LCff -- 7rEVALIDATION OF HRR BREACH H'YDROGRAPH FOR JOCA$$EE DAMU(b)(7)(F)~~JOCASf.;E PAM s~cri0NFigure 3.2. Jocassee Dam cross section (Sowers 1987)Security sensitive Information. Withhold from public disclosure under 10 CFR 2.390 (d)( 1)Beginning at the rock foundation levelI,(b)(l)F) I0(b)(7)(F)v r iTo decrease the hydraulic as low as possible (b)(7)(F)vPAGE 8.l along thefoundation contact.To protect the core materials from internal erosion, material movement and potentialpiping of the core, I(b)(7)(F)(b)(7)(F)linto the larger rockfill materials.PAGES I':z.. *.sz.. -.:..:.. --- ;iI.2 ..ll~l .Sm.l Ua,.~pgjLajr-i a Uaw --U L-r" -.. .......KJDgS Insocaonwt1A C* VALIDATION OF HRR BREACH HYVDROGRA PH FOR JOCASSEE DAMQuality Control: selection of materials and documentation was enforced by the ResidentEngineering staff and maintained as an. important function during .the construction.' Asindicated above, the selection and placement of the various Zones was carefully done soas 'to maintain 'the' compatibility'of adjacent materials-to eliminate migration of materialsand maintain a stable embankment. Grain-size and density testing .to verify selection ofsoil. and rockfill materials properties and' compaction were condUcted .at intervals tOconfirm and maintain control of the placements. Field inspection was maintained duringconstruction with Duke Engineering staff observing and. interfacing to ensure the intent was maintained throughout construction.All Of the above facts are important when considering the potential for internal erosion andpiping at Jocassee Dam. The materials and features employed during design and construction,.as described above, were all-designed to minimize the possibility of piping .and .failure of theembankment. Thus, it is even difficult to .envision the development of a piping condition .at theJocassee Dam, given the defensive design measures incorporated and with the past 45 yearsof excellent performance. However, a deterministic approach is being .used to postulate asunny-day piping failure for Jocassee Dam,Many of the above-listed facts .also affect the. breaching, characteristics Under the hypothesisthat. a .piping failure occurs. Ideally these favorable physical properties would be taken intoconsideration in estimating breach parameters. Unfortunately regression methods forestimating breach parameters are .somewhat limited .in the. degree ,to which this can be done.An exception is the Xu and Zhang (2009) methodology in which erodibility is considered.3.2 Piping Failure MechanismFor piping to occur, all four of the following Conditions, must exist:1) there must be a source of water and a flow path;2) there must be an unprotected exit for the eroded material;3) there must be. erodible, material in the flow path'; and4) the material must .support a roof for a pipe to enlarge and .propagate.The piping phenomenon must originate with internal erosion and material movement'somewhere within the dam or its foundation, such .as at the abutment-core contact, and exitdownstream. The flow of water and materials must have an exit, to which the flow can carrymatedials and then progress upstream along some erosion path. and move mat~erials fromluPAGE 9 I.n ~ , wrny .O~aev Ir, ,, ,u u ;;-, vv;ui,. i ,-, 'pu,Ij... ......... .... .-93KIR In association wath~ ' * ' VAL.IDATION OF HRR BREACH HYDROGRAPH FOR JOCASSEE DAM*upstream. With 'increasing movement of large amounts of water carrying materials, the flow.would eventually form a flow path within the downstream rockfili portiOn of'the dam, referred toas a "pe". If the process, called the "breach initiation phase", continues and the flowsincrease, it would .progressively engage a larger and larger portion of the rockfill and eventuallyform a raveling Condition within the rockfillt large enough to make the downstream shell of thedam unstable. If it becomes unstable enough to move. rockfill downstream *or to cause pocketsthrough Collapses, it could then expose the core, which is the water retaining structure of thedam for the upstream reservoir. If support is removed from the downstream side of the core, itwould become unstable and partially collapse. The breach of the dam would progress as itovertops the core and form an overtopping breach and failure of the dam; this is Considered the>Start of the "breach formation phase".The defensive measures within the Jocassee Dam are designed, constructed and incorporated,with consideration of all four of the necessary conditions for piping, to minimize any potential forthe piping process to occur.3.3 Potential Piping Failure Modes for Jocassee DarnIn a Potential Failure Modes Analysis (PFMA), which was facilitated by RAC Engineers &Economists and' included engineers from.Duke Hydro and HDR,. mn-t Iik.lv unlikely") pipingl failure mode was determined tobe' piping; I(I()()PiPing through the rock foundation of the main dam is considered*to be a Significantly less lkely piing failure mode due to the tight rock formations and lowseepage rates in the I~b()(F) j The po~tential for piping through the main dam embankmentis extremely Unlikely for the reasons described in our February report (Ehasz and Bowles2013). Each of these failure modes is described in detail in Appendix A of our February 2013report (Ehasz and Bowles 2013).P A 6 e-lO 4fI#f] m WWlIfmfaEJIEJ #EEJIWl L VALIDATION OF HRR BREACH H YDROGRAPH FOR JOCASSEE DAM4.0 CONFIRMATION OF JOCASSEE DAM ERODIBILITY4.1 OverviewDam erodibility is described by Xu and Zhang (2009) as a relative measure based on theembankment material compositions and compaction conditions, dam cross-sectional geometry,construction time and other relevant pieces of construction information. In their regressionanalysis, Xu and Zhang (2009) found dam erodibility to be the most important control Variablefor predicting all five breach parameters. The three erosion categories (Jow, medium or high)used in the Xu and Zhang (2009) equationS referenced the technical lecture paper by Briaud(2008), whereby soils and rocks are classified into various erosion resistance categories basedon water velocity or hydraulic shear stress at the soil-water interface (see Figures 4.1 a and 4b).Therefore it is significant to establish the compatibility of Xu and Zhang's application of theBdiaud erosion categories with the categorization, system developed by Briaud (2008).To directly address the erodibility questions and to develop a clear explanation of the threeerosion categories (low, medium and high) used by Xu and Zhang (2009) and the six erosioncategories (non-erosive, very low, low, medium, high and very high) developed by Briaud(2008), Professor Briaud made a site visit to the JoCassee Dam and participated in a face-to-face meeting with Dr. Yao Xu in Denver. A summary of the Professor Briaud's responses toseveral questions about the use of his erosion categorization Scheme by Xu and Zhang (2009)is provided in Section 4.2. A summary of Professor Briaud's independent evaluation of theerosion category for Jocassee Dam is contained in Section 4.3. Professor Briaud's completereport is contained in Appendix A.4.2 Use of Briaud's Erosion Categorization Scheme by Xu and Zhang (2009)The site meeting with Professor Briaud took place on October 3rd and 4th 2013 at the JocasseeDam site in South Carolina and at the offices of Duke Energy at the Oconee Nuclear Plant. Thepurpose of the site visit was for Professor Briaud to become familiar with the Jocassee Dam andthe materials used for construction. In addition, he was asked if his erosion categories areapplicable to erosion during an earth dam breach and specifically:* Is your (Briaud) work applicable to earth dam erosion?* What is your (Briaud) characterization of Jocassee Dam erosion characteristics?* Please comment on Xu and Zhang work on dam breach, and how 'the three erodibilityclassifications, used by Xu and Zhang, compare to your six classifications.P AG E..11 VAUO.ITJON OF: HRR BREATH HYDROGRAPH FOR JOCASSEE DAMDA%4urn+EROSIONRATE ISS,0.I,IlI.. 1O IUV1ELOCITY (rn/a)Figure 4.1a. Overall erosion category for Jocassee and Toton Damns (velocity based )iDfl tiII16 066 r 0 IIJ()f +%%tIFlIONEROSIONRATE IN -(mm/br)O.'II,KochVwL.uS I I.I Ili, 1i1111 Iew 101msSHEA.+R (Pu)Figure 4.lb. Overall erosion category for Jocanssee and Tetan Dams (shear stress based)Professor Briaud prepared a detailed report on his site visit to Jocassee Dam (Briaud 2013) andhis answers to the above questions (see Appendix A). A summary of his responses is asfollows:*Is your (Briaud) work applicable to earth dam erosion? The erosion function ischaracterizing the behavior of the soil at the element level so it is broadly applicable tomany erosion siutos, including the erosion and breach process for earth and rockfiliembankment dams. The erosion function is the curve which links the erosion rate to thewater velocity or the hydraulic shear stress at the sol-water interface; it is to erosionstudies what the stress strain curve is to deformation problems. It is a consiutvequation, which can be used in numerical methods as easily as in simple handcalculations.P AG e 12 VALIDATION OF HRR BREACH HYDROGRAPH FOR JOCASSEE DAM*What is your (Briaud) characterization of Jocassee Dam erosion characteristics? Theerodibility of the Jocassee Dam materials was. evaluated; and the Jocassee Cross-section materials are clearly and conservatively established to be "low erodibility"materials (see Section 4.3).*Please comment on Xu and Zhang work on dam breach, and how the three erodibilityclassifications, used, by Xu and Zhang, compare to your six classifications. The XU andZhang regression equations do show and consider that erodibility is the most significantfactor in the development of embankment breach parameters. Thus, it is mostimportant, in my evaluation of their" equations, that I have found that Xu and Zhang haveassigned tlhe "low, medium or high" erodibility categories in a way that is consistent withmy research findings for the variousdams represented by the data Used to establishtheir regression equations. The categorization reflects the fact that the types ofmaterials typically used for the construction of earth dams fall into the Briaud erosioncategories 2, 3, and 4 with some Category 5 materials for rockfill dams. Indeed finesands and non-plastic silts (Briaud category 1) .and jointed and intact rock (Briaudcategory 6) are not Used in earth da m engineering.4.3 Confirmation of Low Erosion Category for Jocassee DamTo evaluate the erosion category for the Jocassee Dam, the following process. was Used byProfessor Briaud:* A cross section of the dam was drawn, see Figure 4.2.* An erosion category was chosen for each material within thedam based on the specifiedvalues of the median particle size, Dho (see Table 4.1); since the drawings specified thatthe D80 was the minimum allowed, this selection is conservative.*Three erosion levels were placed across the dam as shown on the Figure 4.2 at levelsAA, BB, and CC,*For each level, a weighted average of the erosion category was determined according tothe length of material exposed to the flow for that level:c I=i L, EC,*. Where EC is .the average erosion category,. L1 is the length of material i exposed towater, and EC1 is the erOsion category for material i (low = 4, medium = 3and high = 2).* Section AA gave an EC value of 3.93, section BB gave 4.08, and =section CC gave 4.11.* Therefore, the overall average erosion category for Jocassee Dam is clearly .4 or lowerodibility.SP AG6E 13 l(~ l,~~ -VVIUIUtQIQ ai[Oiii p.uuIwt per :u i..rt't VALIDATION OF HRR BREACH HYDROGRAPH FOR JOcASSEE DAMFigure 4.2. Jocassee Dam cross section used in determination of erosion categoryTable 4.1. Jocassee Materials Evaluation by BriaudMaterial Estimated critical Erosion(Figure 4.2) Description velocity (mis) Category(b)(7)(F)Rock fillImperviouscoreRandom fillFiltersThe above conservative analysis by Professor Briaud clearly shows that the erosion category ofthe Jocassee Dam is low or Category IV, for erosion rates based on velocity or shear stress asshown on Figures 4.1a and 4b, respectively.A similar evaluation was conducted by Professor Briaud for the Teton Dam since this dam wasused by Xu and Zhang (2009) as an illustration and evaluation of their original regressionequations. In addition, an application of the revised Xu and Zhang regression equations to theTeton Dam failure is reported in Section 6.5. Professor Briaud showed that the erosioncategory of the Teton Dam is at the boundary between medium and high or Category Ill/il, forerosion rates based on velocity or shear stress as shown on Figures 4. Ia and 4b, respectively.The high resistance to erosion (low erodibility) of compacted rockfill has recently been affirmedby the experience of flooding and water passage through a rockflll embankment in the February2014 flooding at the Tokwe-Mukosi Dam in Zimbabwe. The Dam is a Concrete Faced RockfillDam (CFRD) and experienced an extreme flood during construction prior to placement of theconcrete face. It successfully passed extreme floodwaters through the compacted rockfillembankment with only local raveling and maintained stability. See Appendices C.1 and 0.2 fora description and photo s.P A GE 1.4

.,;,.,., -~;.';,;,,.;, ;,,.,, i.-;.;;., hlI.,; ,p,,. K SVALIDATION OF HRR BREACH HYDROGRAPH FOR JOCASSEE DAM5.0 ORIGINAL XU AND ZHANG REGRESSION EQUATIONSin our February 2013 report (Ehasz and Bowles 2013) it was concluded that the HRR (DUKe2013) breach hydrograph for the: Jocassee Dam iS a realistic but conservative breachhydrograph that has good defendability based on the following:1) the validity of the Xu and Zhang (2009) method;2) the conservative nature of the median brec aaeter estimates:3) a piping failure mode initiating in thel jjjj(I4), the deposition of rockfill immediately below~the dam;5). the low erosion category of the rockfill material; and6) the various characteristics of a modern dam that were included in the design and.construction of the Jocassee Dam.The original Xu and Zhang regression methodology and its previous implementation toJocassee Dam are described in Appendix B. This appendix provides background for Section 6.where we address the questions raised by the FERC .and the NRC. It also provides backgroundfor section 7 where we describe the implementation of a revised version of the Xu and Zhangequations in a sensitivity analysis, which provides support for the breach hydrograph submitted'in the Hydrologic Reevaluation Report (HRR) to the NRC .by Duke on March 12, 2013 (Duke2013).Section B.2 Summarizes the breach parameters and control Variables in the Xu and Zhang(2009) regression equations. section B.3 discusses the case histories that were used todevelop these equations and B.4 summarizes the regression equations, including theirconfidence limits. The implementation of the original Xu and Zhang (2009) methodology for theJocassee Dam is described in Section B.5 and details of the use of the failure time estimate inthe HEC-RAS model are discuss~l in Section B.6.P AG6E 15'

'VJI5 517 l~tw mlllVID1la *V. -IrWIrn4I55 *V*4l**.'.*d*ll¥ Hl~ W ,..r I [I LI.IIl.J U VALIDATION OF HRR BREACH HYDROGRAPH FOR JOCASSEE DAM6.0 REVIEW AND REVISION OF XU AND ZHANG REGRESSION EQUATIONS6.1 Approach to Review and RevisionThe FERC and NRC questions about the use of the Xu and Zhang (2009) methodology aresummarized in Section 2.2 and are repeated here:1) Precedence -where has use of the Xu and Zhang (2009) methodology been accepted?2) Chinese case histories -about 43% of the dlam failure case histories on which the Xuarnd Zhang (2009) methodology is based are for Chinese dams for which littleinformation is available in :the US.3) Representation of case histories for roclcflll and other low erodibility dams -thedata set of dams used by Xu and Zhang (2009)to develop the regression equations hasonly three dams that are considered large (i.e. > 15 meters high) embankment damswith low erodibility and both of these dlams are all outside of the US.4) Use of the Briaud erosion categories -how Were the erosion categories developed byBriaud (2008) applied in developing the Xu and Zhang (2009) methodology and are theyapplicable tO dam breach?5). Breach time definition,- the definition of time to failure used by Xu and Zhang (2009),includes at least part' of the breach initiation phase in addition to the breach formationprocess unlike other regression methods that include only the breach formation process.To respond to these questions raised by the regulatory agencies we arranged for the primaryauthor of the Xu and Zhang,(2009) technical paper to meet with us in the Denver Offices of URSduring the period, November 7 -10, 2013. Those in attendance were Dr. Yao Xu of the ChinaInstitute of Water Resources and Hydropower Research, Dr. David Bowles with RAC Engineers& Economists and, Utah ,State University, Professor Jean-Louis Briaud with Texas A&MUniversity, Joseph Ehasz with URS, and Adam Johnson from Duke Energy. On the morning ofFriday November 8, Dr. Xu and Professor Briaud independently met with Tony Wah!, BruceFeinberg and Dan Osmun of the Bureau of* Reclamation (Reclamation) at Reclamation'sHydraulics Laboratory in the Federal Center near Denver. This meeting was in response toTony Wahr's request to meet with Dr. Xu-during his Visit to the US to discuss his questionsregarding the Xu and Zhang (2009) methodology.The four-day working session was divided into two parts: first discussions of the agencyquestions and. second a detailed case-by-case ,review of the 75 case histories that were used todevelop the original Xu and Zhang (2009) regression equations. The ultimate objective was tomake appropriate changes to the Xu and Zhang (2009) case histories data set to address theagency questions and any other issues identified during our review so that Dr. Xu could developrevised regression equations.P A GE 16

~VALIDATION OF HRR BREACH HYDROGRAPH FOR JOCASSEE DAMA summary of our discussions with Dr. Xu and Professor Briaud for each of the questions raisedby the FERC and NRC and for some additional issues that were identified during thesediscussions is presented in Section 6.2. 'Specifically, these additional issues, which arediscussed in Section 6.2.6 -6.2.8, were'as'follows:1) Erosion category assigned to dams with corewalls anid concrete-faced rockflll dams2) Differences in values of breach parameters and control variable in other sources,especially Froehlich (!995a and'b and 2008) and WahI (1998)3) Inconsistencies between peak br~each flows~and breach development timesThe changes made to the data set of case histories are summarized in Section 6.3 and detailedin Appendix D. The revised regression equations are presented in section 6.4 and their testimplementation for Teton Dam is discussed in Section 6.5. Their implementation for JocasseeDam as a sensitivity study to evaluate the HR R hydrograph is presented in Section 7.6.2, Summary of Review Findings6.2.1 PrecedenceIn the U.S. dam safety community the acceptance of new methodologies often comes throughadoption by the rniajor government dam, owners ,and regulatory ,agencies. These agenciesinclude the US Army Corps of Engineers (USACE) and the Bureau of Reclamation as majorgovernment datm owners and the FERC as the federal regulator for hydropower dams. As withany new methodology it takes time for it to become accepted into practice and for precedence tobe established. From'this perspective the Xu and Zhang (2009) methodology is st~i quite new.In, the case of the Xu and Zhang (2009) methodology, the questions raised by the FERC and theNRC must be addressed as part of the process if this methodology is to become more widelyaccepted. Addressing these questions is the purpose of this section of the report.The inclusion Of erodibirity in the Xu and Zhang (2009) regression methodology is widelyrecognized *as a Significant advantage over other breach parameter estimation regressionanalysis methodologies. In fact Xu and Zhang (2009) demonstrated that erodibility is the singlemost important control variable in Ipredicting all five breach parameters. Such a significantadvantage justifies a careful evaluation of the Xu and Zhang (2009) methodologyto0 see if it canbe more rapidly put to use in the profession.H i i .wp i i l .... ..........El * *~~* l 5lll'*t~tZltl*

5.. .a E U .* t n ., *.a-. *- -'VALIDATION OF HRR BREACH HYDROGRAPH FOR JOCASSUE DAMThree uses of the Xu and Zhang (2009) methodology have been identified, as follows:1) In developing a Simplified risk assessment procedure for small reservoirs for theequivalent of the dam safety regulator2 in England and Wales [the Environment Agencyand the Department for Environment, Food and Rural Affairs (Defra)], HR Wallingford(2014) evaluated the Xu and Zhang (2009) methodology for estimating peak breachflows. In' their comparative study they concluded'that the Froehlich (1995a) and Xu andZhang (2009) approaches both 'yield "conservative, estimates of peak breach flow forhighly erodible embankment dams and that the physically-based HR BREACH model(Mohamed 2002) and the simplified AREBA model (HR Wallingford 2012) provide morerealistic estimates.2) The Xu and Zhang (2009) methodology included in the breach parametermethodologies that are available in the USACE HEC-RAS computer model, which Iswidely used in the US for dam breach modeling. It Was also included in a discussion of"Hydraulic modeling aspects that are unique to performing a .dam break analysis" byBrunner (2011), who is the USACE Hydrologic Engineering Center (HEC) technical leadfor the HEC-RAS model. In both cases a caution is given that "the data Xu and Zhangused in the development of the equation for breach development time includes more ofthe initial erosion Pieriod and post erosion period than what is generally used in HEC-RAS for the 'critical breach development time" (Brunner 2011). In addition it is statedthat-".. because of this fact, the XU and Zhang equation .for brea'ch development timeshould not be used in HEC-RAS" (Brunner 2011). However, in a PersOnalCommunication (December 2013) with Dr. Brunner he agreed that it was. reasonable to*iteratively change the breach progression relationship and the values orifice and weircoefficients in the manner described in Section B.6 for Jocassee Dam when using failuretime estimates based on Xu and Zhang '(2009). He also expressed interest in replacingthe original Xu and Zhang (2009) regression relationships in HEC-RAS with the revisedrelationShips that are described S ection 6.14.3) We understand from Dr. Xu that the Xu and Zhang (2009) methodology is being appliedby government agencies in China.6.2.2 Chinese Case Histories.About 43% or' 32 of the 75 dam failure case histories on Which the Xu and Zhang (2009)methodology is based are for Chinese dams. None of these case histories are included in theWahl (1998) data base of case histories, although :that data base' may be due. for anupdlate andif one is undertaken it would seem beneficial to include Case histories from China.2, In England and Walesthe Environment Agency ,is responsible. for enforcement of reservoir safety requirements forspecific reservoirs "in the: interest of safety" that 'are determined by Panel Engineers who .are appointed by theSecretary for State. Defra has a policy role for deveiopmnent of reservoir safety legislation and guidance.P A 6E 18 In'urmr~nin- wannwu ,rrum puDIIc asciosuiweper "U (~i.C [LJWu(O)~~JRS In association withRCVALIDATION OF HRR BREACH HYDROGRAPH FOR JOCASSEE DAM-SIn discussing the quality of data for the Chinese case histories, Dr. Xu stated that he felt that theavailable information was similar, in quality to what he had examined in his research for: casehistories from. the US' and. some other countries. In at least .two cases-detailed failureinvestigations reports have been prepared for the Banqiao and. Shimantan failures. Dr. Xureferenced a report by Ru and Niu (2001), which contains information on many Chinese dambreaches. This report, is readily available outside of China. He also had access to a detaileddatabase on dam failure Case histories, but this is not available outside China. However, Dr. Xumade extensive reference to this data base during-our detailed evaluation of the case, historiesthat were used as a basis for developing the Xu and Zhang (20.09) regression methodology (seeSection 6.3)..Dr. Xu also described a screening process that he performed before using the case history datafrom China and other countries in his regression analysis. Any case histories .where .significantConcerns existed about the quality of the available data were omitted. It should be noted thatthe Chinese data used by Xu include some more recent-dam breaches than used by others,such as Froehlich (1995 and We also enquired about the quality of construction, for the Chinese .case history, dams. Dr. XUindicated that dams designed and constructed before 1977 were not up to modern standards,and that modern construction methods and ,equipment were not used. Dams. constructed 1977 can be considered to meet modern standards. The .significance for Chinese caseis first that there are more of them because of the poorer standards prior to 1977.Secondly, the poorer construction, and in particular the poorer compaction .of Chinese.embankment dams constructed prior to 1977, would be expected to result in a more erodible-dam once a breach process has initiated. Unlike most other regression methods, for estimatingbreach parameters, thel XU and Zhang (2009) approach includes the erosion category as ameans of accounting for the more erodible characteristic of the Chinese dams that wereconstructed prior to 1977. The .approach adopted' by Xu and Zhang (2009) to account for theeffect of poor construction in the development-of their regression equations is summarized inSection .6.2.4. We also make reference to this .approach in. Section 6.3.2, in which wesummarize the critical review that we. performed of the entire Xu and Zhang (2009) data set,including all Chinese case histories.In summary, Dr. Xu demonstrated the overall validity of his' evaluation, of the case history, datafrom all sources, including and that good. backup information exists, although, for someChinese case histories access to this information is restricted. For the Chinese Case historiesthis conclusion is based on the detailed information that Dr. Xu provided from the data. sources.of failure analyses and records, which he accessed during the detailed .review that we.conducted with him over" a four-day period. Our detailed evaluation of all case histories issummarized in Section 6.3 and notes for specific case histories are presented in Appendix D. Inaddition, based on our detailed review (see section 6.3), we found that in a majority of-thecases a valid assessment of the case histories was performed by Xu and Zhang .(2009) as theP A 6, 19r

,,uuo u,=o ,.u ,... n .= ...vvvw= I--- -- -- --VAIJDATION OF HRR BREACH1 HYDROGRAPH'FOR JOCASSEE DAMbasis for the values assigned to the control variables-and breach parameters that were used inthe regression analysis. The exceptions,, which resulted in our making some adjustments to theassigned values, are discussed in Section.6.3 and documented in Appendix D. The revisedvalues were used in the revised regression analysis that is presented in Section 6.4 and used ina sensitivity analysis on the HRR breach hydrograph that is presented in Section 7.6.2.3 Representation of Case Histories for Rockfill and Low Erodibility DamsThe small number of case histories' for rockfill dams that are classified in the low erosioncategory is a reality :that is likely due to the intrinsic safety' of rckfill dams in general. Anotherlimitation is the lack of case histories of the failure for large .(high) dams with a reservoir capacitysimilar to Lake Jocassee. This can be clearly seen in Figures B~la and b. However, whenvolume is plotted logarithmically in Figure which corresponds to its representation in the.multiplicative regression equations, the extrapolation from the range of case histories to LakeJocassee for The reservoir volume above the breach invert can be seen to be relatively lesssignificant.These limitations apply to all breach parameter regression methodologies. However, Xu andZhang (2009) offset, these limitations to some extent by including case histories from China forthe Danghe and Gouhou large rockfill dams. In addition, their inclusion of the Briaud (2008)erosion categor'ies as a control variable was another innovation that was intended to account forthe important effects that differences in the erodibil ity of materials in embankment dams have onbreach parameters. Still regression equations are limited in. their ability to explain all thevariability' that exists in the available case history data. ,In contrast physically-based approachesare less limited than regression equations because they introduCe a ,representation of thephysics of the erosion, instability and hydraulics phenomena that determine breach processes,.However, these approaches must be used in an appropriate manner that accounts for their ownlimitations and the resulting uncertainties in predictions when used to develop breachhydrographs.6.2.4 Use of the Briaud Erosion CategoriesWe asked Dr. Xu what information he used as the basis for the assignment~.of erosioncategories to the case histories used in developing his regression equations. He described two-step process. In his first step the soil type within the dam was used to assign a range of erosioncategories as low erodibility (LE) to medium erodibility (ME) for rockfill and clay and ME to higherodibility (HE) for silt and sand.: The second step was to evaluate the construction quality,particularly compaction effort, based mostly' on the period of construction to determine whichend of the range of erosion categories to assign. For example, the period 1950 to 1976 inChina, would be Characterized by .low compaction using human powered tampers, and afterabout 1977 in China high compaction would be achieved using machine rollers. Other usefulP AG E 20

..... ................. .. ................................W ' .I fII S I socainwtVALIDATION OF HRR BREACH HYDROGRAPH FOR JOCASSEE DAMpieces of information such as dam cross-sectional :geometry, materials and slope surfaceprotection were used as supplementary information for assigning the dam erOsion categories.Professor Briaud's independent review confirmed the appropriateness of using *his erosioncategories for dam breach parameter estimnation in the Xu and Zhang (2009) methodology. Hisreview is summarized in Section 4 and detailed in *Appendix A.The two-step approach dlescribed above is consistent with the Briaud (2008) erosioncategorization approach as summarized below. The dam erosion categories high, medium orlow are described by Xu and Zhang (2009) as a relative measure based on !the embankmentmaterial' compositions and compaction conditions, dam cross-sectional geometry, constructiontime and other relevant pieces of construction information. Briaud (2008) found that the rate oferosion can be very different for different soils that are classified in different erosion resistancecategories. Specifically, rockfill and clay are often associated 'with. medium to low erosioncategory while sand and silt are often associated with high to medium erosion category. Hence,material compositions are considered as, a primary basis for classifying dam 'erosioncategory. In addition, compaction conditions also play an important role in determining the damerosion category, especially for dams constructed from fine soils. Briaud (2008) reported thatthe erosion resistance increases With compaction effort and that the effect is more significant forsome soils with high fines contents. It was also indicated by Wan and Fell (2004) that thererosion rate index of a soil is inflUenced strongly by the degree of compaction. As described byDr. Xu, thle year Of construction and the associated compaction methods were thereforeimportant information for judging the compaction condition of the case history damns, and hencethe* assignment of dam erosion-categories.6.2.5 Breach Time DefinitionAs is well recognized, the predicted breach from Xu and Zhang (2009) are significantlylonger than those obtained* from other methodologies such as Froehlich '(1 995b and 2008). Xuand Zhang (2009) based their definition of breach development time on the definition by Wahl(2004), which states that development begins when a breach has reached the point atwhich the volume of the reservoir is compromised and failure becomes imminent" and bendsWhen the breach reaches its final size."; By 2013 WahI (2013) revised his breach time definitionto be consistent with Froehtich (1995b 'and 2008). The difference between the definitions offailure time used in the original Xu and Zhang (2009) methodology based on Wahl (2004) andby-others is discussed in detail in S ection B.6.We found that of the 30 case histories that were :used by Xu and Zhang (2009) to establish theirregression equations for breach development time, only five also appear in the Froehlich (2008)data set. 'Of these five, three have the same values for breach development times in both datasets but for two (Apishapa and Teton dams) the Xu and Zhang (2009) values are just over threetimes the Froehlich (2008) valueS. In our detailed review of the case history data (see SectionP A 6 E 22.

.L: .... ..... ..........,.r .-lUI mffpigIp(iUI aIgaIIa U -F-"-.-.- --VALIDATION OF HRR BREACH HYDROGRAPH FOR JOcASSEE DAM6.3) we addressed this inconsistency by changing these values of breach development timestomatch the Froehlich (19 95b and 2008) definition based on avail able information.In our detailed review we found that in a few cases lower erosion categories had been assignedto damn breaches that had long observed failure times when all other available information aboutthe damn, the materials from it was constructed, and the quality of construction pointed toa higher erosion category. In our detailed review of the case history data we changed these toa higher erosion category for developing the revised regression equations that are sensiti vitystudies presented in Section 7, since in applyin~g the regressioni equations one'would haVe nobasis for this type of adjustment of the erosion category.6.2.6 ErOsion Category Assigned to Dams with Corewalls and Concrete Faced Rockfill DamsIn our detailed review of the case history data, we found that the term "corewall'" had been usedfor some dlams that had a claY core but not core wall constructed of concrete, masonryor steelto distinguish them from homogenous fill dams with no clay core. This was apparently amisunderstanding about the use of terminology in English and we corrected this in assigning thedam type control variable in the data set that was Used for developing the revised Xu and Zhangequations.In some case we found dams thatl were assigned a. low erosion category as an indirect meansof accounting for the throttling effects on breac~h development in embankment dams with aconcrete core wall or for concrete-faced rockfill dams (CFRD). While this approach has somemerit, it was judged that the breach parameters for embankment dams with a concrete corewallor CFRDs would not be representative of 'the erosional process' in low erodibility embankmentdams in general,, and so we excluded dams with' a core wall or a concrete face from-the data setthat was used to develop the revised Xu and Zhang reg ression equation s (see Section 6.4).6.2.7 Differences in Values' of Breach Parameters and Control Variable in Other Sources,All values of the control variables and br'each parameters in the Xu and Zhang (2009) data setwere compared with those found in other sources,, including the following:* WahI (1998) "best reliable information"*- Froehlich (1 995a and b and 2008), 'VonThun and Gillette (1990)* Costa (1985)*- Waider and O'Conner (1997)* MacDonald and Langridge-Monopolis (1984)P A, Ge 22 VALIDATiON OF HRR'BREACi' HYDRoGRAPH FOR JOCA SSEE DAMPreference Was generally given to adopting values contained in the first two sources, althoughwhere available additional sources were consulted ,to verifY or change Xu and Zhang (2009)data set values. These additional sources included Singh (1996) and various internet sourcesthat are referenced in Appendix D. The changed values were used to develop the revised Xuand Zhang regression equations that were used for the Sensitivity studies that are Presented inSection 7.6.2.8 Inconsistencies between Peak Breach Flows and Breach Development TimesAn inconsistency was identified in many case histories between the peak, breach flowS, breachdevelopment times and the reservoir volume above the, breach bottom at the time of failure.The inconsistency exists for many case histories in the Wahi (1998) data base and in theFroehlich (1995a and b and 2008) data as well as in the Xu and Zhang (2009) data. Theinconsistency was identified by assuming that the breach outflow hydrograph has a generaltriangular shape with the base of the triangle representing the breach development time, theheight the peak outflow rate, and the area of the triangle the volume of reservoir Contents abovethe breach bottom elevation. Under this assumption an approximate breach formation time canbe calculated from simple geometry as follows:T = 2Vw/Qp (6)in which:T = Breach development timeVw Volume Of reservoir contents above breach invert atthe time of failureQp= Peak breach flOW rateOn the basis that. the observed Values of Vw and Qp can generally be obtained with greateraccuracy than the observed value of T, we compared the values of T calculated using .Equation6 with the observed values in the .case histories: used by Xu and Zhang (2009) and those inWahl (1998)r and Froehlich (1995a and b and 2008) and found significant differences, To avoidchanging the case history values Of T in the widely accepted Wahl (1998) and Froehlich (1995aand b and 2008) data sets, we used those values to develop the revised Xu and Zhangregression equations that were used in the sensitivity, studies. However, we found, notunexpectedly, that this inconsistency resurfaces, when a similar comparison, is madea betweenpredicted values of the breach development time and those obtained from Equation 6. Wediscuss this issue further in Section 7.2 and the approach that we have developed to address it.P A 6 E .23 C.z---.; ....., ..... [;;,--.= v' -;, .,,, puum. , I;.ir;burw per w' t..iN £.J~u(UJVALIDATION OF HRR BREACHI HYDROGRAPH FOR JOCASSEE DAMi ill.i p6.3 Summary of Revisions to Case History Data Set6.3.1 ApproachDuring the Denver meetings the group questioned Dr. Xu about each of the 75 case historiesthat were used to develop the original Xu and Zhang (2009) regression equations. All values ofthe control variables and the breach parameters for the case histories were discussed andreviewed and notes were recorded in a spreadsheet (see Appendix D) during the meeting andto record the results of further scrutiny following the meeting. Professor Briaud assisted in thedetailed erosion category review and this resulted in changes to several case histories.In addition, all values of the control variables and breach parameters in the Xu and Zhang(2009) data set were compared with those in other sources that are listed in Section 6.2.7 andadjusted as appropriate.6.3.2 Summary of Xu and Zhang (2009) Data Set Revisions used in the Sensitivity StudiesA summary of the types of changes that were made were to the Xu and Zhang (2009) data setis as follows:* Changed breach development times to the Froehlich (1995b and 2008) definition ofbreach developm ent time.* Changed the values of other variables where they were inconsistent with the Wahl(1998) and Froehlich (1995a and b and 2008) data with consideration given to otherreliable information that was found in various other sources m entioned in Section 6.2.*Changed assigned erosion categories to include the consideration that compactionassociated with construction practices in the US and other developed countries (notChina) improved for earthfill dams after about 1950 and for rockfill dams after about1965. This is similar to the consideration used by Xu and Zhang (2009) for Chinesecase histories before and after 1977.* Changed to higher erosion categories cases where lower erosion categories had beenassigned because of long observed failure times but where all other availableinformation about the dam, the materials from which it was constructed, and the qualityof construction pointed to a higher erosion category.* Eliminated case histories for concrete-faced dams and dams with core walls or cut-offs(discussed below).The above changes were made to improve the quality of the data used in the revised regressionequations and to achieve consistency with the commonly-used Froehlich (1995b and 2008)definition of breach development time. In principle this definition was seen as a way to assignthe duration of the breach hydrograph that is commonly developed using the HEC-RASsoftware; but as demonstrated in Section 7.2, it was found that another step was necessary toP A GE 24 L...... :. ~ ~ -u,,~mn,,rjprx ,rflm nairuiu~ ,i,~i~in~iir~ ~51r Ill i:i-i# Ti .AqflIflI* .. ... Hv *

v v. * * *

vK E S In association with C~EIIVALIDATION OF HRR BREACH HYDROGRAPH FOR JOCA$$EE DAMestimate a breach development time that is consistent with the predicted values of peak breachflow and the reservoir volume above the breach bottom at the time of the breach. Overall thenumbers of changes to US, China and other country case histories in the .original Xu and Zhang(2009) data set were as follows:* Reservoir capacity: 3 US changes* Dam erosion categories: 10 changes comprising 4 US, 5 China and 1 Brazil* Failure modes: 3 US changes* Volume of water above breach invert: 5 US changes* Depth of water above breach invert: 2 US changes* Breach height: 2-US changes* Breach average width: 4 US changes* Breach side slope: 2 U S changes* Breach failure time: 9 changes comprising 6 US, 2 China and I BrazilIn addition to these changes, twenty out of the 75 case histories used by Xu and Zhang (2009)were eliminated for the following reasons:* Concrete-faced dams: 5 total, I Argentina (Frias), I China (Gouhou), 3 USA (DavisReservoir, Horse Creek, Swift)* Dams with core walls or cut offs: 8 total, I China (Danghe), 1 UK (Coedty), 6 USA(Castlewood, Elk City, Lower Otay, Lynde Brook, Winston, Wilkinson Lake)* Lack of reliable information: 6 total, 2 China (Niujiaoyu, Huqitang), 4 USA (Potato HillLake, Trial Lake, Upper Pond, Otter Lak e)* Not representative due a large volume reservoir with a small height dam that resulted ina long breach development time and a very wide breach: I US A (Hatfield)The concrete-faced dams and dams with core walls were removed because their breachcharacteristics would not be representative of the erosional process for breaching ofembankment dams in general. Specifically the concrete membrane would be expected to resistbreach development and to have a throttling effect on breach development. Xu and Zhang(2009) assigned a low erosion category as an indirect means of accounting for these effects of acore wall or concrete face but this was judged to. bias the data set.Given more time it is possible that additional information may have been obtained for somecases that were eliminated due to a lack of reliable information. Also it is possible that someaccepted US and other developed country case histories, which were not included by Xu andZhang (2009), could have been added to the dat a set.P AGE 25 VALIDATION OF HRR BREACH HYDROGRAPH FOR JOCA4$$EE DAMLastly, and despite the Scrutiny imposed on the data ,from China :during our meetings, theChinese case histories were omitted from the data set that was used: to develop the revised Xuand Zhang equations used in the Sensitivity studies. This step was taken toincrease confidence in the revised Xu and Zhang regression equations by avoiding the potentialcriticism that we had only limited and indireCt access to the original references for the Chinesecase histories. However, this step further reduced the total number of case histories from 55 to27.The numbers of case histories that Were used to estimate the revised best exact and best*simplified *equations, respectively, are as listed below:.Breach depth (H b): 23 and 23* Breach top width (Bt): 21 and 24.Average breach width (Bare): 22 and 24* Peak outflow rate (Qp): 16 and 19* Breach development~time or failure time (TO): 14 and 14These are significantly fewer than for the original Xu and Zhang (2009). However, as can beseen from Figures 6.1a and b, they cover the same range as the original data set. Figures 6.1aand b are similar to Figures B~la and b. Figures 6.la and b show the :depth of water abovebreach invert, Hw, and volume of'water at the breach time, Vw,, on arithmetic-arithmetic andadithmetic-log axes, respectively, for the 75 case hitds teoriginal Xu and Zhang (2009)data set and the 55 case histories in the revised data set. The 27 US or other country dataremaining after the Chinese data are om itted can also be identified in these figures.The revised data set include three low erosion category case histories, 11 medium erosioncategories and 13 high erosion categories. It includes seven overtopping failures and 20seepage-erosion failures.6.4 ReVised Regression Equations for use in the Sensitivity StudyDr. Xu personally developed revised regression equations for the best exact prediction using allfive control variables. He also developed the best simplified prediction equations as those thatgave the highest R2dj as obtained through a stepw ise regression procedure (see Section B.4).The revised Xu and Zhang regression equations were developed using the revised case histonydata as described in Section 6.3. As eXplained in Section 6.3.2, the. Chinese case histories.were excluded from the revised regression equations that we used in the sensitivity study toevaluate the approprilateness of the HRR breach hydrograph.P A 6 E 26,i VA UDA In~ OF HRR BREAO. HVMGRP FOA JOC4SSEE DAMOdIginal and Revised Ku and Zhang DataI807OI.I.°:0iI0IU*USA. OrWmnA Other IUjcuse. -OrignalX Clnr -RevisedOther -RleviseXlocassee -Reid00 400 60 800 1000*bu. .m WII, ab:e, nv~irt Vae (a 105mrol1200 14100a) scalesOriglinal and Reie Ku and ThanI DataItNNII7018I°401401w°rO100~.Nx x,, *mI Clna -Or~lnalOter.- Orignal-OrtIgnalM ua.n RevisedKiCasmee -Re~visedx0.1 1 10 100*4. of ,,wemim hImwt Vw (a 1OS m3)b) ArIthmetic-logartthmic scalesFigure 6.1. Depth of water above breach Invert vs. volume of water at the breach time forthe original and revised Xu and Zhang case histories.P AG0E 27 JRhS InaoctonWtlLCVALIDATION OF HRR BREACH HYDROGRAPH FOR JOCASSEE DAMThe coefficients for the revised regression equations are presented in Tables 6.1 and 6.2 for thebest exact and best s implified prediction equations, respectively.6.5 Application to Teton Darn FailureThe revised Xu and Zhang equations were applied to the Teton Dam using the same controlvariable values as shown in Table 10 of the Xu and Zhang (2009) paper. We selected TetonDam for this evaluation since, like the hypothetical failure for Jocassee Dam, the Teton Damfailed by piping, whereas the other dam evaluated by Xu and Zhang (2009), Banqiao Dam, wasan overtopping failure. Since the evaluation of the erosion category by Professor Briaud, whichis summarized in Section 4.2 (see Figures 4.1a and b), indicated that the Teton Dam lies on theboundary between the high and medium erodibility categories, we applied the revised equationsfor the high and medium erosion categories and then averaged the two Sets of median predictedvalues.Tables 6.3 and 6.4 contain the observed and predicted values of the breach parameters for theoriginal Xu and Zhang (2009) and the revised Xu and Zhang described in Section 6.4 for thebest exact and best simplified equations, respectively. Two values of observed breach time areshown, 4 hours4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months for the original Xu and Zhang (2009) definition of breach formation time and1.25 hours2.893519e-4 days 0.00694 hours 4.133598e-5 weeks 9.5125e-6 months for the definition of breach formation time that is used in the revised Xu and Zhangequations based on the Froehlich (1 995b and 2008) definition. In addition to displaying themedian predicted values, the percent differences between the observed and predicted medianvalues are presented. The lowest percent differences for the original Xu and Zhang (2009) or*the revised Xu and Zhang equations are indicated in red. For the best exact equations (Table6.3) the revised approach yields smaller percent differences than the original equations for threeout of five breach parameters. For the best simplified equations (Table 6.4) the revisedapproach yields smaller percent differences than the original equations for four out of fivebreach parameters. Therefore, for Teton Dam, the revised equation predictions have smallerpercent differences with the observed values than the original X u and Zhang (2009) predictions.The revised regression equations were also evaluated for the Teton Dam based on a meanbreach time estimate that was obtained from the uncertainty distribution on predicted peakoutflow and the volume of water released through the breach. The basis for this estimate isdiscussed in Section 7.2 in which the mean estimate is distinguished from the median estimate,which results directly from the multiplicative regression equations for all breach parametersexcept breach depth. The resulting estimates are provided at the bottom of Tables 6.3 and 6.4for the best exact and best simplified equations, respectively. In both cases they significantlyoverestimate the observed breach time. However, these estimates may be reasonable for areservoir with the stored volume that Teton had at the time of its failure and that the observedbreach time was shorter than predicted by the regression equations because of an unusualfailure mechanism that has been documented by the Teton Dam owner, .the Bureau ofP AG E 28

... ... aJ at_ -" ...........IIIIU#IalOUUeII -- -- ...........1IF --JVAUDA1TION OF HRR H VROGReAPH FOR JOCASEE DAMATable 6.1. Summary of the five revised Xu'and Zhang best exact regression equations __Breach Parameter Number Contr-ol bO J I j JS2yvlx(or-Variables .0lgO bi b2 b31 b32 633 b41 b42 b51* b52 b53 R12Y(orlogY) of Cases (lg on lonebr ) I ,,I s2ivyi1,)..:... .. ....... ..... ...... ..Reservoir _ _ __ Dam Type .mErodi1 lty_______ _.;.....Inecp it SaeCore Wall CFRD oogOvertop Piping High Medium °LowHb/A'4, 23 X1,2,3A4.5 0.449 -0.023 0.002 .0.134 ____ 0.138 0.1_78 0.271 0.222: 0.1.86 0.04'1 0.375 0.016Iog(Bt/flb) 21 lnX1,2;3,4,5 0.088 0.127 0.620. 0.122 ___ -0.053 0;.2,40 -0.328 0.246 -0.201 -0.133 0.594 .0O.213_________ 2 -______02 Coef. -0.425 ______ Zoned : f069 022 07 -0_1__ ___67_ 0.___7Iog[ave/HbJS/3 22 InX1,2,3,4.5 -0.308 ;0.029 -0.890 -0.452 -___ 0.409 -0..7.3 -0.759 -0.225 -0.378 -0.823 0.670 0.273Iog('17/ Tr) 14 INX12,23,4,5 -0.883 O.017 0.715 0.47 ___ -0.678 -0.232 .-0.619 -0.442 0.178 0.646 0.902Table 6.2._Summary of the five revised Xu and Zhang best simplified regression equations ___Breach Parameter Number- Contr-ol bO b b2 b 1 b 2 1 b 3 4 I 42 51 b 2 1 b S2vl5 (orY(orlogvl of Cases (tgnhier CorlogbO) .____ R S2tcezieX).Reserv'oirl__" _ Dam Type ____ ___ Erodibility Cate io/ ......Intercept Hgt Shape CoeWl ID HomogOero Ping ih Mdim .w_______Coef, __ore_ Wall ___R Zoned .Overtop Pii___ig __di_ LoHb/H~d 23 X1,45 0.673 -0.021 -______ __ .0,.,00. 0.089 0.297 0.26 0.117 __ 0.133 0.013Iog(Bt/Hb) 24 .InX2A4,5' -0.241 '0.72 ___ __ 0.121 40.363. 0.23 -0.027J 0.201 0.592 0.181Iog(Bove/Hb) 24. Inxz4,5 1.577. ___ , 0871 ,,,_ -1.122 -0;667 -1,346 -10O77 0.628 0.245lo p(Qo/i'gVw5/3) 19 InX2,5 -2.80 _O _ -1.222 ____-0.55 -1.069 -1.281. 0.84 .0.216Iag(TJ/Tr) 14 INX2,3,5 -1.382 ____ 0.859 .0.14 ____ -0.132 --0861 -05$3 0.009 0.085 0.538S ~PA 6 E -29 VAUDATION OF HRR BREACH HYRGRP FOR JOCA SSEE DAMTable 6.3. T,ObservedBreach Parameter UnitsValueHeight o breac m ___Breach top width m ___Avemeie breach width m 151Peak outfow Breach formation time -Original Au and Zhang hours ___Breach formation time -Revised Au and Thanl hours 1.E* ton Dam predicton using best exact equations[Oriinal Xuand H Revised Au and Thn PredictionsOriginal -MedianPercentDIffemrencValue wtObserved19 -7"hi *'752, 16 51,High Erodibillty Medium Erodibility Mdu rdbltDiffer-,nceUer Lower Median Upper Lower Medliant Value8 1 _4 51 1 _5 5 1 5 _4 15 %0. 0.7 9.i 1 0. (LI 1019 ZiZ I dtons using best simplified equationsRevised Xu and Thang PredictonsAverag High &HhErodibility Medium Er'odibtlity MdiI I J JPercentUpper1 Lower Median Upper Lower Median Value~ 2 jwit______ .J!L~ .521 ___O__ served_Table 6.4. TetcObservedBreadh Parameter UnitsValueielst oE breach m ____Breadh top width m 3Average breads withl m 151Breach formnation time -Original Au and hours 4__Brmadi fornstion time Revised Xu and hours mn Dam predicOrgirsal Au and m~anglj 2tl) redcitonsOriginal -MedianPercentDifferenceValue wt____ -11%12w -1651I 1161 (Lii 3.41 OMI (Lii &TW ~1MewP7s3PAGE 30 i.unwarw .wcura~y irormauon -wennow rrom puww* desciOwurw per wu w-K £.JWJ,(a)VALIDATION OF HRR BREACH HYDROGR4PH FOR JOCASSEE DAMReclamation (Osmun 2013). The failure mechanism involved the development of a large cavitypiping of the core materials into the downstream rock had been unnoticed. The piping hadwithin the dam. which formed due to the pervious nature of the foundation and the fact thatmoved embankment materials and continued for many days or even weeks and formed a largeCavity within the core/center of the dam. Once the cavity collapsed it caused a very suddenfailure with a shortened breach time, because a significant amount of material had already beeneroded from within the dam, causing an enlarged and sudden opening, which is uncharacteristicof a normal erosional breaching failure. This failure mechanism is discussed in more detail inAppendix C.2.P AG6E 31 VALIDATION OF HRR BREACH HYDROGRAPH FOR JOCA SSEE DAM7.0 REVISED XU AND ZHANG REGRESSION EQUATIONS SENSITIVITYSTUDIES7.1 Overview of ApproachA sensitivity study Was performed to explore the effect of the revisions made to the original Xuand Zhang (2009) regression equations on .the breach hydrograph for a piping failure ofJocassee Dam and compare with the HRR breach hydrograph submitted to the NRC by Duke(2013). The revised Xu and Zhang regression equations were applied to the Jocassee Dam toobtain the median estimates of the breach parameters and their confidence intervals. Therevised equations were for the case in which we used the Froehllch (1995b and 2008) breachtimes and with all Chinese case histories omitted.The spreadsheet that we used in our previous work to implement the original Xu and Zhang(2009) regression equations (Ehasz and Bowles 2013) was generalized such that a new set ofregression coefficients for the revised equations can be input. To calculate the confidenceintervals we also input the standard error of regression, the number of control variables, and thenumber of case histories used to develop each regression equation. The modified spreadsheetwas verified against the original version in which the regression coefficients were hard wiredand for the applications to the Teton and Banqiao Dams to verify that we closely matched theresults published by Xu and Zhang (2009).The breach parameter estimates obtained from the revised Xu and Zhang regression equationsare presented in Section 7.2. Section 7:3 contains an example of inconsistencies between peakbreach flow and breach development time for the Jocassee Dam breach hydrograph for thebreach Case 2(I00VV) submitted to the NRC by Duke in support of the Safety Evaluation (SE)(NRC 2011). The HEC-RAS implementation by HDR of the revised Xu and Zhang regressionequations breach parameter estimates to obtain a breach hydrograph for Jocassee Darn and acomparison with the HRR breach hy drograph are discussed in Section 7.4.7.2 Revised Xu and Zhang Breach Parameter Estimates for Jocassee Dam'The resulting median and 95% confidence interval estimates (lower and upper bounds) arepresented on the left Side of Table 7.1 for the revised best exact equations. In addition thebreach bottom elevation and average side slopes are calculated and displayed.For comparison, Table 7.1 .also displays the Froehlich (1995a and 2008) estimates of thebreach parameters. Considering the widths of the confidence intervals for both methods, thetwo methods provide fairly similar median estimates (see Figure 7.1). In particular the medianpeak outflows; median breach top widths and median breach formation times are quite Similar.The similarity of the median breach formation time estimates follows from changing thedefinition of failure time in the revised Xu and Zhang methodology to match that in FroehlichP AG6E 32

....... ... ... ... L.lr_'.-. ..".... : A..... J .. .......... ........ ..IJIUS In association with RALCVALIDATION OF HR R BREACH HYOROGRAPit .FOR JOCA$S£E DAMA...... it-......... l IVALIDATION OF HRR BREACH HVDROGRAPIY FOR JOCA SSEE DAMpTable 7.1. Breach parameter estimates from a) revised XU and Zhang without Chinesecase histories the Froehlich breach time definition, and b) Froehlich (1995a and 2008)Revised Xu and Zh ang Without (hina Frelc "9bn 08BreachParameter Froehllch Breach Times____________________ Upper Lower. Median i Upper Lower MedianHeigh1t of breach (feet) 7 7 2 25.7BreaCh formation time (hours) ,, Breach top width (feet) 2,78"7 363 1,009 3,384 ,587 1,082Average breach width (feet) 2,007 206 643 3,392' 395 889Peak outflow (cfs) 'b!)FBreach bottom elevation (feet msl) 743 9531 848 850/ 880 850Average side slopes (lhoriz.-vert) 20 ,0.9 I.3 0.7l 0.,7 0.7nUOia=traom re..re.s~slOn .Norm~al =linput vaiue' ,rucs =caicuiateoarrom orner values. -.. .. ..YVolumne above breachblottom (acre-feet) 1 ...... 1 1 ,117,818:!.Triangular breach formation times (hours) -1. .:" .,.14.013.012.011.010t.07.05.04.03.02.01.0I.* , ,-4 7].. ._ .Height of Height ofbreach- breach-Revise.d Xu Froehlich& Zhangtime -Revised Xu& ZhangFailure Breach top Breach top. Averagetine,- width -width. breachuFro ehllch Revised Xu Froehllch width -& Zhang Revised KU*& ZhangBreac:h P'arameter.- Regression MethodologyAveragebreach*width FroehlichPeakoutflow-RevisedXu&ZhangPeakoutflow -FroehllchFigure 7.1. Relative width of Confidence intervals for the revised Xu and Zhang andFroehlich (1995a and 2008) breach parameter estimates for Jocassee Dam expressed asa ratio to the median estimate (ratio = 1.0).(1995b and 2008). The confidence bounds for the revised Xu and Zhang regression equationsrare wider than those for FroehliCh (2008) due tO the smaller number Of case histories thatremained in the revised Xu and Zharng data set. !nterestingly° there are other case histories withobserved values of failure time that included in Froehlich (2008). but which are not included inP AGE 33' I[..flflfrfl R r'_lfl__ _. _ aNrm]']f .arl~ljra -in.I/I.] E ~ .~~~l ]I :;m....: ..z .T5 f li U .sv v vw vW 7 # ## Villi -*VALIDATION OF HRR BREACH HYDROGRAPH FOR JOCASSEE DAMthe original or revised Xu and Zhang data set. We could have added these but our focus wason workinlg With those that Xu and Zhang (2009) had originally used rather thanl adding newcases.The median estimate for the breach bottom elevation of 848 feet msl. (and: hence an estimatedheight of the breach of 277 feet) predicted by the revised. Xu and Zhang method is very similarto the assumed value of 850 feet msl. (and hence an estimated height of the breach of 275 feet)that We independently estimated in our application of the Froehlich (2008) method since that~method does not predict this .breach parameter. We .based that estimate on the expectation thatthere would be significant deposition of. material immediately below the darn that would limit thedownward breach development. This position is consistent with the. experimental tests on therockffll dam breaching process by Franca and Almeida-(2002), which showed that "the.deposition of the rock blocks: immediately downstream, of the dam has a stabilizing effect,sustaining, the, failure process -this is reflected mainly on the final breach depth which is about80% of the dam height." In addition, many embankment dam failures case histories documentthat breaches less than the full dam height have occurred. However, since so few rockfill damshave failed, the experimental work of Franca and Aimeida (2002) is probably the .best indicationof the reduced breach depth associated with a rockfilll dam failure due to deposition immediatelydownstream of the breach.It is noted that a breach bottom elevation of 850 feet msl. corresponds to releasing about 96%.of the reserVoir contents below the initial normal full pool at Elevation 1,110 .feet msl. Thiscompares with about 96.5% of the reservoir 'contents- below Elevation 1,110, feet msl. for" abreach bottom at Elevation 848 feet rnsl., which was predicted using the revised Xu and Zhangregression equations that was used in the sensitivity studies. For the original Xu and Zhang(2009) regression equations, .which were used as the basis for the HRR breach hydrograph(Duke 2013), the predicted breach bottom elevation of 870 feet msl. corresponds releasing94% of the reservoir contents below Elevation 1,110 feet msl.An additional sensitivity case is described at the end of Section 7.4 in which the breach bottomelevation was set to Elevation 800 feet msl. and, all the other breach parameters were keptidentical to those used forrthe HRR breach hydrograph (Duke 2013). Even though this run wasperformed in a conservative manner, it was cconclUded that-.a lower breach bottom-does notsignificantly change the. breach. hydrograph.The largest difference between estimates from the revised Xu and Zhang and Froehlich (1995ban 2008) methods is for the average breach width and as a result of that, the side slopes. Theaverage side slope, value of 0.7 was assumed in our application of the Froehlich (2008) method.following a recommendation by Froehlich (2008), whereas the larger values from the revised Xuand Zhang method are predicted Values. As described below in/Section. 7.4, where thesedifferent median values were usedrby HDR in the HEC-RAS model there is some effect on the:breach hydrograph shape due to the different breach cross-sectional areas, but not on the peakp A GE 34v VALIDATION OF HRR BREACH HYDROGRAtPH FOR JOCA-SEE DAMbreach flow rate since it is determined by matching the median values for peak outflowpredicted by the-resPective methods..Returning to the estimated median breach formation times from the revised Xu and Zhang andthe Froehlich (1995a and 2008) methodologies, we conducted a- simple check on thereasonableness of these predicted times and their consistency with. the..predicted peak outflowrates and Volume of the reservoir contents above the breach bottom elevation. The .checkinvolved assuming that the breach outflow hydrograph has a triangular shape with the base ofthe 'triangle representing the breach formation time, the height the peak outflow rate, and thearea of the triangle the volume of reservoir contents above the breach bottom elevation. Underthis assumption ani approximate breach fOrmation. time can be calculated from simple geometrybased on Equation 6, which is presented in Section 6.2.8.The breach formation times estimated from Equation 6 are given at the bottom of Table 7.1.These times, are clearly much longer than those obtained from both the revised Xu and Zhangand the Froehlich (1 995a and 2008) regression m ethodologies. The sources of these significantinconsistencies in breach formation time estimates for Jocassee Dam, are believed to include,the following:*, Inconsistencies between case history estimates of observed breach times, peak outflowrates and .volumes of the reservoir contents above the breach bottom elevation in theWahl (1998), Froehlich (1995b and 2008),and Xu and Zhang ,(2009) data sets (seeSection 6.2..8)* The breach formation time is apparently not well represented by the regression equationmethodologies for the large volume of the contents of Lake Jocassee above the breachbottom, which at the normal maximum reservoir level is about twice the volume of waterfor .the case history with the largest reservoir breach rvolume (Oros, Dam) and about fourtimes the corresponding volumes for the Teton Dam breach (see Figure B.la).The HEC-RAS simulation model predicts a breach hydrograph with a volume equal to thereservoir Contents above the breach bottOm elevation. Iln such a simulation it would beimpossible to match both the predicted values of breach formation times and peak outflow ratefrom either the revised Xu and Zhang or the Froehlich (1 995a and 2008) regression methodsbecause the predicted breach formation. time from the regression methods is too short torelease the reservoir, contents.. This 'is illustrated for the Safety Evaluation (SE) (NRC 2011)breach hydrograph for Jocassee Dam in Section 7.3.Therefore it is clear that both regression methods underestimate the breach formation time forthe large volume reservoirs such as Lake Jocassee. To address this shortcoming wedeveloped an adjustment through following procedure, which is described below for the revisedXu and Zhang methodology with references to Figure 7.2:P A 6E 35'I)

r, ~X..JLt-; Lfonzgzc ~AWi.tz!d him wrtft tffm'2cr ,jrrw I" {7C0 )In association with 1t44~~3VALIDATION OF HRR BREACH HYDROGRAPH FOR JOCASSEE DAMob)(7)(F)Figure 7.3. Distributions of predicted peak breach outflow rate and breach development time -Froehlich (1995a and 2008)P A GE 36

~VALIDATION OF HRR BREACH HYDROGRAPH FOR JOCASSEE DAM, 'The entire probability distribution representing estimation uncertainty for predicted peakbreach outflow rate was developed from the 1 = through the 99th percentiles using thesame equation that was used to calculate the upper and lower bounds by assigning thevalue of the Student t statistic corresponding to each percentile (left plot in Figure 7.2).* The distribution, of predicted peak breach outflow rate (left plot in Figure 7.2) wastransformed to a distribution of breach formation times (right plot in Figure 7.2) usingEquation 6 based .on the triangular breach hydrograph approximation applied to eachpercentile.*Calculate a mean breach formation time needed to release the reservoir contents fromthe distribution of breech formation times (right plot in Figure 7.2). This was calculatedto be cb)(7)(F) I(see the blue dot-dash line on right plot in Figure 7.2), whichcorresponds to about the 34th percentile.*Obtain ,the mean peak breach outflow rate that is consistent with the mean breachformation time needed, to release the reservoir ,contents using the triangular breachhydrograph aporoximation .- that is. cor~responding to the 34th percentile. This wascalculated to bel~)()(F J Icfs (see blue dot-dash line on left plot in Figure 7.2).The mean breach formation time Iwas used in HEC-RAS as the time betweenpoints B and D as defined on Figure B.4 (see also Figure 7.5 in Section 7.4) together with themedian estimates of the breach geometry from the reVised Xu and Zhang methodolog.j-HEC-RAS was then run to approximately match the mean-peak breach outflow rate ofb)7)f) cfsby iteratively changing the values of the orifice arid weir coefficients and the breach progressionrelationship as described in Section 8.6.The above-adjustment procedure for addressing the shortcoming with the predicted breachformation time was also applied to the Froehlich (1995a and 2008) methodology. The mean breach formation time needed to release the reservoir contents was calculated to be LZF")'(b()()(see the green do~t~Ish .line ojn right plot in Figure 7.3) and the corresponding mean peak*breach outflow rate j cfs. both of which are at about the 40O~ percentile on theirrespective probability distributions.The adjustment described above relies on the relatiVely precise knowledge Of the volume of thereservoir contents above the breach bottom elevation and the predicted values of the peakbreach outflow rate, which' of all the breach parameters have the highest R2 valUes for both therevised Xu and Zhang methodology (R2 = 81%) and the Froehlich (1995a and 2008)methodology (R2 = 93%).Table 7.2 contains a comparison of the breach parameter values used to develop the breachhydrographs in the Safety Evaluation (SE) (NRC, 2011) (discussed in Section 7.3), the HRR(Duke 2013) (discussed in Appendix B.6) and the two 'sensitivity studies (discussed in Section7,4). Table 7.3 contains the comparison of estimated Jocassee Darn peak breachu ij ill : iP AGE 37, tv.,,u;,oii-p , .;,o';u .u.a -vvninnumg ,'urn puu'Ic uisvwsure per iv Z.JIuOIJS nassociaion with RA CVALIDATION OF HRR BREACH HYDROGRAPH FOR JOCASSEE DAMiiii t l t ii wTable 7.2. Comparison of breach parameter values used in the Safety Evaluation (SE)(NRC 2011), the HRR and the Sensitivity studiesSJanuary 2011 3/12/2013Sestvy- SnititBreach Safety Hazard Renstvise yX an Srehsithi(1ityPrmtr Evaluation (SE) Reevaluation -Reviad g and 2008)ch(195Parameter (NRC 2011) -Xu and Zhang anad208_________ Froehlich (2009)Figure No. forbreach 7.4 B.5 7.5 7.6hydrographs ________ _______Top Width (feet) 1,156 701 1,009 1,082BotmWdh425 431r 277 696(feet)Bottom Elevation80878485(feet msi.) ____00____ ____70____ 848_______ ____50__(.)(7)(F)BreachFormation Time(without pipingphase) (hou rs)Peak OutflowRate (million cfs)Side Slopes Right: 1.55, Left: Rig ht: 0.53, Left: vrg .vrg .(horiz:vert). 0.7 .0.53 Aveag 1.3 Avrg .P A.6 E 38, Coninins -.In.rirnaton. -vvnnuiu nwm, gin. .u a----- -----.I--,rJ Wv.--.W ..... , ...... .Fv ................ W ..... ................. .....VALIDATION OF HRR BREACH HYDROGRAPH FOR JOCASSEE DAMTable 7.3. Comparison of Estimated Jocassee Dam Peak Breach Outflow Rates providedin the Safety Evaluation (SE) (NRC 2011)Model Peak Outflow (cfs)McDonald & Langridge-Monopolis (1984) IX)FCosta (1 985)Evans (1986)scs (1981)Bureau of Reclamation (1982)McDonald and Langridg e-Monopolis (1984) ____________________outflow rates from several regression methodologies that was provided in the Safety Evaluation(NRC 2011).Table 7.4 summarizes the basis for each breach parameter estimate used in the sensitivitystudies that are discussed in Section 7.4. In all cases they are the mean or the moreconservative median estimate of the breach parameters. In our FebruarY 201.3 report (Ehaszand Bowles 2013). we concluded that the use of median values of the breach parameterestimates for Jocassee Dam would be a conservative ,choice. We argued that in reality wewould expect that the peak breach flow. rate for Jocassee Dam to be in the range between themean and lower bound confidence interval estimates, which is the range in which the peakbreach flow rates fall for both the adjusted revised Xu and Zhang and the adjusted Froehlich(1 995a and 200.8) methodologies. The reasons for expecting the peak breach flow rate forJocassee Dam to be in the range between the mean and lower bound confidence intervalestimates include the fact that Jocassee Dam was designed and constructed as a modernrockfill dam such that it would be expected to be a more resistant dam to the breach processthan other low erodibility dams for which failure data were used to develop the revised Xu andZhang and Froehlich (1995a and 2008) methodologies. In addition, the uni-directional breachformation starting at the right abutment and the downstream deposition of rockfill materialTable 7.4. Summary of the basis for each breach param eter used in sensitivity studiesBasis for estimate used in sensitivityBreach Parameteranlss_______Peak Outflow, Q Mean ConservativeBreach development Mean Conservative Consistent withtime, T Qp& VBreach depth, Hd Mean ConservativeBreach top width, Bt Median (> M ean) ConservativeBreach averagewidth, B Median (> Mean) ConservativeP A GE 39v am I--. *lISIn association withRAVALIDATION OF HRR BREACH HYDROGRAPH FOR JOCA5SEE DAMleading to development of tailwater during breach formation also support the peak breach flowrate for Jocassee Dam to be in the range between the mean and lower bound confidenceinterval estimates. Mohamed (2002) demonstrated that a "side breach" results in a significantlylower peak breach flow rate and narrower width than a "center breach" in simulations ofthe Teton Dam failure.7.3 Example of Inconsistencies between Peak Breach Flow and BreachDevelopment TimeFigure 7.4 contains the Jocassee Dam breach hydrograph for the breach Case 2(100W) insupport of the Safety Evaluation (SE) (NRC 2011) based on a HEC-RAS simulation. TheJocassee headwater hydrograph is represented by the blue line (left scale

1000), theJocassee tailwater hydrograph is represented by the brown line (left scale

1,000) and theJocassee breach discharge hydrograph is represented by the green line (right scale) at alocation immediately downstream of the internal boundary in HEC-RAS model that representsthe Jocassee Dam. The assumed sinusoidal form for the breach progression relationship isshown by the black line (left scale).The peak breach flow rate for the Safety Evaluation (SE) (NRC 2011) hydrograph shown inFiue7.4 is abo cfs for the SE hydrograph based on using a breach formation timeFigure 7.4. Jocassee Dam breach progression relationship and breach hydrographsbased on the breach Case 2(100W) in t he Safety Evaluation (SE) (NRC 2011)P A GE 40 l P In association., w VALIDATION OF HRR BREACH HYDROGRAPH FOR JOCASSEE DAMm i .pand median breach geometry parameter estimates based on Froehlich (1995a).The inconsistency between the peak breach flow rate and the breach development time for theSE breach hyrgahis cleanl seen in Figure 7.4 because the breach progression *relationshipreaches 100% aftep(7)(Fj j which implies that the breach develgpment is~ complete at thattime. However, at this time the simulated breach flow rate is abouJ~b)(F)F Jcfs. The breachsize certainly would not have stabilized at such a large flow rate and would be growing quiterapidly. If a more realistic and longer breach development time, consistent with emptying thereservoir had been used the rate would have been, much smaller (thebreach time ~would need to be longer thatq' "Jas in the S E hydrograph and the peak outflowrate of[ L)(TF) ......Jcfs would decrease for a longer breach time). This type of physicalinconsistency is determined by the underestimation of the breach development time that is inputto HEC-RAS based on the estimate from Froehlich (1995b)3.The HEC-RAS model does notsimulate the physical erosion and instability processes that would take place in an actual breachand therefore the model has no way to assure a consistent simulation unless a consistent set ofbreach parameters are input to the model. Achieving this consistency is the purpose of theadjustment that is described in Section 7.2 to account for the *time required to completely emptythe Jocassee reservoir and which is applied in the sensitivity analyses presented in Section 7.4.7.4 Discussion of HEC-RAS ResultsFigure 7.5 contains the breach hydrographs developed by HDR using HEC-RAS based on thebreach parameters estimated from the adjusted revised Xu and Zhang regression equationswith the Froehlich breach development time definition and the Chinese case histories excludedas summarized in Section 6.3.2. Figure 7.6 contains the breach hydrographs based on thebreach parameters estimated from the adjusted Froehlich (1 995a and 2008) regressionequations. The predicted values of peak breach outflow rate and breach development time forboth the revised Xu and Zhang and the Froehlich (1 995b and 2008) methodologies aretherefore the mean ,eStimates obtained using the adjustment as described in Section 7.2 toaccount for the time required to completely empty the Jocassee reservoir (see Table 7.4). InFigures 7.5 and 7.6, the Jocassee headwater hydrograph is represented by the blue line (leftscale

1000), the Jocassee tailwater hydrograph is represented by the brown line (left scale'*1,000) and the Jocassee breach discharge hydrograph is represented by the green line (rightscale) at a location immediately downstream of the internal boundary in HEC-RAS model thatrepresents the Jocassee Dam.The breach progression relationship, which is a required HEC-RAS input, and which wasdeveloped iteratively as described in Section 7.2, is shown by the black line (left scale). PointsA, B and D are equivalent to points that are defined in Figure 6.4. The final values of the orifice3 A similar underestimation of breach development time has been identified in Section 7;2 for Xu and Zhang (2009).P AGCE 42.

,JR Ina +oton withVAUIDATION OF HRR BREACH HYDROGRAPH FOR JOC.ASSEE DAMpFigure 7.5. Jocassee Dam breach progression relationship and breach hydrographs -sensitivity run using revised Xu and Zhang breach parameter estimatesD:)fTj(F)Figure 7.6. Jocassee Dam breach progression relationship and breach hydrographs -sensitivity run using Froehlich (1995b and 2008) breach parameter estimatesP A GE 42 VALIDATION OF HRR BREACH H VDROGRiAPH FOR JOCASSEE DAMcoefficients of 0.1 for both the adjusted revised Xu and Zhang and the adjusted Froehlich(1995a and 2008) breach parameter estimates appear to be reasonable in terms of representinga piping flow through the rockfill material. Similarly, the final values of the weir coefficients 2.2and 2.0 for the adjusted revised Xu and Zhang and the adjusted Froehlich (1995a and 2008)breach~parameter estimates, respectively, appear to be reasonable in terms of representing flowthrough the breach following .collapse of ther dam crest of the rockflll dam.In addition, the form of the resulting breach hydrographs Shown in Figures 7.5 and 7.6 alsoappear to be reasonable for a piping failure mode and closely match the mean peak breach flowrate estimates obtained for the adjusted revised Xu and Zhang and the adjusted Froehlich(1995a and 2008) methodologies,.respectively. Point A represents the beginning of the HEC-RAS simulation of the enlargement of the pipe. The breach progression curve was adjusted tokeep the flow rate to a reasonably low magnitude prior to the collapse of the pipe and the onsetof overtopping that is simulated at point B on Figures 7.5 and 7.6. These points mark the end ofthe breach initiation phase as defined in the revised Xu and Zhang methodology, which isconsistent with the definition used by Froehlich (1 995b and 2008) and Wahl (2013). Point D onFigures 7.5 and 7.6 marks the end of the breach development phase. The times betweenpoints B .and D in Figures '7.5 and 7.6 are approximately equal to the mean breach developmenttime estimated using the adjustment described in Section 7.2 for both the revised Xu and Zhangand Froehlich (1 995a and 2008) methodologies, respectively.When Compared with the breach hydrographs from the HRR (Duke 2013), shown in Figure B.5,we conclude that. the breach hydrographs in Figures 7.5 and 7.6. which are based on theadjusted revised Xu and Zhang and the adjusted Froehlich (1 995a and 2008) breach parameterestimates, respectively, provide good support for the HRR breach hydrographs (Duke 2013). Inour February 2013 (Ehasz and Bowles 2013) we concluded that the breach hydrograph inFigure B.5 is a realistic but conservative breach hydrograph that has good defendablity basedon the validity of the Xu and Zhang (2009) method, the conservative nature of the medianbreach~parameter estimates, a piping failure mode initiating in Jthe deposition'of rockfill immediately below the dam, the low erosion category of the rockfill material, and thevarious characteristics of a modern dam that were included in the design and construction ofJocassee Dam.An additional sensitivity case was considered in which the breach bottom .elevation was set to,Elevation 800 feet nmsl, corresponding tO 99.4% of the reservoir contents below the initial normalfull pool at Elevation 1,110 feet msl, and all the other breach parameters were kept identical tothose used for the HRR breach hydrograph (Duke 2013), including the breach progressionrelationship. The resulting hydrographs are presented in Figure 7.7 using the same format asused in Figures 7.4, 7.5, 7.6 and B.5. The effects of the. lower breach bottom elevation, can beseen by comparing the results in .Figure 7.7 with those in Figure B.5 for the HRR breachhydrograph in which the breach bottom elevation was at Elevation 870 feet msl, which is theP A 6E 43 tISIn association with JVALIDATION OF HRR BREACH HYDROGRAPH FOR JOCASSEE DAMFigure 7.7. Jocassee Dam breach progression relationship and breach hydrographs -sensitivity run using breach bottom elevation of 800 feet msl. and all other breachparameters identical to those in the HRR breach hydrograph (Duke 2013) based on Xuand Zhang (2009)estimate based on Xu and Zhang (2009), and which corresponds to 94:1% of the reservoircontents below the initial normal full pool at Elevation 1,110 feet msl. In the simulation theadditional reservoir contents is released mainly on the falling limb of the hydrograph resulting inhigher flows for much of the falling limb starting with a somewhat flat portion of the hydrographfollowing the peak flow rate. Although it is considered that a more realistic simulation of thelower breach bottom would tend to lengthen the falling limb rather than raising it, we view thissimulation, in which the breach development time was constrained to match the time used in theHRR hydrograph, as a conservative case in terms of the effects on the downstream flowconditions. Therefore a more realistic simulation was not pursued and it was concluded that alower breach bottom would not significantly change the breach hydrograph even under theconservative sensitivity case summarized above.The discussions in Appendices C.1 and C.2 benchmark the characteristics of several recentlarge embankment dam failures. They also describe the properties and failure conditions aswell as embankment design considerations affecting these breaches and their relevance to theJocassee Dam.PAG0E 4 lI S in association with VALIDATION OF HRR BREACH HYDROGRAPH FOR.JOCASSEE DAM

8.0 CONCLUSION

S8.1 Discuss Overall ConclusionThe overall conclusion of this report is that the HRR breach hydrographs (Duke 2013), whichwas based on the original Xu and Zhang (2009) breach parameter regression equations, is areasonable and conservative estimate of the downstream effects of a deterministic sunny-daybreach of the Jocassee Dam. This conclusion is supported by our review of the data on whichthe Xu and Zhang (.2009) methodology is based, the confirmation of the assignment of a lowerosion category to Jocassee Dam, and by comparisons with two additional breach hydrographsthat are based on the Froehlich (1995a and 2008) regression equations and the revised Xu andZhang regression equations in which the agency questions about the original Xu and Zhang(2009) methodology have been addressed. Both the revised Xu and Zhang and Froehlich(1 995a and 2008) methodologies have been adjusted to allow for sufficient time to drain LakeJocassee down to the breach bottom elevation (see Section 7.2)The specific conclusions for this report are organized into two parts. In Section 8.2 wesummarize our conclusions regarding our responses to the five agency questions. In Section8.3 we summarize our conclusions from the review and revision of the Xu and Zhang (2009)methodology and the support that its application and an application of the adjusted Froehlich(1995b and 2008) methodology, to Jocassee Dam provide for the HRR breach hydrographssubmitted to the NRC by Duke (2013).8.2 Concluding Responses to Agency Questions1) Precedence: Several uses of the Xu and Zhang (2009) ;methodology have beenidentified in addition to its application to Jocassee Dam. This new methodology seemsto be following a pathway to broader acceptance in which its significant advantage overother methods by accounting for the important physical characteristic, Of erodibility isbecoming recognized. The initial questions about the methodology are beingaddressed, including how to appropriately define and apply failure time estimates in dambreach modeling.2) Chinese case histories: About 43% of the 75 dam failure case histories on which theXu and Zhang (2009) methodology is based are for Chinese dams. Our review indicatedthat Xu and Zhang (2009) did appropriate screening and interpretation of the casehistory data from all sources, including China; although we identified a fewimprovements [see 2 in Section 8:3 belowj. The quality of data for the Chinese casehistories appears to be similar to that available for US case histories with more recentbreaches; although access to some of this data has been limited outside of China. Thepoorer construction of Chinese dams built prior to 1977 would be expected to, result in amore erodible dam once a breach process has initiated. This was appropriatelyP A GE 45 VALIDATION OF HRR BREA CM HYDROGRAPH FOR JOCASSEE DAMaccounted for by assigning a higher erosion category in the Xu and Zhang (2009)3) Representation of case histories for rockfill and other low erodibility dams: Thesmall number of case histories for rockfiUl dams that are classified with low erodibility is areality that is likely due to the intrinsic safety of such rockfill dams. This limitation appliesto all regression methodologies. However, the inclusion of the Briaud (2008) erosioncategories as a control variabl e in the Xu and Zhang (2009) methodology provides a wayto account for the important* influence of the erodibility of materials on breachparameters. Also, Xu and Zhang (2009) increased the number of case histories byincluding case histories from China for the Danghe and Gouhou large ro ckfilI dams.4) Use of the Briaud erosion categories: Professor Briaud's independent reviewconfirmed the following:! Theappropriateness of using his erosion categories in the Xu and Zhang (2009)methodology.* The Xu and Zhang (2009) two-step procedure for assigning low, medium or higherosion categories to case history dams is consistent with' his research findings:i) an initial categorization as a range based on the soil type within the dam as lowto medium erodibility for rockfill and clay and medium to high erodibility for silt,,and sand; and ii) an up or down adjustment in the initial range based onconstruction quality, particularly compaction effort, that, is dePendent mainly onthe period of construction but also dam cross-sectional geometry and slopesurface protection. In a few cases erosion categories were changed assummarized in 2 in Section 8.3 below.* The assignment of a low erosion category for Jocassee Dam was confirmedthrough a conservative analysis of the erosion rates for cross-section materialsbased on both velocity and shear stress.5) Breach time definition: The definition of breach time used by Xu and Zhang (2009)includes both a part of the breach initiation process in addition to the breach formationprocess unlike other regression methods (e.g. Froehlich 1 995b and 2008) that includeonly the latter. We found that this difference in definitions is of no concern as long as itis appropriately accounted for in using the predicted breach time in a way that isconsistent with the HEC-RAS model definitions.8.3 Concluding Support for the HRR Breach Hydrograph1) Agency Concerns: Our review of the agency questions (summarized in Section 8.2)indicates support for the original application of Xu and Zhang (2009) tO estimate breachparameters on Which the HRR breach hydrographs are based; although someimprovements to the Xu and. Zhang (2009) data base w ere identified [see 2) below]..P AGE 46 SIn association with VALIDATION OF HRR BREACH HYDROGRAPH FOR JOCASSEE DAM2) Revised Xu and Zhang regression equations sensitivity studies: The revisedregression equations were developed by Dr. Xu based on the following changes andimprovements to the XUi and Zhang (2009) data set:*Changed breach development times to the commonly-used Froehlich (1995b and2008) definition. This change was seen as a way to predict the duration o~f thebreach hydrograph in HEC-RAS; but, as summarized in 3) below, a broaderissue with inconsistent "observed" breach times was found that required anotherstep to obtain a reasonable predicted dur ation.* Changed the values of other breach param eters and control variables where theywere inconsistent with the Wahl (1998) and FroehliCh (1995a and' b and 2008)data sets with consideration given to reliable information from other, sources.* Changed some assigned erosion categories to include the consideration thatcompaction associated with construction practices in the US and other developed.countries (not China) improved for earthf ill dams after about 1950 and for rockfihtdams after about 1965.* Changed to a higher erosion category where a lower category had beenassigned because of long observed failure times but where all other availableinformation pointed to the higher erosion category.' Embankment dams with a core wall or concrete-faced dams that had beenassigned to the low erosion category as a means of accounting for the throttlingeffects of these features on breach development were omitted from the reviseddata set because their breach parameters would not be representative of lowerodibility embankment dams in general.* All Chinese case histories were omitted from the revised data set to avoid thepotential criticism that we only had indirect access to the original references forthese case histories.3) InConsistencies between peak breach flows and breach development times: Aninconsistency was identified for many case histories in the WahI (1998), Froehlich(1 995a and b and 2008), and XU and Zhang (2009) data sets. Specifically, the;'observed" breach development time is too short to discharge the reservoir contentsabove the breach bottom and match the "observed" peak breach flow rate. Thisinconsistency can be clearly seen in the Jocassee Dam breach hydrograph submitted tothe NRC by Duke in support of the Safety Evaluation (E) Report (NRC 2011t) (Figure7.4) that is based on using a breach formation time oti~b)(j(F .and median breachgeometry parameter estimates~dFroehlich (1995a). The breach progressionrelationship reaches 100% aftetiI'jJ Iwhich implies that the breach .evelopment iscornplete at that time. However, the simulated breach flow rate is about 'j)7)F) /cfs at[()7)(F) Jand therefore the breach size certainly would be growing quite rapidly. A morerealistic simulation would require a longer breach development time that would producea smaller peak breach outflow rate. To address this shortcoming .an adjustment wasP AG6E 47 VAUIDATION OF HRR BREACH HYDROGRAPH FOR JOCA SSEE DAMdeveloped to obtain an estimate of the mean peak breach flow rate that is consistentwith the mean breach formation time forea triangular breach hydrograph with a volumeequal to the reservoir volume above the breach bottom (detailed in Section 6.2.8). Thisadjustment was also applied to the Froehlich (1 995a and 2008) methodology toovercome the same shortcoming [see 5) below]. The adjustment relies on the relativelyprecise knowledge of the volume of the reservoir contents above the breach bottomelevation and the predicted values of the peak breach outflow rate, which of all thebreach parameters have the highest R2 values for both the revised Xu and Zhangmethodology (R2 = 81%) and the Froehlich (199 5a and 2008) methodology (R2 = 93%).4) Application of Revised Xu and Zhang regression equations to Teton Dam: Therevised best exact and best simplified Xu and Zhang equations were applied to theTeton Dam. The median predicted values for the high and medium erodibility categorieswere averaged, based On an evaluati on by Professor Briaud that Teton Dam erodibility ison the boundary between the high and medium erosion categories. The percentdifferences between the observed and predicted breach parameters were smaller formost breach parameters compared with those obtained using the original Xu and Zhang(2009) equations. An attempt to evaluate the adjustment procedure for accounting forthe inconsistency in predicted breach time summarized in 3) above was found to beproblematic because the observed breach time for the Teton Dam is uncharacteristicallyshort due to an unusually sudden breaCh mechanism caused by the large internal void,which has been documented by the Bureau of Reclamation cause evaluation (Osmun2013).5) Sensitivity of the Jocassee HRR Breach Hydrograph based on Adjusted RevisedXu and Zhang Equations and Adjusted Froehlich (1995a and 2008): Considering thewidths of the confidence intervals for both methods, both methods provide fairly similarmedian and mean estimates. Specifically with the adjusted revised best exact Xu andZhang methodology, which uses the same breach formation time definition as Froehlich(1995b and 2008),1.and the adjusted Froehflch l995b the meanbreach formation time estimates arep I( l Jand I Ij respectiveiy. Byiteratively changing the orifice and weir coefficients and the breach progressionrelationship~ as rUn match the mean peak breach flow rateestimates oli"j )W " cfs .. Ifs, for the two methodologies respectivelY.The resulting breach hydrographs obtained by HDR forea deterministic piping failure ofJocassee Dam are similar to the HRR breach hydrograph (Duke 2013). It is thereforeconcluded that the use of the adjusted revised Xu and Zhang and the adjusted Froehlich(1995a and 2008) provide additional support for the conclusion in our February 2013report (Ehasz and Bowles 2013) that the HRR breach hydrographs are realistic butcOnservative breach hydrographs that have good defendeblity based on the validity ofthe Xu and Zhang (2009) method, the conservative nature of the mnedian breachparameter ((7F)estimates, a piping failure mode initiating in the [(,~ Iresulting in abreach developing in a single direction towards the center of the dam, the deposition ofrockfill immediately below the dam, the low erosion category of the rockfill material, thepP A GE 48v VALIDATION OF HRR BREACH HYOROGRAPH FOR JOCASSEE DAMvarious characteristics of a modern dam that were included in the design andconstruction of Jocassee Dam and the time required to drain Lake Jocassee to thebreach bottom elevation.6) Sensitivity of the Jocassee HRR Breach Hydrograph to a Lower Breach BottomElevation: A sensitivity run was performed with the breach bottom elevation set toElevation 800 feet msi. instead ,of Elevation 870 feet' msl., but with all the other breachparameters unchanged from the HRR breach hydrograph (Duke 2013). Even thoughthis run was performed in a conservative manner, it was concluded that a lower breachbottom would not significantly changethe breach hydrograph.P AG6E 49w

.... .. .. .. ..- --n ..-l--,drVALIDATION OF HRR BRF.A C II YDROGRA PH FOR.JOCASSEE DAM

9.0 REFERENCES

Bureau of Reclamation. 1982. Guidelines for defining inundated areas downstream fromBureau of Reclamation dams. Reclamation Planning Instruction Rep. No. 82-11, U.S.Dept. of the Interior, Bureau of Reclamation, Denver.Bureau of Reclamation. 1988. Downstream hazard classification guidelines. ACER Tech.Memorandum Rep. No. 11, U.S. Dept. of the Interior, Bureau of Reclamation, Denver.Briaud, J. L. 2008. Case Histories in Soil and Rock Erosion: Woodrow WilsOn Bridge, BrazosRiver Meander, Normandy Cliffs, and New Orleans, Levees. Journal of Geotechnical andGeoenvironm ental Engineering, 134 (10): 1425-1447.Briaud, J. L. 2013. Jocassee Dam. Report to URS. October 22. (Appendix A of this report)Brunner, G.W. 2011. Hydraulic Model Development for Dam Break Studies. HydrologicEngineering Center, U.S. Army Corps of Engineer~s. March.Costa, J.E. 1985. Floods from Dam Failures. U.S Geological Survey Open File Report 85-560,Denver, Colorado. 54p,Duke Energy Company. 2013. Hydrologic Reevaluation Report submitted to the NRC onMarch 12, 2013.Ehasz, J..L. and D.S. Bowles. 2013. Jocassee and Keowee Dams Breach Parameter Review.Report for Duke Energy by URS Civil Construction & Mining and RAC Engineers &Economists. February.Evans, S. G. 1986. 'The maximum discharge~ of outburst floods caused by the breaching ofman-made and natural dams. Canadian Geotechni cal Journal, 23(4) :385-387.Fell, R., Wan, C.F., Cyganiewicz, J. and Foster, M. 2003. Time for Development of InternalErosion arid Piping in Embankment Dams. Journal of Geotechnical andGeoenvironm ental Engineering, 129 (4):307-3 14.Franca, M.J. and A.B. Almeida. 2002. Experimental tests on rockfill dam breaching procpss.Proc. Intern. Syrup. on Hydraulic and Hydrological Aspects of Reliability and SafetyAssessment of Hydraulic Structures, St. Petersburg, Russia.P A 6E 50 uoL:zr...-:- ra..: .~fn~r~o /tf ' JInptJc cer- r N --.Y .... -- -- --VALIDATION OF HRR BREACH HYDROGRAPH FOR JOCASSEE DAMFroehlich, D.C. 1995a. .Embankment* dam breach parameters revisited. Proc., WaterResources Engineering, 1995 ASCE Conf. on Water Resources' Engineering, ASCE,NY, 887;-891.Froehlich, DC. 1995b. Peak outflow from breached embankment dam. J. Water Resour.Plann. Manage., 121(1):90--9 7.Froehiich, D.C. 2008. Embankment Dam. Breach Parameters and Their Uncertainties. Journalof Hydraulic .Engineeding, 134(1 12):1 708-1721.Haan, C.T. 1977. Statistical Methods in Hydrology. iowa State University Press.HR Wallingford. 2012. AREBA (A Rapid Embankment Breach Assessment), Breach size -rapid methods of assessment. http://www.hrwallingford.comlproiects/breach-size-rapid-methods-of-assesSment. Accessed January 26, 2014..HR Wallingford. 2014. Small Reservoirs Simplified Risk Assessment Methodology: ResearchModelling Report. Final report to Defra and Environment. Agency Flood ,and CoastalErosion Risk Management Research and .Development Programme, Project FD2658.January.MacDonald, T.C., and J. Langridge-Monopolis. 1984. Breachi~ng characteristics of damfailures. J5. Hydraul. Eng., 110(5):567-586.Mohamed, M.A.A. 2002. Embankment breach formation and modelling methods. The OpenUniversit, England, UK.. April.Nuclear Regulatory Commission (NRC). 2011. "Staff Assessment of Duke's Response. toConfirmatory Action Letter .Regarding Duke's Commitments to Address ExternalFlooding Concerns at the Oconee Nuclear Station, Units. 1, 2, and .3 (ONS) (TAG Nos.ME3065, ME3066, and ME3067)". January 28.Osum, D. 2013. Teton Dam Failure:: A Review* of the Technical Factors Contributing to theFailure.. Presentation to the Ass ociation of Engineering Geologists. May.Reclamation-USACE-URS-UNSW. 2008. Piping* and Seepage Toolbox.Soil Conservation Service. 1981. Simplified dam-breach routing, procedure. U. S. Departmentof Agriculture, Technical Release 66, Washington,. D.C., 25 p. plus appendix.Singh, VP. 1996. Dam breach modelling technology. Kluwer Academic, Boston.P A GE 51-VALIDATION OF HRR BREACH HYDROGRAPH FOR JOCA SSEE DAMRu, N.H. and Y.G. Niu. 2001. Embankment dam -incidents and safety of large dams. WaterPower Press, Beijing. [in Chinese.]Sowers, G.F. 1987. Jocassee Main Dam Design, Construction and Performance. Report toDesign Engineering Departm ent, Duke Power Company, Charlotte, North Carolina. April.Von Thun, J.L., and D.R. Gillette. 1990. Guidance on breach parameters. InternalMemorandum, U.S. Dept. of the Interior,. Bureau of Reclamation, Denver.Wahi, T. L. 1998. Prediction of Embankment Dam Breach Parameters -A Literature Review andNeeds AssesSment. Dam Safety Report No. DSO-98-004, U.S. Department of theInterior, Bureau of Reclamation, Denver, Colorado.Wahi, T.L. 2004. Uncertainty of Predictions of Embankment Dam Breach Parameters. ASCEJournal of Hydraulic Engineering, Vol. 130, No. 5, May 1.Wahl, T.L. 2012. Several verbal discussions with J.L. Ehasz regarding the use of the Xu andZhang (2009) technical paper as well as verbal discussions of erodibility factors asrelated to rockfill dams.Wahl, T.L. 2013. Incorporating Breach Parameter Estimation and Physically-Based DamBreach Modeling into Probabilistic Dam Failure Analysis. Presented at the NRCInteragency Workshop on Probabilistic Flood Haz ard Assessment. January 30.Walder, J.S., and J.E. O'Connor. 1997. Methods for predicting peak discharge of floodscaused by failure of natural and constructed earth dams. Water Resour. Res.,33(10):2337-2348.Wan, C.F., and R. Fell. 2004. Investigation of rate of erosion of soils in embankment dams. J.Geotech. Geoenviron. Eng., 130(4):373 -380.Xu, Y. and Zhang, L.M. 2009. Breaching Parameters for Earth and Rockfill Dams. Journal ofGeotechnical and Geoenvironmental Engineering, 135( 12): 1957-1970.Xu, Y. 2010. Analysis of Dam Failures and Diagnosis of Distresses for Dam Rehabilitation.Ph.D. Thesis. The Hong Kong U niversity of Science and Technology. January.PAGE 52"

...... rAppendicesJocassee DamValidation of HRRBreach Hydrograph forJocassee Dam

~,;aLp ~ ~ ;,Ipuuflp(;uu, -~ ~ ~ IPJ i...rri £.QUU(UJAppendix ABriaud's Report Appendix AJOCASSEE DAM17 January 2014Report to UJRSPrepared by: Professor Jean-louis BRIAUDI PhD., PE4Fig. 1 -Jocassee Dam1. MEETING LOGISTICSA meeting took place at the Jocassee Darn in South Carolina on 3 and 4 October 2013. Thepurpose of the meeting was to evaluate the erosion characteristics of the Jocassee Dam, whichforms a large storage reservoir 12 miles upstream of Duke Energy's Oconee Nuclear Power PlantComplex near Salem, South Carolina.The primary attendees were Dean Hubbard and Adam Johnson from Duke Energy; Chris Eyfrom HDR and Joe Ehasz from 2. MEETING PURPOSEThe primary purpose of the meeting and field trip was to become familiar with the Jocassee Damand materials and address the following questions:* Is your (Briaud) work applicable to embankment dam erosion?* What is your (Briaud) characterization of Jocassee dam erosion characteristics?PageA-I Appendix A* Please comment on Xu and Zhang work on dam breach, and how the three erodibilityclassifications, used by Xu & Zhang, compare to your six classifications.Important background details on soil erosion and rock erosion arc given in the Appendix.3. IS YOUR (B3RIAUD) WORK APPICABLE TO EMBANKMENT EROSION?The short answer is yes as long as the limitations listed below arc kept in mind; the work also hassignificant advantages also listed below. My work (B~riaud, 2008) is described in the backgroundsection of this report (Appendix). Of particular interest for Jocassee Dam are the charts shownbelow relating the critical velocity Ve to the mean grain size D50, the critical shear stress rc tothe mean grain size D50, the erosion rate dz/dt to the velocity V, and the erosion rate dz/dt to theshear stress r. These charts are repeated below for convenience (Fig. 31, 32, 33, 34). These chartswere developed on the basis of EFA testing (Appendix Section c, Fig. 5). This apparatusreproduces the erosion process at the element level where the water is flowing parallel to theinterface. Thle charts were developed from hundreds of EFA tests on vastly different soil typesover the last 20 years. The advantages and limitations of the applicability of these charts arelisted belowLimitationis:a. The soils tested over the last 20 years were soils that could be sampled in a 3 inchdiameter Shelby tube or re-compacted in a 3 inch Shelby tube to match the site condition.The largest grain size that was tested was about 7 mm diameter gravel. For soils particleslarger than that, the charts are based on published work by others including the US Arm)'Corps of Engineers for example.b. The Erosion Function Apparatus (EFA) reproduces a flow where the water is flowingparallel to the soil surface at the element level. Therefore using the EFA results for otherflow conditions should be done with caution and with engineering judgment.A dvan~tag~es:a. The work is characterizing the behavior of the soil at the element level so it is broadlyapplicable to many erosion situations, including soil and rockfill materials used inembankment dams. The measured function called the erosion function is to erosionstudies what the stress strain curve is to deformation problems. It is a constitutiveequation which can be used in numerical method as easily as in simple hand calculations.b. The wvork is very useful in the case of fine grained soils wvhere the erodibility is notrelated to the grain size.c. The work includes the critical velocity or critical shear stress for coarse grained soils androckfill based on an NCHRP project (Lagasse et al., 2006) which identified the USAGEequation as being the best among others. This equation is Eq. 8 in the Appendix forpredicting the required size given a velocity. The critical velocity charts for large rock fillblocks have this solid background and are applicable to soil materials and rockfills usedin embankment dams.d. The EFA tests which form the basis for these charts has been used to predict severalerosion processes in many materials. One example is the erosion that occurs in frneegrained and coarse grained soils around bridge supports as a function of time; Fig. 35Page A-2

&.....l. v3 L.uww .....J.,i.I -- Ilull V :U i..V.. ..rn.inl ms --v 3 n £urnA"p. .e.. ... A- shows the precision obtained in this case. Other examples of applications include leveeovertopping and meander migration in rivers.INTACI RIP-RAP&ROCK CLAY SILT [~~] ~ ~ ROCK.~ I100CRITICAI.VELOCITY. 10(m/s,) I0A10.01/ US ARMY CORPS OFFNGINEERS EM 1601eaVc=O" i(Dso)-02 V 45"t0.0001 0,001 0.01 0.1 1 1 0 I00 I000 10000MEAN GRINA SIZE. (ra) JOINT SPACING FORJOINTED ROCK* TMU 0mb ma vaoaebd Iy Iblaud. 4.4.. eta. 2be1, bada. PwNa. io A1l 0~ mb .pa.tab by bln*dk. 4.,4. (MU).m1o TodaS on -Nw Odlaain Lawnsa..*L dahd~ aumy, MWU., SLmit. WW ,wmetd yvnel .A.a. 17Fig. 31 -Critical velocity as a function of mean grain size (Briaud, 2013).__ ___ IUP-RAP &L~QROC~j CLAY SILT ~ GRAVEL JOINTED ROCKCRITICASI-WARSTRESS,(N/mn2)100000100I01001US ARMY CORPS OF11-0.0S~5(D)-4 BY SHIELDS (1936)I0010001 00O ! 001 1l 10I 100 1000 I0000MFEAN GRAIN SlEP Ds (rm JOINT SPACING FORJOINE ROCKe T~ltD Dab aa rapoanad by 5lel .1.4. 4.4..L (MIS). -iabdaeab .Ma OAslm~~ Law.Sa Dab Dar Sa Camay. UAS.Wlb, bmt WW a. rapa~bd by Vanaud. V.A..ad. (1gr5)..maulk~Matn Mae "da AWE aaNmmI.N. i N. oaa m pme.e, ABS.Maw Vail..Fig. 32 -Critical shear stress as a function of mean grain size (Briaud, 2013)Pge A-3 Inn i ii iIi iii in iii iiii 1m n iiii iiiii ... .... .... ....... .... .. ......-- vTtrw, IWm, Iv Appendix A1000-EROSIONRATE(mmr/hr)100-10-!-0.1/ High MedlInVery High Erodiblility Eod~ibliltyErodibility !1n /,di- m san /knc Rolnl"-N~-pan Slt-Fin Cirvel Erodiblbty-o.Platicity (2ih -Jomni Rock-All ssrd 3-0mmSangPlasncuy> Very LowInc-r-aIe in at-/s-Jointed Rock Vddol) rdbit(cla) / (I+0-I500 mm" Spacng)SP MLi ML H // -Euu"/-L % Rc ock VLw0.11.010I00VELOCITY (mis)Fig. 33 -Proposed erosion categories for soils and rocks based on velocity (Iriaud, 2013).100000I00001000-EROSIONRATE '00(mmn/hr)10-0.1Very High HighErodibility Erodibility / Medium-I Im + ErudIbIlt-o-pasclt* Sit -Lov, PzAsticsr, Silt LOW* , t~ 3r'm Erodlbil-Htpf Silt~ o-I. Phiaan~ity Clla / -l0- nu0 Sp ciq)--Cobbles-Increase a C~ctio / PlagiCti5SM (.,+. 'oiii 34Rc-increase ia WmeMLii CL iCH/ ->,IltyVery LowErodibiltyVNon-ErosiveV!0II0 100 10g0 10000 100000SHEAR STRESS (Pa)Fig. 34 -Proposed erosion categories for soils and rocks based on shear stress (Briaud,2013).Page A-4 Appendix A* Pier 3W[- o Pier 4E.3 -* Pier 5Eo0 Pier 23E*A Pier 24E< A Pier 25Ej v Pier 26E1 Pier 27EPier 28E________________ _Pier_29E0o1 2 3 4.MEASURED LOCA L SCOUR DEPTH (in)Fig.35 -Measured vs. predicted scour depth at Woodrow Wilson bridge (Briaud, 2008).4. CHARACTERIZE JOCASSE DAM.In order to evaluate the erosion function of the Jocassee Dam, the following process was used.a. A cross section of the darn was drawn (Fig. 36).b. An erosion category was chosen for each material wvithin the dam (Table 3); since thedrawings specified that the D5o was the minimum allowed, this selection is conservative.c. Three erosion levels were placed across the dam as shown on Fig. 36: level AA, BB, andCC.d. For each level, a weighted average of the erosion category was determined according tothe length of material exposed to the flow for that level.Z2:-1LiWhere EC is the average erosion category, Li is the length of material i exposed to water,and ECi is the erosion category for material i.e. Section AA gave an EC value of 3.93, section BB gave 4.08, and section CC gave 4.11.f. Therefore, the overall average erosion category for Jocassee dam is clearly 4 or lowerod ibi Iity.Page A-5 L.tJpj~rU55.~, ~ ~ I5iJtIIi.~U(JlI -VliILIIIIUIU....... jAppendix AFig. 36- Cross section of Jocassee Dam..Table 3 -Description of soil and rock materials in Jocassee Dam and erosion categoryMaterial(Fig. 36)Rock fillDescriptionEstimatedcritical velocity(mn/ErosionCategory:b)(7)(F)ImperviouscoreRandom fillFiltersA similar set of calculations were performed for the Teton dam. Fig. 37 shows the Teton Damcross section and the three levels selected for calculating the weighted average erosion categoryfor the Teton Dam. Table 4 shows the dam materials and their erosion categories. These erosioncategories were estimated based upon the material description in Seed and Duncan (1981). Thecalculations indicate that the weighted average of the erosion category according to the length ofmaterial exposed for that level are: Section AA gave an EC value of 2.5, section BB gave 2.63,and section CC gave 2.7. The average erosion category of Teton dam is therefore estimated to be2.6 or medium to high erodibility (Fig. 38).If the Teton Dam failure took 4 hours4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months for an erosion category of 2.6 (medium to higherodibility), and considering that the erosion categories are based on a log scale, it is clear that aJocassee Dam failure which has an erosion category of 4 (low erodibility) would take muchlonger.Page A-6

~.Uf1EWUfl5 ~U Univ .ZWFFUUVW UJUILiY UEIWI5LWI -WE5lwI~~a ,, wg. .....~,fl.. .AL........~ --- IC OfT? fl.iflOidiA.. .....i A -Mink WS E E334AA.c-SC~E30011 20011 1001 0*El 5232IA. 5132m --BlhFig. 37 -Cross section of Teton Dam.Table 3 -Description of soil and rock materials in Teton Dinm and erosion categoryJOMaterial (Fig. Description Estimated critical velocity Erosion37) ______________(m/s) CategoryZone I (Core) Silt with some clay, sand, and 0.2 2gravel ___________________Zone 2 Selected sand, gravel and 1 3.1!_____________ cobbles ___________________Zone 3 Miscellaneous fill 0.5? 2.5Zone 4 Selected silt, sand, gravel, and 0.8 3cobbles ___________________Zone 5 Rockfiil 2 4TETONDAMi10O0W Ver Hgh ig Medium J(OCASSEEErdbiiy Erodibilhty Ero~dtbilhty D)ANIp10000 Er-diblhity IIEROSION ,.S/.,... io RATE 100 -- .. ,,(mm/br) '" Very LowNI LI Rock\ 0.1(10.1 1.0 10 lOSVELOCITY (mis)Fig. 38 -Overall erosion category for Jocassee and Teton Dams (velocity based).PageA-7

.................................................................. m_.__...... r" .....A....... A~neoooo ~ tHIFEudIOOEROSIONRATE 100(mm/br)TETONflAM *-Uae.i(WASEE1gbIlbUily Medium I)AMII ErediblityIIIIAEVI I.~t. P1441b ~III .,,~d H,1.'.. PIs.'~.#' 4 U, '~ %f4fl~~* 'u" Very Low~ ~ U 4"" FrodIbIIity441~ nflNom-Erosi,Rock *Iq ~ VIIra fl*SP0.1/NILJ CC'0 1 10 100 100 I000 I000SHEAR STRESS (Pa)Figl. 39 -Overall erosion category for Jocassee and Teton Dams (shear stress based).S. COMMENT ON THE CHOICE OF ERODIBILITY OF XU AND ZHANG and HOWTHE ThREE ERODIBILITY CLASSIFICATIONS, USED BY XU & ZHANG,COMPARE TO YOUR SIX CLASSIFICATIONS?.The work done by Xu and Zhang is very useful as it is based on a database of observations. Sincethe authors point out that erodibility is the single most important factor, it is critical tounderstand how they defined the erodibility of the materials making up the dam. The threeerodibility classifications used by Xu & Zhang (2009) refer to low, medium, and high erodibility.From their publication, it appears that these three category designations correspond to the low(category 4), medium (category 3), and high (category 2) categories proposed by Briaud (2008).This was verified with the primary author (Yao Xu) durng his visit to Denver, CO in November2013. The categorization reflects the fact that the types of materials typically used for theconstruction of earth damns fall into the Briaud erosion categories 2, 3, and 4 with some category5 materials for rockfill dams. Indeed fine sands and non-plastic silts (Briaud category 1) andjointed and intact rock (Briaud category 6) are not used in eatdam engineering.6. CONCLUSIONS*The erosion function characterizes the behavior of the soil at the element level so it isbroadly applicable to many erosion situations including erosion of materials used inembankment dam construction. The erosion function is the curve which links the erosionrate to the water velocity or the hydraulic shear stress at the soil-water interface; it is toerosion studies what the stress strain curve is to deformation problems. It is a constitutivePage A-8 Append ix Aequation wvhich applies to the erosion mechanics of all materials including the materialsused in embankment dams and can be applied in numerical methods as easily as in simplehand calculations.* The erosion function starts at the critical velocity or critical shear stress for coarsegrained soils and rock fill. The rockfill values are based on an NCH-RP project whichidentified the USAGE equation as being the best among others. This equation is Eq. 8 inthe Appendix which gives the particle size corresponding to a giv'en critical velocity. Sothe basis of the critical velocity charts for large rock fill blocks has this solid backgroundand therefore applies to embankment dam materials.* The erodibility of the Jocassee Dam materials was evaluated; see Figures 38 & 39, andthe Jocassee cross-section materials are clearly and conservatively established to be "lowerodibility" materials.*The Xu and Zhang regression equations do showv and consider that erodibility is the mostsignificant factor in the development of embankment breach parameters. Thus, it is mostimportant, in evaluating their equations, to establish how Xu and Zhang have assignedthe "low, medium or high" erodibility to the various dams and data to establish theirregression equations. Use of the three classifications is appropriate since they dorepresent the characteristics of the most commonly used materials for construction ofembankment dams.7. OPTIONS FOR FURTHER STUDYThe following options for fuirther study can be pursued to refine the specific erodibilitycharacteristics of the dam materials, and the time necessary to erode Jocassee dam.a. Nuimerical simulations. The program CHEN 4D can be used to simulate the breach in 4dimensions (x, y, z, t) together with the erosion functions of the various materials. Thiswill give a much more precise time to total erosion than HEC-RAS which is a onedimensional solution of the problem. Professor Chen and I can team up for simulating thewater flow and the soil erosion. Such dam breach simulations are possible as shown onFig. 40 below. The results would be a movie with timed frames of the darn erosion as afunction of time with associated erosion versus time curves. Note that two distinct modesof failure need to be simulated: piping erosion followed by breach as the roof of the damembankment collapses (e.g.: Teton) and overtopping erosion and breach erosion startingat the bottom of the dam downstream face where the velocity is maximum (e.g.: HellHole). The first failure mode will be referred to as "'piping" wvhile the second one will bereferred to as "overtopping".b. Calibration based on previous failures (e.tg.: Teton and Hell Hole). The numericalsimulation must first be calibrated against the failure of known dams. CHEN 4D shouldPage A-9 fAppendix Abe used to duplicate the erosion process vs. time for the piping failures (e.g.: Teton Damn)and for the overtopping failures (e.g.: Hell Hole).c. Erosion function for selected dams. In order to directly measure the erodibility of thedam material, tube samples of the damn can be collected (e.g. Teton and Hell Hole) andrun in the EFA. This would require visits to the dam sites. Samples of the finer materialscan be taken by hand driving short thn wall steel tubes in the remaining part of the TetonDam. Rockfill from Hell Hole could also be collected and tested as explained next.d. Erosion function for Jocassee rockfill. In order to directly measure the critical velocityof the Jocassee Dam rockfili, flume tests can be carried out with rockfill material with aD50 matching the one from the dam. This can be done in a large laboratory flume atTexas A&M University where such a flume exists. Rockfill from the Hell Holereconstruction site could also be tested in that fashion.Fig. 44) -Example of advanced numerical modeling of interaction between water flowand a structure (Zhao, Chen, 2013).Page A-IO Appendix AREFE REN CES1. Briaud J.-L., 2008, "Case Histories in Soil and Rock Erosion: Woodrow Wilson Bridge,Brazos River Meander, Normandy Cliffs, and New Orleans Levees", The 9th Ralph B.Peck Lecture. Journal of Geotechnical and Geoe~n'ironmental Engineering. Vol 134.No. 10, ASCE, Reston Virginia,. USA.2. Briaud J.-L., 2013. "Geotechnical Engineering: Unsaturated and Saturated Soils". JohnWiley and Sons Publisher, 1000 pages.3. Lagasse P.F., Clopper P.E., Zevenbergen L.W., Ruffi.F., 2006, "Riprap Design Criteria,Recommended Specifications, and Quality Control", IVCHRP report 568. NationalCooperative Highway Research Program of the Transportation Research Board,Washington DC, USA, pp226.4. Seed, 1-LB., and Duncan, J.M., (1981), "The Teton Dam Failure -A RetrospectiveReview", Proceedings of l Oth International Conference on Soil Mechanics andFoundation Engineering, Stockholm, Vol. 4, pp. 2 19-238.5. Xu Y., Zhang L.M., 2009, "Breaching Paramneters for Earth and Rockfill Dams", Journal.of Geotechnical and Geoenvironrnental Engineering. Vol. 135, No. 12, ASCE, RestonVirginia, USA.6. Zhao Y., Chen H.-C., (2013), "CFD Simulation of Violent Free Surface Flows by aCoupled Level-set and Volume-of-Fluid Method", Proceeding's of the 2013 1SOPEConference. Anchorage, Alaska, USA.Page A-11 Appendix AAPPENDIXBACKGROUND ON EROSIONa. The erosion phenomenonAn erosion problem always has three components: the soil or rock, the water, and the geometryof the obstacle that the water is encountering. The resistance of the soil or rock is characterizedby its erodibility, the water action is quantified by its velocity, and the geometry of the obstacleby its dimensions. Fig. 3 shows a free body diagram of a soil particle, a cluster of particles, or arock block at the bottom of a lake. The water imposes ,a normal stress (hydrostatic pressure)around the soil particle or rock block. The normal stress is slightly higher at the bottom than atthe top since the bottom is slightly deeper in the water column. This normal stress differencecreates the buoyancy force which reduces the weight of the soil particle or rock block. Fig. 4shows the same particle, cluster of particles, or rock block at the bottom of a flowing river. Threethings happen when the water starts flowing. First, a drag force and associated shear stressesdevelop at the interface between the soil particle or rock block and the water flowing over it.Second, thde normal stress on top of the soil particle or rock block decreases because of the waterflow. Indeed, as the velocity increases around the particle or the obstacle, the pressure drops tomaintain conservation of energy according to Bernoulli's principle. This phenomenon is similarto the air flow on top of an airplane wing where the pressure is lower than below the wingthereby developing the uplift force necessary for the plane to fly. Third the normal stresses andshear stresses applied at the boundaries are fluctuating with time because of the turbulence in thewater. These fluctuations find their roots in the appearance and disappearance of eddies, vortices,ejections, and sweeps in the flowing water; they can contribute significantly to the erosionprocess especially at higher velocities. In some cases they are the main reason for erosion. Thecontribution of turbulence fluctuations to the erosion process has been studied by several authorsas reported by Briaud :2013. The combination of the mean value and the fluctuations around themean of the drag force and uplift force can become large enough to pluck and drag the soilparticle, soil particle cluster, or rock block away and generate erosion.Note that in the case of unsaturated soils or saturated soils with water tension, the mechanicalinter-particle compressive forces (fc1 in Fig. 3 and 4) can be significantly larger than in the casewhere the water is in compression. This apparent cohesion may increase the resistance to erosionat least until the flow and presence of water destroys the water tension.Page A-12

&1P.WL,41 ¶v r.:Wa2 ---rh i l~ j~1..... .. ...r-......... .. 9 tfl .jAppendixA--~ V2m Vymof.. -, ,me, etrtcal foce bee pa)rtic~le.1., -forces at co.~cts bewe psyticleeco = center of gravityW -weight of pertilel-wat, ver pri er aroun peii@.Fig. 3 -Free body diagram of soil particle or rock block for no flow (Briand, 2013)vx 4'v, +U-1t, -elctica forces bewe peruscleef -foce at coet between perficiesW -we4ight of u, -, wetr pressure around particle-shea~lr stes arond particle.Fig. 4 -Free body diagram of soil particle or rock block when water flows (Briaud, 2013)Page A-13 Appendix Ab. Erosion modelsThe erodibility of a soil or rock can be defined as the relationship between the erosion rate z andthe velocity of the water v near the soil-water interface. This definition is not very satisfactorybecause the velocity varies in direction and intensity in the flow field. In fact, strictly speaking,the water velocity is zero at the soil/rock-water interface. A more satisfactory definition is therelationship between the erosion rate z and the shear stress r at the soil/rock-water interface.ez = f(rt) (1)The erosion function described by Eq. 1 represents the constitutive law of the soil or rock forerosion problems much like a stress strain curve would represent the constitutive law of the soilor rock for a settlement problem. While a shear stresS based definition is an improved definitionover a velocity based definition, it is still not completely satisfactory as the shear stress is not theonly stress which contributes to the erosion rate. A more complete description of the erosionfunction is given by Eq. 2:____Ar ~(2)Where z is the erosion rate (mis), u the water velocity (m/s), "t the hydraulic shear stress, thethreshold or critical shear stress below which no erosion occurs, p the mass density of water(kg/in3), AT the turbulent fluctuation of the hydraulic shear stress, and Act the turbulentfluctuation of the net uplift normal stress. All other quantities are parameters characterizing thesoil being eroded. While this model is quite thorough, it is rather impractical at this time todetermine the 6 parameters needed in Eq. 2 on a site specific and routine basis. Today Eq. 3which corresponds to the first term of Eq. 2 is widely accepted.z-= (3)u t,,oU)As additional fundamental work is performed in erosion engineering, it is likely that Eq. 3 willevolve towards Eq. 2.c. Measuring the erosion functionAn apparatus was developed in the early 1990s to measure the erosion function. It is called theErosion Function Apparatus or EFA. The principle is to go to the site where erosion is beinginvestigated, collect, samples within the depth of concern, bring them back to the laboratory andtest them in the EFA. A 75 mm outside diameter sampling tube containing the sample is placedthrough the bottom of the conduit where water flowvs at a constant velocity (Fig. 5). The soil orrock is pushed out of the sampling tube only as fast as it is eroded by the water flowing over it.For each velocity, an erosion rate is measured and a shear stress is calculated using Moody's1944 chart (Briaud 2013). Point by point the erosion function is obtained.Page A-14 Appendix AWATER FLOWja(mm/hr)t(N/rn2)ISpOILPISTONPSHING ATRATE ZFig. 5 -Erosion Function Apparatus to measure erodibiity.Examples of erosion functions are shown in Fig. 6 for a fine sand and Fig. 7 for a low plasticityclay. Note that for the same average velocity of 1 m/s in the EFA test conduit, the rate of erosionfor the sand is about 1000 times faster than for the clay. This indicates that the rate of erosion canbe very different for different soils. Other devices have been developed to evaluate how resistantearth materials are to water flow. These include the rotating cylinder to measure the erosionproperties of stiff soils, the jet test to evaluate the erodibility of soils, and the hole erosion test tomeasure the erosion properties of stiff soils. More recently a simple and inexpensive tool forfield use has been developed called the pocket erodometer. It can be performed at the site on theend of a sample and gives a first indication of the erodibility of the soil within minutes aftersampling.10000*m 10)00.01 *0.11Veolcity (m/s)100001000100.0100S000101000.11 10Shear Stress (N/mn2)100Fig. 6 -Erosion function for a fine sand as measured in the EFA.Page A-15 L-,UfldiI.ll, *iaiIaIaIUIIQUI -VVILIIIIIJIU Iujlli pULUI1I Ul IJG iu Appendix A0O0lO.h" 00 0-0 "o 00.1 1 10 100 0..1 1 10 100Velocity (mis) Shear Stress (N/lm2)Fig. 7 -Erosion function for a low plasticity clay as measured in the EFA.d. Soil erosion categoriesCategories are used in many fields of" engineering: soil classification categories, hurricanestrength categories, earthquake magnitude categories. Such categories have the advantage ofquoting one number to represent a more complex condition. Erosion categories are proposed(Fig. 8) in order to bring erodibility down in complexity from an erosion rate vs. shear stressfunction to a category number. Such a classification system can be presented in terms of velocity(Fig. 8) or shear stress (Fig. 9). The categories proposed are based on 15 years of erosion testingexperience, in order to classify a soil or rock, the erosion function is plotted on the category chartand the erodibility category number for the material tested is the number for the zone in whichthe erosion function fits. Note that, as discussed later, using the water velocity is lessrepresentative and leads to more uncertainties than using the shear stress; indeed the velocity andthe shear stress are not linked by a constant. The velocity chart has the advantage that it is easierto gage a problem in terms of velocity.One of the most important soil parameters in erosion studies is the threshold of erosion. Belowthis threshold, erosion does not occur and above this threshold, erosion occurs. In terms of shearstress, this threshold is the critical shear stress rc and in terms of` velocity, it is the criticalvelocity vc. Fig. 11 shows a plot of the critical velocity as a function of the mean grain size whileFig. 12 shows the same plot for the critical shear stress. The data come from measurements in theEPA as well as measurements published in the literature. As can be seen on Fig. 1 1 and 12, therelationship between the critical value and the grain size has a V shape indicating that the mosterodible soils are fine sands with a mean grain size in the range of" 0.1 to 0.5 mam. This V shapealso points out that particle size controls the erosion threshold of coarse grained soils whileparticle size does not correlate with the erosion threshold of fine grained soils. Shields in 1936proposed a curve for coarse grain soils in his doctoral wvork which is included in Fig. 11 and 12.Shields recommendations do not include fine grain soils. Note also that Hjulstrom in 1935proposed such a curve for both coarse grain soils and fine grain soils but his recommendationsfor fine grain soils turned out to be too simple.Page A-16 Appndix A1e000EROSIONRATE 100-(mm/hr)10-0.1!0.1/ High MediumEludibility; II ~~/ -Meiu Sand Jot e-Fne Sand Low Pl~aiuot SilF i$pacmg: 30 // LOW/Nnpa~cSl Ffl o--Lo' .laau paiC/ Rck 'Very Low-ncrease/n COgjmCdibmty~SM -inces l /-JnnedRok(M -Inry7 n (~i mul Spacing)ML MH /PrHP/! CL CH Rock vI1w1.010100VELOCITY (mis)Fig. 8 -Proposed erosion categories for soils and rocks based on velocity.1O00000100001000EROSIONRATE 100o(mm/br)100.101 0 100 100 10000 100000SHEAR STRESS (Pa)Fig. 9 -Proposed erosion categories for soils and rocks based on shear stress.Page A-17 Appendi ACLAYSILSAN GRAVL JOINToED RocK1000100CRITICALVELOCITY, 10(rn/s.) I0.10.010.0001 0.001 0.01 0.1 1 1 0 100 1000 10000MEAN GRAIN SIZE, Dso (rm JOINT SPACING FORt- JOINTED ROCKmt P,..gtae.d ,A t.w*inem~. wl. A. Mew Vew.Fig. 11 -Critical velocity as a function of mesa grain size.PIN[TACT1RoC AY&SILTCR1IFICAI.SIIEARSTRESS, ;:(N/rn2)0.0001 0.001 0.01 0.1 1 10 100 1000 10000MEAN GRAIN SIZE, D~o (mam) JOINT SPACING FORJOINTED ROCK* T1M Game. ...by leudl .L,.L et R. (3,i.. "lk~m ,~e., A*pmuabsf M ew0r.m.A .0.eq.*. t. .171) eIFig. 12 -Critical shear stress as a function of mean grain sizePage A-i8 Appendix AThe erodibility of soils varies significantly from one soil to the next; therefore erodibilitydepends on the soil properties. It depends also on the properties of the water flowing over thesoil. For some soils, particularly dispersive soils, the higher the salt concentration in the water,the more erosion resistant a clay is. The properties influencing erodibility are numerous; some ofthem are listed in Table 1. It appears reasonable to expect that a relationship would exist betweencommon soil properties and erodibility. But erodibility is a function not a number thereforecorrelations can only be made with elements of that function such as the critical shear stress orthe initial slope of the erosion function. Such correlations have been attempted and failed withvery low coefficients of correlation. On one hand, there should be a correlation, on the otherhand, the correlation is complex and requires multiple parameters all involved in the resistanceof the soil to erosion. All in all it is preferable to measure the erosion function directly in anapparatus such as the EFA.Table 1 -Soil and water properties influencing erodibilitySoil clay mineralsSoil water content Soil dispersion ratioSoil unit weight Si ainecag aSoil plasticity index Soil catondexchaboping capSoil undrained shear str. Si oimasrto aSoil void rt-io Soil pHSoil swell Soil temperatureSoil mean grain size Water temperatureSoil percent passing #200 Water salinityWater pHe. Rock erosionIf soil erosion is not very well known, rock erosion is even less known and the engineer mustexercise a great deal of engineering judgment when it comes to rock erosion. Nevertheless manyengineers and researchers have contributed to the advancement of knowledge in this relativelynew field.Rock erodes through two main processes: rock substance erosion and rock mass erosion. Rocksubstance erosion refers to the erosion of the rock material itself while rock mass erosion refersto the removal of rock blocks from the jointed rock mass. Rock substance erosion includes threesub-mechanisms: erosion due to the hydraulic shear stress created by the water at the rock-waterinterface, erosion due to abrasion caused by sediments rubbing against the rock during the flow,and impact of air bubbles that pit the rock surface due to cavitation at very high velocities. Rockmass erosion includes two sub mechanisms: erosion due to slaking, and erosion due to blockremoval between joints. Slaking can occur when a rock, such as a high plasticity shale in anephemeral stream, dries out and cracks during summer months; these small blocks are thenremoved by the next big flood. Block removal can occur if, during high turbulence events, thedifference in pressure between the top and the bottom of a rock block becomes large enough toovercome the weight and side friction on the block. Brittle fracture and fatigue failure cancontribute breaking the rock into smaller pieces which then are carried away by the water. Notethat most of the time, rock mass erosion will be the dominant process in rock erosion with onlyPage A-19

-~Appendix Arare occurrences of rock substance erosion.The critical velocity associated with rock erosion is much higher than the critical velocityassociated with soil erosion in general. At the same time, the erosion rate for a given velocity ismuch lower for rock erosion than for soil erosion in general. Table 2 is an attempt at quantify hagthe critical velocity and the erosion rate of jointed rocks where the rock mass erosion maycontrol the process. This table is preliminary in nature and should be calibrated against fieldbehavior. The critical velocities quoted in Table 2 refer to the velocity necessary to move aparticle with a size equal to thle spacing between joints; as such they are likely lower boundssince they ignore any beneficial effect from the shear strength of the joints. Note that theorientation of the bedding of the rock mass is important as shown on Fig. 13. Engineeringjudgment must be used to increase or decrease the critical velocity when the bedding is favorableor unfavorable to the erosion resistance. in addition, it is highly recommended in all cases tomeasure the erosion function of the rock substance on core samples obtained from the site.Table 2 -Rock mass erosion; this table is preliminary in nature and should be calibratedagainst field behavior.Joint Critical.O ttSpacing Velocity Caerosy ofonnt(mm) (m/s) Caeoy oons<30 0.-1.35 Category Ill<30 0.-135 Medium"~ Not applicable30-150 1.35-3.5 Category IV Evaluation needed________ ___ ___ __ Low150 -1500 3.5-10 Category V Evaluation needed________Very Low>150 >10 Category VI>__1500_ >____ _ 10 Non-Erosive Not applicableFAVORABLE UNFAVORABLEORIENTATION ORIENTATIONFLO DRECTION FLO.W DIRECTION"Fig. 13 -Effect of joint orientation on erosion resistance.Examples of rock erosion rates can be collected from geology. For example, the Niagara Fallsstarted about 12000 years ago on the shores of Lake Erie and have eroded back primarily throughundercutting of the falls rock face to half way between Lake Erie and Lake Ontario. Thisrepresents 11I km and an average rate of 0.1 mm/hr, through sandstones, shales and l imestonessedimentary rocks. Another example' is the Grand Canyon where the Colorado River hasPage A-20

-Appendi Agenerated 1600 m of vertical erosion through complex rock layers over an estimated 10 millionyears for an average rate of 0.00002 mm/hr as the Colorado Plateau was up-heaving. These ratesappear negligible at first glance yet neglecting them would be neglecting the Grand Canyon orthe rera of Niagara Falls. The lesson is clear: it is not only the rate of erosion which isimportant but also the length of tine over which that rate is being applied.f. Water velocityFig. 1 4 shows the profile of water velocity as a function of flow depth. The water velocity islargest near the top of the water column and zero at the bottom. This has been measuredrepeatedly in hydraulic engineering. By comparison, the shear stress is highest at the bottom andnear zero at the top of the water column. The relationship between the shear stress and thevelocity can be established as follows. Because water is a Newtonian fluid, there is a linearrelationship between the shear stress 'r and the shear strain rate d'y/dt.C: -Y- (4)Where jt is the dynamic viscosity of the water (1 0. Pa.s at 200C). This viscosity is different fromthe kinematic viscosity v of water (10"+ m2/s at 200C) defined as v jj/p where p is the massdensity of water (1000 kg/in3). Since, as shown on Fig. 14, y is du/dz, then dy,/dt is dv/dz where vand u are the water velocity called shear velocity and horizontal displacement in the horizontaldirection at a depth z respectively. Then the shear stress r at depth z is given by:Therefore the shear stress is proportional to the gradient of the shear velocity profile with flowdepth and the shear stress at the soil/rock-water interface is the slope of the profile at theinterface. If the slope of the water velocity profile at the water-soil or water-rock interface(interface shear stress) is kept constant and if the water depth is varied, then it can be shown thatthe mean depth velocity will vary as well. This implies that there is no constant ratio betweenmean depth velocity and interface shear stress. This is one reason why velocity alone is not asgood a predictor of erosion as shear stress. As such, any erosion design tool presented in terms ofvelocity should be used with caution. On the other hand, velocity is much easier for the engineerto gage than shear stress, and this is why both velocity and shear stress are used in practice.Fig. 14 -Velocity and shear stress profile versus flow depthPage A-21 Appendix AThe magnitude of these shear stresses is very small and measured in N/rn2.They are muchsmaller than the shear stresses that the geotechnical engineer is used to calculate in foundationengineering for example which are in the range of kN/m'. Fig. 15 gives examples of the range ofshear stresses associated with various fields of engineering, If the undrained shear strength is areasonable measure of the strength of a clay for foundation engineering design, the critical shearstress is the "shear strength" of the same clay for erosion studies. The difference in magnitude ofthe stresses and the strengths for foundation engineering and erosion is that in erosion studiesone looks at the resistance of one particle, or a small cluster of particles, while in foundationengineering one looks at the resistance of the soil mass at the foundation scale.Vnnder Waals GuolochnicnlForceeo Shoat StronglhWeight of of SoillOne Soil Gralil Soft .-* V. Hord1 o = 01 ^WolLDepth 100 (in) 10-2Soil Shear Stress Involved(Himn2)Fig. 15 -Range of shear stresses encountered in different engineering fields.The water does not flow at a constant velocity in a river and the velocity history over a period oftime is a necessary input to many erosion problems. This velocity history or hydrograph is notusually readily available. Often, the discharge (ma/s) hydrograph is available and needs to betransformed into a velocity (mis) hydrograph and a water depth (in) hydrograph. This iscommonly done by using software such as HEC-RAS. An example of the results of thistransformation is shown in Fig. 16. HEC-RAS solves the one-dimensional energy equation forgradually varied flow in natural or constructed channels and adds the one-dimensionalmomentum equation around hydraulic structures such as bridges, culverts, and weirs where theenergy equation is no longer applicable.Page A-22 C7;:.:2=::_.2.:." " Z..:JL':. -:_ :;%..~..... ..... ~~ir... L Lu,m.. ,.;,. ..... c,- .....Appendix A-SQrQS.-012000100008000600040002000032iii Lihk.Ai&LAL~iLL4iLk196019701980TiME (yrs)199019981019601970 1980 1990TIME (yrs)1998TIME (yrs)Fig. 16 -Discharge, velocity, and water depth hydrographsThe hydrograph can be used to obtain the 100 year flood or the 500 year flood. One simplegraphical method consists of obtaining the yearly maximum flows from the hydrograph, rankingthenm in descending order of intensity, calculating for each flow the probability of exceedance asthe rank divided by the total number of observations + 1, then plotting the flow versus theprobability of exceedance on a semi-log paper such as the one of Fig. 17. Once the data isplotted, a linear regression is performed over say the first 20 to 30 years of data and extrapolatedto the 0.01 probability of exceedance for the 100 year flood and to the 0.002 probability ofexceedance for the 500 year flood. Indeed the return period is the inverse of the probability ofexceedanice. There are other and more refined ways of obtaining these design floods but thissimple graphical method helps understand the process and the meaning of the 100 year flood: aflood which has a 1% chance of being exceeded in any one year. Fig. 17 shows the result of ananalysis for the hydrograph at the Woodrow Wilson bridge. As can be seen on that figure, the100 year flood has a discharge of 12,600 m3/s and thc 500 year flood has a value of 16,600 m3/s.Page A-23

~2~taI~ :-ft- ~-~sm~r, !~srrnsW..-~ 1~rhs5d n-su ~~u; v:;r..~. -10 cm LNO:iAppendix AFLOOD-FREQUENCY CURVE BASED ONORIGINAL HYDROGRAPH (1931-1999)y -2491O6y(xr262 lod 12629n9/s:++t?p ! + SO...... ? p+-+:-+y+-,ca +?... -++ ..lo.. 16639m. .+3s .(m J/s)01001010.1PERCENT PROBABILITY OF EXCEEDANCE IN ANY ONEYEAR (%)Fig. 17 -Flood frequency curve obtained from measured discharge hydrograph.The probability of exceedance R of the design flood with a given return period T1 depends on thedesign life l~ of a structure.am 1 _(1 l /Tr)Ut (6)if the design life of the bridge is 75 years, the probability that the flood with a return period of100 year will be exceeded during the 75 year design life is 53% according to Eq. 6 and thatprobability is 14% for the 500 year flood. Only when one gets to the 10,000 year flood does theprobability get to be lower than 1% (0.75%). Therefore looking at those numbers alone, it seemsdesirable to use the 10,000 year flood for design purposes. This flood is used in design in theNetherlands for regions of the country deemed critical. The USA uses the 100 and 500 year floodfor design purposes in hydraulic engineering; this leads to probabilities of exceedance which arein the tens of percent. By comparison, the structural engineers use a probability of exceedance ofabout 0.1% for the design of bridge beams (LRFD target) and, judging from measured vs.predicted pile capacity data bases the geotechnical engineer uses a probability of exceedance ofthe order of a few percent. While these numbers can be debated, it is relatively clear that thesedifferent fields of civil engineering operate at vastly different probability of exceedance levels.Note that risk is different from the probability of exceedance as it also involves the value of theconsequence. As such, the probability of exceedance target should vary with the consequence ofthe failure.g. Geometry of the obstacleThe geometry of the obstacle encountered by the water influences the velocity of the water andthe flow pattern including turbulence intensity. When the water approaches a pier in a river forexample it has to go around the pier. In doing so it faces a restricted area and has to accelerate tomaintain the flow rate. This acceleration results in a local mean depth velocity which can be 1.5Page A-24 Appendix Atimes higher than the approach mean depth velocity. If the approach velocity is lower than thecritical velocity but the local velocity around the pier reaches a value higher than the criticalvelocity, then scour occurs around the pier. This scour type is called clear water scour that is tosay scour created by water which does not carry soil particles. On the other hand, if the approachvelocity and the velocity around the pier are both higher than critical, then the scour type is livebed scour. This means that the water is carrying a significant amount of soil particles. The scourdepth reached under live bed scour conditions is typically less than the scour depth reachedunder clear water scour conditions. The reason is that during live bed scour some of the particlesin suspension fall down on the river bed thereby limiting the depth of the scour hole around thepier.Fig. 18 a and b show results of numerical simulations of erosion createdcontracted channel. The CHEN 4D computer program is the program used.by water flow in a(a) Scour depth and shear stress distributions at t -2000 minshear stress distributions at t -15000 minFig. 18 -Predicted scour hole shape and streambed shear stresses around abutments andpiers: (a) t =2000 rain, (b) t =15000 win (From Chen, 2002)Page A-25 Appendix AIi. Background on levee overtoppingThis background is given here because it is related to the topic of dam erosion. Levees are smallhomogeneous damns which only retain water fr'om time to time as opposed to damns which aretypically larger and retain water all the time. Nevertheless, this previous wvork carries someresemblance. Levees or dikes are small dams build along a river or.an ocean to prevent the waterfrom inundating the land in case of flood. The top of the levee is set at a predetermined heightcorresponding to the water level for a chosen design flood. This flood corresponds to a certain*return period such as a 100 year flood. If the flood exceeds the design return period, water islikely to flow over the levee and generate potential erosion. One of the first observations is that ifthe water flowvs above a levee of height IH, by the time the water reaches the bottom of the dryside of the levee it will have a velocity V which can be very high. One simple way to evaluatethat velocity is to write conservation of energy.mgH =lmrv2 or V=/-H(7)2For example if the levee is 5 m high, the velocity v will be approximately 10 m/s. Of course Eq,7 does not take into account the energy lost in friction between the water and the levee surfacebut it does indicate that the velocity range is much higher than typically encountered in riverswhere the wvater flows at most in the range o~f 3 to 4 m/s. Furthermore a distinction should bemade between events such as hurricanes on one hand and river floods on the other. The majordistinction is that hurricanes may overtop a levee for about 2 hours2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months while river floods mayovertop a levee for 2 days. A levee overtopping erosion chart has been developed for these twotypes of events and is presented in Fig. 19. It indicates which soil categories and associatederosion ffunctions are likely to resist overtopping during a 2 hour2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months and a 2 day overtopping. Recallthat categories I to IV on the erosion chart are soils and categories V and VI are rocks. As can beseen, only the most erosion resistant soils can resists 2 hrs of overtopping without protection(Category IV) and no soil can sustain 2 days of overtopping without being totally eroded away.Armoring or vegetation satisfying strict criterions need to be used to ensure that overtopping canbe sustained for longer than 2 hrs.Vegetation can help significantly to retard erosion. This vegetation however has to satisfy thefollowing minimum requirements. It should have a mat-like appearance, a sod-forming rootsystem, be made of perennial grasses, have a dense consistent coverage, have a minimum heightof 0.3 m during flood season. Tree roots can be considered to help reinforce the levee slope if thetree is on the levee however if the tree is toppled over by the storm, it will create a major hole inthe levee. Also if the tree dies, the disappearance of the roots will leave channel for the water toseep through the levee. Overall trees on levees or near levees are not a good idea.The followving case history illustrates how the levee overtopping chart was generated.Page A-26 i4... CsA~~~~~. ~ w -L....k.. Sw1. .il.w1 C LwIJAppendix A10000 A~ty/ Meodibiit10000 l E tRAT 1000 alr y(mm/hr) Very LowFailre 2hrsErodibilityNon-Erosive0.1 0.1 1.0 10.0 100.0VELOCITY (rn/a)Fig. 19 -Levee overtopping chart.i. New Orleans -Katrina hurricane levee case historyOn August 29. 2005, levee overtopping and associated erosion contributed significantly to theKatrina hurricane disaster in New Orleans where some places are 6 m below the top of thelevees. This case history describes the process by which overtopped levees e-rode and whether ornot unprotected soils can resist overtopping erosion.Soil erodibilit"Thin wall steel tube samples and bag samples were obtained from the top of the levees at shallowdepth (0 to I in). Shelby tube samples and bag samples were collected from locations S1 through515 on Fig. 20. The bag samples were reconstituted in a Shelby tube by recompacting the soil ata low and at a high compaction effort. The soil type varied widely from loose uniform fine sandto high plasticity stiff clay. EFA tests were performed on the samples. The results of all the testsarc shown on Fig. 21 and 22. One of the first observations from those figures is that theerodibility of the soils obtained from the New Orleans levee varies widely' all the way' from veryhigh erodibility (Category I) to low erodibility (Category 4). This explains in part why some ofthe overtopped levees failed while other overtopped levees did not.Page A-27 U----- -U--.Appendix AFig. 20 -Location of shallow samples collected from the top of the levees.im000Very High HighErodIb~y

Medium0li!000 ° a Low* I ErodtbilityEROSION iRATE 100 *

1(mm/br) l,

a10

a VrylowI *NonErodlb 0.1 -"'I- " 0.11.0 10.0VELOCITY (m/s)100.0Fig. 21 -EFA test results in terms of velocity for some levee soils.Page A-28 Wu.Wl,, t3W.U,;#1, .JWV..U, uu,,,'ww,W -u,.,,,.ug .fl,. WE.f3rW per iu I/d- LJIu(G)Appendix Aia-e / I EfOGDU/I III,- ~ ~~~.' ': // ,,(miniar)IklI0 I i0 ioo 1see tWooo lIooSHEAR STRESS (Pa)Fig. 22 -EFA test results in terms of shear stress for some levee soils.Water velocityHurricanes are large rotating ma~sses of moisture which can be 400 km in diameter. They travelrelatively slowly at speeds of about 40 kmn/hr. Therefore a hurricane takes about 10 hr to go overa levee or a bridge. The worst part of the storm however is only a fraction of that time. Thefriction generated by the wind at the air-water interface drags the water into a storm surge whichcan reach several meters above the mean sea level and kilometers in length. The surge associatedwith Katrina was about 8.5 m at Bay St. Louis, 4.6 m at Lake Borgne, and 3 m at LakePontchartrain. The storm surge was high enough to overtop some of the levees. As discussedearlier the water velocity at the bottom of such levees can reach 10 mis.Geometry of the obstacleMost levees around New Orleans are between 3 and 6 m high. They have two main shapes. Thefirst one consists of a flat top which is some 4 m wide with side slopes at about 5 horizontal to !vertical. Because the width of such a levee configuration takes a lot of space, the second shapeconsists of the same shape as the first one at a reduce scale with a vertical wall extending on topof the levee. The problem addressed here is limited to the first shape (no wall).Predictingj levee overtopping erosionThere was overwhelming evidence that the water overtopped the levees in many places; suchevidence consisted mostly of ships being trapped on top of the levees when the water receded butalso of debris stuck in trees at levels higher than the top of the levees. Some levees resisted theovertopping well, some levees were completely eroded. On Fig. 23, the erodibility functions forthe samples taken from levees that were overtopped and resisted well are plotted as open circleswhile the solid dots are for the samples of levees that were completely eroded. As can be seen.the eroded levees were made of soils in the erodibility categories I and 2 while the levees whichresisted well were made of soils in the erodibility categories 3 and 4. This led to the leveeovertopping chart shown in Fig. 19.Page A-29 Appendix Ao ub Er *e IIIIN""* IVRAmTE' tO Vety Low.I * -,,0.1 10I. OkYELOITY (mnls)I LFig. 23 -EFA test results for the soils of levees which failed and did not fail by overtoppingerosion.j. Countermeasures for erosion protectionCountermeasures for erosion protection include a number of solutions but the most prevalent isthe use of rip rap (Fig. 24). Rip rap can be sized by the following USACE equation.Where d3o is the particle size of the riprap grain size distribution curve corresponding to 30%finer, Hw is the water depth, F is the factor of safety, C1, is the stability coefficient, C. is thevelocity distribution coefficient, CG is the blanket thickness coefficient, Vde iS the mean depthwater velocity, Cs, the side slope correction factor, G, the specific gravity of the riprap, and g theacceleration due to gravity (9.81 m/s2). The stability coefficient C11 takes into account theroughness of the riprap blocks; it is 0.3 for angular rock and 0.375 for round rocks. The velocitydistribution coefficient C+ takes into account the fact that water tends to accelerate on the outsideof river bends; it is I for straight channels and inside of bends, and 1.23 in most other cases. Theblanket thickness coefficient C6 is a function of the riprap gradation with a default value of I inthe absence of additional data. Thne velocity Vde is the mea depth velocity for straight channels.For river bends it is given by:Vk, (1.74- 0.52 (9)where Vac is the mean depth velocity upstream of the bend, Rc is the centerline radius ofcurvature of the river bend and W the river width at the water level. The side slope coefficient C5,is given by.PageA-30 Am AAppendx A= ~i(~~) (10)where 0 is the bank angle in degrees. The specific gravity of solids G, is usually taken as 2.65.It is very important to place a filter between the soil to be protected and the riprap layer. Withouta filter the soil under the riprap may continue to erode through the large voids in the riprap. Inthe end the riprap may not move away but may simply go down significantly as the underlyingsoil erodes away. The filter may be a sand filter or a geosynthetic filter.DESIGN PLAN __ FIELD INSTALLATIONFig. 24 -Riprap with geosynthetic filter InstallationOther countermeasures to prevent erosion include:1. Flow deflectors such as spurs, jetties, dikes, guide banks,2. Rigid armoring of the soil surface such as soil cement mixing and grouted mattresses,3. Flexible armoring such as riprap, gabions, articulated blocks,4. Pier geometry modification such as slender pier shape, debris deflectors,S. Vegetation such as woody mats, root wads,6. Fixed and portable instrumentation such as sonars, float out devices, and7. Periodic inspection.k,. Internal erosion of earth damsIt is estimated that 46% of earth dam failures occur due to internal erosion (Fig. 25) and half ofthose failures occur during the first filling of the reservoir. Yet, internal erosion of earth damsremains highly based on engineering judgment and experience. While guidelines andpublications exist much remains to be studied and researched in this field. For internal erosion ofan earth dam to take place, the following are required1. a seepage flow path and a source of water2. erodible material that can be carried by the seepage flow within the flow path3. an unprotected exit, from which the eroded material may escape4. for a pipe to form, the material must be able to form and support the roof of the pipe.Four different phenomena can lead to internal erosion of an earth dam (Fig. 26):PageA-3I Appendlix AI. backward erosion2. concentrated leak3. suffusion4. soil contact erosionBackward erosion is initiated at the exit point of the seepage path when the hydraulic gradient istoo high and the erosion is gradually progressing backward forming a pipe. A cocnrtdlais internal to the soil mass, it initiates a crack or a soft zone emanating from the source of waterand may or may not progress to an exit point. Erosion gradually continues and can create a pipeor a sink hole. Sufso develops when the fine particles of the soil wash out or erode throughthe voids formed by the coarser particles. This occurs when the amount of fine particles issmaller than the void space between the coarse particles. If on the contrary, the soil has a wellgraded particle size distribution with sufficiently small voids, suffusion is unlikely. Soils arecalled internally unstable if suffusion takes place and internally stable if particles are not erodingunder seepage flow. Soil contact erosion refers to sheet flow at interfaces between soil types. Itmay occur for example when water seeps down the back face of the core at the interface with thefilter and then the stabilizing mass.Earth dams deform during and after construction. This movement can be compression, extensionand shear distortion. Because typical dams are made of different zones playing different rolesthey exhibit different deformation characteristics. This can lead to differential movementresulting in cracks or soft zones where internal erosion can be initiated. Shrinkage can also createcracks which are prone to erosion if water comes to flow through them. Fell and Fry summarizedthe most likely locations where internal erosion can start in an earth dam (Fig. 27).TETON DAMFig. 25 -Eiample of internal erosion of an earth damn.Page A-32 Contains Security Sensitive Information -Withhold from public disclosure per 10 CFR 2,390(d)Appendix ACONTACT EROSIONSCONCENTRATED\ ,LEAK-BACKWARDEROSIONFig. 26- Mechanisms of internal erosion failures.DAM AXISSSPILLWVAYRIGHITABUTMENTSECTION IBEDOWNSTREAM-~ -5wFOUNDATiON ~ ~I. Spillway wall interface2. Adjacent to condnit3. Crack associated with steepabutment profile4. Desiccation on top of core5. Embankment to foundation6. Foundation ( if the foundation is soil orerodible rock)7. Embankment through poorly compacted layer,crack, (or by backward erosion if the core iscohesioniess)Fig. 27 -PosSible locations of initiation of internal erosion (After Fell, Fry, 2005).Page.A-33

..,ph, pI;,l,5i. -d; ..,Vs H '..rT' 5..F~ LI(UJAppendix ACoarse silt and fine sand are among the most erodible soils. Therefore earth dams containingsignificant amounts of such materials will be more prone to internal erosion. Clays in general andhigh plasticity clays in particular are more resistant to erosion as long as the electrical bondsbetween particles are not destroyed by chemicals. It seems that some core materials of glacialorigin such as glacial tills can be particularly susceptible to internal erosion. Sherard gave arange of gradation of soils which can lead to internal erosion problems (Fig. 28).The soils which are most susceptible to suffusion are those where the volume of fines is less thanthe volume of the voids between coarse particles. In this case, the fines can move easily betweenthe coarse particles and erode away to an exit face. After suffusion, such soils are devoid of finesand become very pervious clean gravel for example. Fell and Fry again indicate that gap gradedsoils and coarsely graded soils with a flat tail of fines (Fig. 29) are most susceptible to suffusion.10080PERCENT 60FINER(%) 40200 ~0.0010.01 0.1 1 10GRAIN SIZE, mm100 1000Fig. 28 -Range of problems soils for internal erosion (after Sherard, 1979).1008060PERCENTPASSING40200 '-0.13000.01 0.2 I 1oPARTICLE SIZE (ram)! 00 !1000Fig. 29 -Range of problems soils for suffusion (after Fell and Fry, 2005).Page A-34 Appendix AOne of the important criterions to evaluate erosion is to calculate the hydraulic gradient andcompare it to the critical gradient. The critical gradient is given byValues of icr typically vary in the range of 0.85 to I .2. The hydraulic gradient in dams dependson many factors including the difference in water level between the upstream and thedowvnstream, the length of the drainage path, and the relative hydraulic conductivity, of thevarious zones. The target maximum gradient in the flow must be kept much lower than thecritical value especially in areas where internal erosion is possible. Fig. 30 shows ranges ofhydraulic gradient values which are associated with initiation of internal erosion on one hand andfull development of piping on the other for unfiltered exit faces. Generally speaking there is atrend towards higher porosity soils beginning to erode at lower hydraulic gradients even lowerthan 0.3. Yet soils wvith plastic fines erode at higher gradients but gap-graded soils begin to erodeat lower gradients than non gap-graded soils with the same fine content. The US Army Corps ofEngineers uses a lowver bound value of the critical hydraulic gradient equal to 0.8 and allows ahydraulic gradient of up to 0.5 at the toe of levees provided a number of conditions are met(USAGE). Another way to address the incipient motion of soil particles in internal erosionproblems is to use the concept of critical velocity and charts such as Fig. II1 and 12. Howveverthese critical velocities were developed from sheet flow test and the critical velocity may bedifferent from those initiating internal erosion.1.2 __.._, iE 1.0 *L "'" P~ *'" *." "0.8/"":" 9HYDRAULIC V .. ..**GRADIENT 0.6 ** .~0.2 .:: 1 2 3 4 5 6COEF. OF UNIFORMIT"YCuI D6/DIOFig. 30 -Range of hydraulic gradient values associated with internal erosion (afterPerzlmaier, 2005).Most of the time, a complete breach occurs within 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months Of first visual detection of internalerosion and sometimes in less than 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months . The majority of failures occur during the first fillingor within 5 years after first filling. The process of suffusion tends to develop more slowly thanthe back erosion and piping process.Page A-35 Appendix AThe solution to many of the internal erosion problems is the use of quality filters. A filter is alayer of soil placed between a fine grained soil and coarse grain soil to transition the flowwithout having the fines of the fine grained soil erode through the voids of the coarse grainedsoil. The grain size distribution curve of the soil filter layer is designed to provide this transitionin a gradual fine to coarse fashion.Page A-36 Appendix BOriginal Xu and ZhangRegression Equationsand HRR Hydrograph a..

I,;I,,.,cIII U ,U -" .... " ua ..... -i i,~a~iw i,~ n £.W~dAPPENDIX BAPPENDIX B. ORIGINAL XU AND ZHANG REGRESSION EQUATIONSB.1 OverviewThe original Xu and Zhang (2009) regression methodology and its previous implementation tothe Jocassee Dam are described in this Appendix. This provides background for Section 6where we address the questions raised by the* FERC and the NRC. It also provides backgroundfor Section 7 where we describe the implementation of a revised version of the Xu and Zhangequations in a sensitivity analysis, which provides support for the breach hydrograph submittedin the Hydrologic Reevaluation Report (HRR) to the NRC by Duke on March 12, 2013 (Duke2013).Section B.2 summarizes the breach parameters and control variables in the Xu and Zhang(2009) regression equations. Section B,3 discusses the case histories that were used todevelop these equations and Section B.4 summarizes the regression equations, including theirconfidence limits. The implementation of the original Xu and Zhang (2009) methodology for theJocassee Dam is described in Section 8.5 and details of the use of the failure time estimate inthe HEC-RAS model are discussed in S ection B.6,B.2 Breach Parameters and Control VariablesThe Xu and Zhang (2009) multiple regression equations were developed to pred'ict the followingfive breach parameters (dependent variables), which are divided into two groups, breachgeometry and breach hydrograph:* Breach Geometryo Breach depth (Hb)o Breach top width (Bt)o Average breach width (Boe)* Hydrographo Peak outflow rate (Qp,)o Breach development time or failure time (T1)The predicted breach side slope, z, which is an input to HEC-RAS breach model, can becalculated from the breach depth (Hb), breach top width (Bt) and average breach width (Bave).The predicted breach bottom elevation, which is also an input to the HEC-RAS breach model,can be calculated by subtracting the breach depth from. the d/am crest elevation.Unlike most previous breach parameters regression relationships, Xu and zhang (2009)included :soil erodibility as a' control (independent) variable. In fact they found it to be the singlemost important of all the control Variables that they considered in terms of its explanation of thevariance in "observed" breach parameter values across the case histories ,on which theirmethodology is based.P AG6E B-I

.., -"rI-nr,,iu; [u,,,aw puunvu uiacl.iuure per 1u 1PMK x.JWu(a)APPENDIX BThe complete list of five control variables that they used to estimate breach parameters is asfollows, including norm atization for the first two variables:* Dam height (X1 = -dH,.r, dam height Hd and areference height Hr, where H,.= 15mi),* Reservoir shape coefficient ('X2 11/Hw, volume of water above breach invert Vw anddepth of water above the breach invert at the time of failure, l-w.),* Dam type (with corewalls, concrete faced and homogeneous/zoned-fill),* Failure mode (overtopping and seepage erosion/piping),* Dam erodibility (high, medium and low).Xu and Zhang (2009) included rock-flll dams in :the homogeneous/zoned-fill dam type. Damtype, failure mode and dam erodibility are included in the regression analysis as virtual discretevariables that represent either the presence or absence of each of these attributes.As mentioned above, Xu and Zhang (2009) found dam erodibility to be the most importantcontrol variable for predicting all five breach parameters. They describe dam erodibility as arelative measure based on the embankment material compositions and compaction conditions,dam cross-sectional geometry, construction time and other relevant pieces of constructioninformation. The three erosion categories (low, medium or 'high) used in the Xu and Zhang(2009) equations refer to the technical lecture paper by Briaud (2008), whereby soils and rocksare classified into various erosion resistance categories based on erosion velocity or shearstress, as shown in Figures 4.1a and b, respectively. The appropriateness of using the Briauderosion categories in the Xu and Zhang (2009) methodology was confirmed by Professor Briaudas detailed in Appendix A and summarized in Section 4.2.B.3 Case HistoriesThe Xu and Zhang (2009) regression equations are based on an analysis that includes morerecent breaches than are included in earlier relationships, such as Froehlich (1 995a and b). It.also includes data from China that has not been previously used in breach regressionequations. Data from a total of 75 earth and rockflll dam failure cases was used to develop theoriginal multiple regression equations, although for each breach parameter the number of casehistories that were used to estimate the best exact and best simplified equations, respectivelyare as listed below:* Breach depth (Hb): 66 and 71* Breach top width (Bt): 54 and 61* Average breach width (Bay.): 45 and 53* Peak outflow rate (Qp): 34 and 39* Breach development time or failure time (Tt): 28 and 30PAGE B3-2 I------ 5~~* -- -- -------I-,...... .....APPENDIX B38 (51%) of the 75 case histories are for US dams, 32 (43%) are from China and 5 (7%) arefrom other countries. 7% (5) of the 75 case histories are for dams that were classified as damswith core walls, 5% (4) were classified as concrete-faced dams and the remainder wereclassified as composite-fill dams. 61% (46) of the case history dams failed by overtopping and39% (29) by seepage-erosion failure modes. 40% (30) of the case history dams were classifiedas high erodibility, 51% (38) as medium erodibility and 9% (7) as low erodibility.Figures B~la and b show the depth of water abOve breach invert, Hw, and volume of water atthe breach time, Vw, for the 75 case histories onarithmetic-arithmetic and arithmetic-logarithmicaxes, respectively. Across the 75 case histories the depth of water above breach invert, Hw,ranges from 1.7 to 77 m (5.5 -254 feet) compared with a predicted value of 72.5 m (238 feet)for the Jocassee Dam using the original Xu and Zhang (2009) methodology. The dam heights,Hd, range between 3.2 and 93 m (10 -305 feet) compared with 117.3 m (385 feet) for theJocassee Dam. The volume of wafer at the breach time varied between 0.025 to 660.0 m3 x106 (5.5 -535,000 acre-feet) compared with a predicted value of 1.34 x 108 m3 (1,088,208 acre-feet) for the Jocassee Dam using the original Xu and Zhang (2009) methodology.B.4 Regression Equations and Confidence IntervalsXu and Zhang (2009) developed two types Of multiple regression eqUatiOns for estimating thefive breach parameters:* Best exact prediction equations -based only on failure cases where all five controlvariables were available, Best simplified prediction equations -includes some additional failure cases where notall five control variables were 'avail ableBest exact prediction regression equation for breach depth is in the following additive (linear)form:Yj= bo + blX1.+ b2X2 + (b31X31 + b32X32 + 3) + (b41X4 + b42X42)'+ (bslX51 + b52X52 + bs3X53) (1)in which:= the first (i.e. i = 1) breach parameter or dependent variable, i.e.normalized breach depth as defined in Figure B.2Xii = the control variables as defined in Figure B.2bjj = the regression coefficients corresponding to the control variablesPAGE B-3 cz-vzt.: Uu,.~tf.,.. L:.........L~.... ~1~4~rr-- -E'~af -- 10 017? E.W~1................. 0APPENDIX BOriginal Xii and Zhang DataU70I.150'40.ISOthermIOCahOO O~iin.I Xu and IU0 200 400 6OCX 8O0 1000 1200V.Iqmwe of wowr awe bq,.d hwmt Vw Ii. 106 m311400a) Arithmetic-arfthmetlc scalesOriginal Xii and Zhang Data80tIU140I9U.1D;X.* oU* USAm Chin amJoca.., -o~rigin xu rand Zhang10000.01 0.1 1 10 100Vuiwn. of wotr do,. beumds Inwt Vw Ia 106 m33b) Arithme.timogarlthmic scalesFigure B.1. Depth of water above breach invert vs. volume of watr at the breach time forthe original Xu and Zhang (2009) case h Istborles.P A E B3f -4

'~t~"~ ~~tf1tr b'Orre!r S nT3J~i1Jta3fl w;u~j: r:.... ,....LL... ~ ,.,~. ~,.APPENDIX BBreaching Parameters Control VariablesBreach .depth Yt= Jib/Ha Dam height X =H/rBreach top width Y= Bt/Hb Reservoir shape coefficient x2 = w ,,Average breach width Y3 = Bave/Jib Dam type X31 X32 X33Peak outflow rate y, O/ 13 with corewalls la(eb) 0(1) 0(1)Failure time Ys= T1,/T,. concrete faced 0(1) 1(e) homogeneOus/zoned ,fill 0(1). 0(1) 1(e)Failure mode X42 X42,overtopping 1(e) 0(1)seepage erosion/piping 0(1) 1(e)Dam erodibility xs2 X52 xs3high ,l(e). 0(1) 0(1)medium 0(1) 1(e) 0(1)low 0(1) 0(1) 1(e)Note: B Values for additive regression analy sisb Values for multiplicative regression analysis.Hr=15m; T = 1hourFigure B.2. Summary of the five breach parameters and five control variables in the Xuand Zhang (2009) regression-eq uationsFor the other four breach parameters, the following multiplicative (non-linear) form of regressionequation was Used in which all five .control variables were included for the best exact predictionequations but a subset of these variables were included for the best simplified predictionequations, as described below:. --= z (3)in which:Yj = the second through fifth (i.e. ! = 2, 3, 4 and 5) breach parametersor dependent variables as defined in Figure B.2Zt = untransformed breach parameter in natural space,To obtain the predicted breach parameter values in natural space a log transformation must beapplied to from Equation 2 , as follows;Zi = log (Y 1)= b0, + b1X1 + b2X2 + (b31X31 + .b32X32 + 3) + (b41X41 +I-b42X42) +(b51X61+ b52X52+ b83X53) (4)P AG EB-S

,[,.a -II,..,IU ,.u,, puI, Up PUt Iv .,rI ~APPENDIX BUnder the standard assumption in regression analysis that the variability, in the breach*parameters that is not accounted for in (i.e. explained by) the regression equations (i.e. by the*variation in the values of the control variables) is distributed according to a normal or Gaussian(bell curve),.probability distribution (Haan 1977). Under this assumption, the mean valuespredicted that are obtained using Equations I and 2 are also the median or 5-0th percentilevalues. However, for the multiplicative form of the reg~ression equation in Equation 2, the. effectof the log transformation shown in Equation 4 is that the variability in the breach parameters thatis not accounted for in (i~e. explained by) the regression equation is distributed according to alog-normal probability distribution. After 'transformation, the mean value., predicted intransformed log space from Equation 2, which is also the median or 50th percentile value in logSpace, is still the median ,in the natural space but it is not the mean value in the. natural spacedue to the effect of the log transformation. Another effect of this log transformation is that theconfidence intervals .are asymmetric.By design, all five control variables appear in the best exact prediction equations as shown in'Figure B.2. However, for breach depth, Hb, the best exact prediction equation excludes thereservoir shape coefficient (X2 = VW, '3!Hw) for two reasons. First, the reservoir shape coefficientwas found to have a very small Contribution to explaining the variance in predicting Hb (Xu andZhang 2009). Second, both t: he volume of water above breach invert, Vw, and the depth' ofwater above the breach invert at the time of failure, H, (where Hw = normal maximum reservoirlevel of 1,11i0 feet 'msl. minus Hb) are functions of Hb and so if the reservoir shape coefficientwas included as a control variable then H~b would appear on both the left and right sides ofregression equation.Best Simplified prediction equations were obtainedl through a stepwise regression procedure inwhich regression equations with .different combinations of the five contr~ol variables weredeveloped for each breach parameter. This is a standard method in regression analysis (Haan1977) with the goal of striking a balance between prediction accuracy and simplicity in theequatiOn (i.e. fewer control variables). The equation that has the highest adjusted coefficient ofdetermination, zRoaj, is selected as the best simplified equation, where R~dj is defined as follows:n--i)R2 -k :(5)in which:n = number case histories for which data are used in the regression.analysis.= 'coefficient of determinationk = number of control variables used in' the 'regressiOn analy sisThe (unadjusted) coefficient of determination, R2, is less for the selected best simplifiedprediction equation than for. the best exact prediction equation for the same. breach parameterbecause fewer independent or control variables are included. Hence the best exact predictionP A 6E -6

-fl.. p.~ f..9 .* l.. sr n.i m SE* ScaRn .5. _ .-.,r -.* l*auamvu * * -- Uw vleu lmV llma 11 IIV Vl IIII. " ,APPENDIX Bequations have greater prediction accuracy because they explain a greater fraction of thevariability between ,values of each breach parameter across the case histories. However, thestandard error-of the regression for the best simplified prediction equation, and hence the widthof the confidence intervals for breach parameter estimates, is less than for thle best exactprediction equation for the same breach parameter. This is because there are more degrees offreedom when fewer regression coefficients are estimated because, there are fewer controlvariabres. Another factor that may further decrease the standard error of regression, s2, is thatadditional case histories may be available tO use in the regression when. there are fewer controlvariables because for some case histories estimates were. not available for all five controlvariables as required ifor the best exact prediction equations.The-XU and Zhang (2009) best exact and best-simplified prediction equations for all five breachparameters are presented in terms of the estimated values of their regression coefficients in Tables B.1 and B.2, respectively. These tables also include the standard error of theregression, which-can be Used to calculate confidence intervals for breach parameter estimatesin addition to median predictions that are obtained directly from the regression equations.Xu and Zhang (2009) conducted a comparison with two breach prediction methods (Bureau ofReclamation 1982 and 1988 and Froehlich 1995a and b) and demonstrated that their methodprovides a lower bias and standard error on predictions than these other methods. They admitthat since this comparison used data on which their, model is based it may have had anadvantage over other models included in the comparison, but they nevertheless claim that thecomparison iS fair.Xu and Zhang (2009) included two applications of their equations .to actual dam breaches for..Banqiao and Teton dams. Banqiao Dam was an overtopping failure and Teton Dam was apiping failure.. The predictions are comnpared with the Observed values of the breach parametersfor both the best exact and the best simplified models in Tables 7 and 8 of their paper,*respectively. They also include lower and upper bound estimates based on a 95% confidenceinterval. The theoretical meaning of this confidence interval is that there is a .95% chance thatthe :true values of the breach parameters are *contained* in the range ,between the lower andupper bound values. The lower and upper bound values for an additive (linear) regressionmodel for breach depth are equally spaced on either side, of the median, estimate and this canbe seen, within the limits of round off in the estimates, as shown in Tables 7 and 8 of the Xu andZhang (2009) paper. However, .the spacing between the median estimates and .the lower andupper bounds for the remaining, four breach parameters is very *asymmetric due to themultiplicative (non-linear) form of the regression models for these parameters as explainedabove. Specifically there are approximately two to three and a half fold differences between themedian and lower bound estimates compared .with between .the upper, bound and medianestimates for these breach parameters.. Clearly the widths of the 95% confidence intervals arelarge for all breach parameters. We return to the topic of the confidence intervals on the Xu andZhang (2009) breach parameter estimates in Section B.5 where we discuss how they applyspecifically to the Jocassee Dam breach parameter estimates that. are the focus of this report.PAGE 8-7

,....:...., LL L.,, 1Z' ..Z DIL t.SiLL T .... ~f 3.flCdqIAPPENDIX BTable B.1. Summary of the five Xu and Zhang (2009) best exact regression equationsBreach Parameter Number 'Control bO h 2 b1 b2 3 l b2 bl b21 b3S2vlx(OrVariables b0 b 2 b 1 1 b3r b31 42 b 1 b2 S 1Y(orlogv) ofCases [1gnnlna (orlog b0) ____._______ Reservoir ____Dam Type _________ rdibi~lty Care lorInecpt Ht Sh~:Core Wall CFRD Homog overtop .Piping High Medium Low______Coef., ___ ZonedHb/Hd 66 Xl,2,3,4,S 0.453 0.023 0.000 0.143 0.1,76 0.132 0.218 0.236 0.254 0.168 ,0.031 0.350 0.01254 lnX1,2.3,4,S 0.060 :0.092 0.308 0.061 -0.089 0.299 -0.239 0.4Ul -0.062. .0.289 0.620 0.169Iog, (Bove/Hbj 43 lnXl,2,3,4,5 -0.240 0.133 0.662 0.026 -0.226 0.148 -0.389 0.291 -0.391 0.648 0.184fogtQp/VgVw5/3) 34 InX1.2,3,4,S -1.744 0.199 -1.274 -0.S03 -0.$91' -0.649 -0..705 -1.039 -0.007 -0.375 -1.362 0.0 0.365log(TJ/Tr) ,2.8 InXl,2,3,4,.5 -1.190 0.707 1.22g -0.327 -0.674 -0.189 "-0.579 -0.611 -1.205 -0.56.. 0.579 0.793 0.365Table B.2._Summaryof the five revised Xu and Zhang (2009)_best simplified regression equationsB e d P a a e e N u b r C o n tro l $O11 2 y1lx (o rrecPaaee Nuer Variables bO b b2 b31 h32 b33 b41. b42 b51 bS2 b53 R24 gy~xVY(orliogY) of Cases: !~:nnier (or log hO) I $2I Il.............. ..... .... .......Reservoir -.DamTvpe _ _ __ _ _ __ErodibilltyCate [ry ._Intercept H-gt Shape CoroWalogRDOvertop Piping High Medium Low___________________Coef. __ore_ Wall __ -*R ,ZonedHb/Hd 71 Xl,5 03729 -0.025 ,. _ {0.343 0.257J 0.129 0.314 0.011Ioq(St/Ilb) 61 linX24,4S -0.004 0.558 ___ __ 0.258 -0162 .0.377 -0.092 -0.188 0.584 0.159Ioq(Save/Hb) 53 InX2,4S 1.713 0.739 ___ __ -1.207 .4-.747 -0.613 .4.073 -1.268 0.669 0.173lop(QJp/VpVwSI3) 39 InX2,4,5 2.--020 1.276 -______ ___ -0.788 :-1.232 -0.089 -0.498 -1.433 .0.777 0.304(otl~i/Tr) 30 -1.593 0).654 1.246 ___ __ ______ -1.375 -0.828 0.310' 0.727, 0.288*P A E .B-8" APPENDIX 8B.5 Implementation for Jocassee Dam -Xu and Zhang Breach ParameterEstimates ..As described in our February 2013 repOrt (Ehasz and Bowles 2013), we applied the Xu andZhang (2009) regression equations to the Jocassee Dam to obtain the estimates of the breachparameters for a sunny-day piping failure. We also estimated the confidence intervals for theestimated breach parameters. These were calculated using the values of the standard errors ofregression published by Xu and Zhang (2009) in Tables Bl.1and B.2 and the equations for theconfidence intervals for a multiple regression that can be found in many textbooks (e.g. Haan1977). To verify our spreadsheet for applying the Xu and Zhang (2009) regression equationswe first .reproduced, within a small round-off error, the median and confidence interval estimatesthat are presented in the. Xu and Zhang (2009) paper for Teton and Banqiao dams. We alsoclosely matched estimates made independently by HDR for the Jocassee Dam as shown in ourFebruary 2013 report (Ehasz and Bowles Values representing the Jocassee Dam were assigned to the five control (independent)Variables in the Xu and Zhang (2009) regression equations as follows:* Dam height, Hd = 385 feet.* Reservoir shape coeffiCient, Vw113/Hw, in which V.w is the volume of water above breachinvert based on the stage-capacity relationship for Lake Jocassee evaluated betweenthe normal maximum reservoir level of 1,110 feet msl. and the elevation of the breachinvert [i.e. crest elevation of 1,125 feet msL. minus breach depth Hb and the depth ofwater above the breach invert at the time of failure=, Hw (iLe. normal maximum reservoirlevel of 1,110 feet msl. minus breach depth)]. Both VAw and Hw are calculated using thepredicted values of breach depth obtained from Xu and Zhang (2009). The LakeJocassee elevation-area-storage volume was obtained from Jocassee DWG No. J-17.*Dam type selected as ho~mogeneous/zoned-fill, which iS. the dam type that includesrockfill dams in the Xu and Zhang (2009) methodology.* mode selected as seepage erosion/piping,* Dam erodibility assigned as the low erosion category.The low erosion category was assigned based on the characterization of the Jocassee Damsummarized in Section 3.1 and the descriptions of the erosion categories from Briaud (2008)contained in Figures 4,ia and b. The Jocasee. Dam is desioned and constructed as a moderndam Wit veW deser7)(F)dam wth vry dese -core ~zone. The assignment ofthe 'low erosion category for Jocassee Dam for application of the Xu arnd Zhang (2009)methodology was subsequently confirmed by Professor Briaud as detailed in Appendix A andsummarized in Section 4.3.Table 8.3 shows the input values and the breach parameter estimates from our application ofthe original Xu and Zhang (2009) methodologY to the Jocassee' Dam. Separate breachparameter estimates are included for the best exact and best simeplified prediction regressionP A GEB-9

('~~sugorw ~sour~r; ~ L~rxn~xj rz~r piess;:3. 1~ F¶ ~J~APPENDIX BTable B.3. Breach parameters estimates from Xu and Zhang (2009) application to________________Jocassee Dam.Brah aamtr rsinBest Exact Prediction Best simplifie d predic.tion,Eoin,95% Confidence interval Mein95% Confidence IntervalBehPaaee ,Category *Median Lower' Upper Mein Lower .UpperHeight of breach, Hb ft, Low 253 18, 337 .761 334Failure time, Tf hrs. Low' .'1°( F iBreachb top with, St ft. -Low 701 306 5 1,606 55566 299 _ .1,485Averge reah wdth Sav ft Lb 56 24 1,36 55; 23 ,19Avrg ra~ width, Ba-A.eft--..w-.566-----------------S--.22-.... 1,193Pekot oo t/e. Low (bx )()Fequations. A more-detailed version of Table B.3; which includes the values calculated for allregression parameters and references the regression equation numbers for the equations thatwe used from the Xu and Zhang (2009), paper, is contained in Appendix B of our February 2013report (Ehasz and Bowles 2013).From Table B.3 it can be .seen that using the low erodibility caamn.the best exact prediction*equations, the median failure time is estimated to be aboul" --" J the median, breach topwidth about 700 feet, the. median average breach width about 570. feet, hemedian (or mean)breach depth about 250 feet, and the median peak discharge unde (t)(7)(F) Icfs. Estimatesbased on the best simplified prediction equations are smaller for all parameters except thebreach depth.The 95% confidence interval estimates for 'each breachi parameter are shown in Table B.3 aslower and upper bound estimates that define the confidence interval both below and above themedian estimates. Similar to the examPles for Banqiao and Teton dams, which we discuss inSection B.4, the asymmetry in the confidence intervals can be seen for all breach parametersexcept breach depth, which is symmetrical because of the additive form ,of the regressionequations for breach depth as explained in Section B.4. The symmetry in breach parameterestimates for breach: depth and the asymmetry in-estimates for failure time, breach top Width,and average breach width can be seen in Figures B.3a and b. In these figures the confidenceintervals for breach parameter estimates for Jocassee Dam are plotted as a ratio to the medianestimate for the Xu and Zhang (2009) best exact and best simplified prediction equations,respectively. The asymmetry 'in the confidence intervals for failure .time,, breach top .width, :and-average breach width can -be seen by the longer lines above the-median estimate. (plotted at-aratio = 1.0 shown by the blue dashed line) than b eiow the median estimate.In Table B,3 we have placed boXes around the values ,of the breach parameters that werecommended in our February 2013 report (EhasZ and Bowles 2013) as being most applicable.to the Jocassee Dam. These were ,used in deVeloping the HRR breach hydrograph submittedto the NRC by Duke (2013). They are median estimates based on the low erosion category.P A 6 E B-IO t.LappU fp.. aflaa.. ...TpLpUIt. l. .ql lLll I.I#IfdlN..pppit.J.* -WI E~drLI tsfla~FI 5St.~dR* JLdESUJ, Us~.at*mISd~.6SU c8.l = Prt, t E u EI ,ar. .fJEdllAPPENDIX BBest Exact Prediction4.03.5 .-" ..3.OE 25S2.0___ _____ I_____£1.0 ' "'S0.5 ..Height of. Failure time Breach top Average Peak outflowbreach width breach .widthBreach Parametera) Best exact predictionsBest Simplified Prediction4.0 ".: 3.5 "..~3.o ........~2.5' ~2.0.. ..-10.5 ..Height of Failure time Breach top Ave rg. Pa ufo*breach width bread wdt*Breach Paramneterrage,h widthoutflowb) Best simplified predictionsFigure B,3.* Relative Width of confidence intervals for the original Xu and Zhang (2009)breach parameter estimates for Jocassee Dam expressed as a ratio to the medianestimate (ratio = 1.0).-P A 6 E B-il

/ ' APPENDIX BThe basis for using low erosion category is explained ,above in this section. The basis for usingmedian estimates is discussed below. *The Xu and Zhang (2009) median and confidence interval breach parameter estimates have thefollowing bases:*Median estimate: Predicted values from applying a regression .equation whosecoefficients have been estimated to minimize the sum of the squares of the differencesbetween the predicted values associated with the regression equation .and the observedvalues. All predicted values, excePt for breach depth, must be transformed using a logtransformation to their natural space as shown in Equation 4. The resulting regressionequation represents or "explains" the fraction, R2, of the variability in the observedbreach parameter values in the data, set of historical dam breaches in terms .of thevariation in the observed values of the control variables that were uSed to derive theregression equation in the space in which the regression analysis was performed (i.e.natural space for breach depth and log transformed for all four other breachparameters). Thus *a regression equation that perfectly fits the observed breachparameter values would have an R2 value equal to 100%.*Lower and upper bound estimates (Confidence interval): Based on the variabilitybetween observed breach parameter values in the data set of historical dam breachesthat is not or "unexplained" by a regression equation. This unexplainedvariability is the fraction, (1 -R2), of the variability in the observed breach parametervalues in the data set Of historical dam breaches in the space in which the regressionanalysis was perfOrmed (i.e. natural sPace for breach depth and log transformed spacefor all four other breach parameters).Graphically one can picture the unexplained viariability in breach parameter estimates as beinga scatter of points representing the observed breach parameter values about the regressionline. A key question is, "Where would one expect Jocas see Dam to fit in the range of the scatteror unexplained variation of breach parameter values for the data setof historical dam breachesused by Xu and Zhang (2009)?" Based on the fact that the Jocassee Dam is a well designedand constructed rockfill dam, which has incorporated modern design criteria and defensivedesign features (see Section 3.1), the breach: geometry parameter estimates are expected to bein the range between the median and lower bound estimates. Additional factors that Supportthese ranges of geometric breach parameter estimates include the following:*Uni-directional breach formation: A breach from the. very unlikely failure mode ofpiping through the foundation in iwould, start high On thJCb(F(r ofthe Jocassee Dam and can only progress downwards and laterally towards the center ofthe dam in contrast to developing in two directions as is the case for most historicalbreaches. This would be expected to reduce the width of the breach because of thegreater erosional resistance of the stable (b)(7)(F) iof the breach. InPA$G E B-12 owuruIy i,,,u,.uwuur "5', ,U;, ,5u ,-,v,u,, 13, v. ,. b.o;JAPPENDIX B~addition it would be expect to slow the rate of breach development and reduce the peakbreach flow rate.Deposition of eroded rockfiil material and development of tailwater: The rockflulmaterial moved by the breaching process would ravel downstream by the flow throughthe breach and much of this material would be deposited within a short distancedownstream of the dam. This would cause a significant taliwater to develop that wouldreduce flow velocities through the breach thus inhibiting both downward erosion andlateral development-of the breach with the result that a narrower and shallower breachwould be formed, taking a longer" time to form, and resulting in a lower peak breach flowrate.The combination of all these considerations provides strong evidence that the use of medianvalues of breach geometry parameter restimates for the Jocassee Dam would be a conservativechoice. TherefOre we would expect that realistic breach' geometry parameter estimates for theJocassee Dam would be in the range between the median and lower bound estimates obtainedfrom the Xu and Zhang (2009) regression methodology.Similar arguments to those made for breach geometry parameter estimates for the JocasseeDam being in the range between the median and lower bound estimates can be made for failuretime,, except that theY would support a failure time 'estimate between the median and the Upperbound estimate. Therefore, the use of the median estimate for failure time is also considered toprovide a conservative esti mate of the failure time as defined by Xu and Zhang *(2009).It follows from the same reasoning as discussed above for the breach geometry parameterestimates and the failure time estimate for the Jocassee Dam, that the peak breach flowestimate would be expected to be in the range between the median and lower bound estimatesobtained from the Xu and Zhang (2009) regression methodology.Before the breach parameter estimates can be used in the. HEC-RAS simulation, model for theJocassee Dam, the definition of failure time in Xu and Zhang (2009) must be fully understood sothat it can be appropriately used in the model. This is addressed in the following subsection.B.6 Implementation for Jocassee Dam -Use of Xu and Zhang (2009) FailureTime Estimate in HEC-RAS ModelIt is important that the definition of failure time.l used by Xu and Zhang, (2009) is taken into*account when using failure time estimates from. their methodology in the HEC-RAS. breachmode~l because this definition is different to the definition that is corrmonly used. (e.g. FroehlichI!995b and 2008). This relates directly` to the fifth question raised by the FERC and NRC (seeSection 2). In this subsection we explain how the Xu and Zhang (2009) failure time definitiondiffers.from the definition used by others (e~g. Froehlich 1995b and 2008) and how that wastaken into account in the HEC-RAS breach model for the Jocassee Dam.P A G E B-13

~rru-ry YW7F¶IV~ rnr~r~r:on w:rnnca r.-crr p'::ie Ir:3s:30u:8 ,sr 7U L~fl L3UU;~JW fAPPENDIX BFor the purpose of this discussion, Figure B.4 is adapted from the Xu and Zhang (2009) paper.It illustrates, for a seepage/erosion/piping failure mode, the distinction between the breachinitiation and breach development phases of the breaching process. Outflow during the breachinitiation phase is small, and in the case of a piping failure it is the flow through a developingpipe or seepage channel. As commonly defined the time for the breach development phase isthe time that the embankment would take to washout after the internal erosion process (piping)advances far enough to form a cavern within the downstream shell of the dam leading to acollapse of a portion of the downstream shell that exposes the core and results in a partial andprogressive collapse of the core, exposing it to overtopping. The overtopping would thenwashout the em bankment.80000A: Outflow repidly Increased[- C.. B: Dam crest collapsedE.60000 C: Peak outflowBreach Initiation Breach Dev lo nt. C: Breach fully formedPhase (Xu and Phase (Xu nd Zha g)SZhang) \,A Iharea BIDeveaopontPhase ',-- 20000[I B Developr(F nt ich)s10 a.m. 11 12 13 p.m. 14 15 16Time (hour)Figure B.4. Definition of breach phases in Xu and Zhang (2009) compared with Froehlich(1995b and 2008) illustrated for failure of Teton Dam [Adapted from Xu and Zhang (2009)].Figure 8.4 shows the example of the breach outflow hydrograph for the piping failure of theTeton Dam in 1976. Xu and Zhang (2009) were based on breach development time as definedby Wahl 2004 which states "breach development begins when a breach has reached the pointat which the volume of the reservoir is compromised and failure becomes imminent. During thebreach development phase, outflow from the dam increases rapidly. The breach developmenttime ends when the breach reaches its final size." According to the Xu and Zhang (2009)definition, the time of 10:30 a.m. is a critical point where failure becomes imminent and this timeseparates the breach initiation phase (ending at point A) from the breach development phase(between points A and D). After 10:30 a.m. (point A) the rates of discharge and erosion ofembankment materials from the pipe outflow increased more rapidly. After the collapse of thedam crest at about 11:55 a.m. (point B), the breach developed rapidly due to overtopping of thecollapsed dam crest and soon a peak discharge at about 12:15 p.m. (point C). According to Xuand Zhang (2009) the failure time associated with the breach development process, Tf, wasapproximately 4 hours4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months starting at about 10:30 aim. (point A) and ending at about 2;30 p.m.(point D).Many authors, including Fell et al (2003), point out that it has not been possible toidentify the starting time for internal erosion associated with piping, and so it has not beenP AC B-14 Cct2 " ... .. ........r- L,;;A. uY~,;; *~ p.r ,u ,h~u(oJAPPENDIX Bpossible to estimate breach initiation phase times for historical dam breaches. indicated inFigure BA4, it is the breach development time, Tf, 'between points A and D that is the predicted"failure time" in the Xu and Zhang (2009) method. However, this definition of failure ,time differsto that used 'by others, such as Froehlich (1995b and 2008). and Wahl (2013), in which breachdevelopment time4.is. defined as the period of higher outflow between points B and E: in FigureB3.4, or about 1-.25 hour2.893519e-4 days 0.00694 hours 4.133598e-5 weeks 9.5125e-6 months s5.Specifically, the more commonly-used definitions of breachdevelopment time are as. follows:the 'time from the beginning of rapid growth of a breach to the time when lateral erosion has stopped (Froehlich 1995b)* the needed time from initiation of a breach until it has reached its maximum size(Froehlich 2008)* the time from when the active erosion front reaches upstream face of dam to when thebreach has enlarged to its maximum size (Wah1 2013)From Figure 8.4 it is clear that the Xu and Zhang (2009) definition of breach development timeis a longer :period of time (points A -D) than the more commonly-used definition (points B -E).The importance is not so much that there are differences between the way that failure time isdefined in Xu and Zhang (2009) compared with other methods, but rather that the way thatfailure time is applied in a breach model (e.g. HEC-RAS),should be consistent with the definitionthat, underlies its estimation. Achieving this consistency is discussed next for the application tothe. Jocassee Dam.To achieve a compatible implementation of the Xu and Zhang (2009) breach parameterestimates in HEC-RAS, the.Xu and Zhang (2009) median breach failure time (between points Aand D) and median breach geometry estimates were input to the HEC-RAS model. The XuandZhang (2009) median, peak breach flow rate estimate was: then closely matched by iiterativelychanging the orifice coefficient to a final value of 0.1, the breach weir coefficient to a final valueof 2.0, and the rate of breach progression relationship between points A and D to the final curveshown in Figure' B.5.Figure B,5 contains the breach hydrographs obtained by HDR for a piping failure of JocasseeDam using the Xu and Zhang (2009)-~breach parameter estimates presented in Section BS.5Specifically, this figure includes hydrographa for the Jocassee headwater hydrographrepresented by the blue line (left rscale the Jocassee tailwater hydrograph representedby the brown line (left scale

1,000), and the Jocassee breach idischarge hydrograph isrepresented by the green line (right scale) at a location immediately downstream of the internalboundary in HEC-RAS model that represents the Jocassee Dam. The, breach progressionrelationship, which is a required HEC-RAS input, and which was* developed iteratively as4 'in this report the terinsbreach development lime and breach formation time are used interchange-ably.sIt isnoted that, if the breach :development time i~s estimated using a: triangular, hydrograph based on the peak flowrate and Volume of water released from, the reservoir Using Equation 6 (see Section 6.2.8), then the estimated breachdevelopment time is 2.5 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months , which corresponds to the time between points B and D on Figure B.4.P A G 5. B-15 APPENDIX B1Lb)(7)(F)Figure 6.5. Jocassee Dam breach progression relationship and breach hydrographsfrom the HRR (Duke 2013)described in the previous paragraph, is shown by the black line (left scale). Points A, B and Dare equivalent to points that are defined in Figure B.4.The final values of the orifice and weir coefficients of 0.1 and 2.7, respectively, appear to bereasonable in terms of representing flow through the rockfill material and flow through thebreach following collapse of the dam crest of the rockfill dam, respectively. In addition the formof the resulting breach hydrograph also appears to be reasonable for a piping failure mode andthey closely match the Xu and Zhang (2009) median peak breach flow rate estimate. Point Arepresents the beginning of the failure time as defined by Xu and Zhang (2009) and is thebeginning of the HEC-RAS modeling of the enlargement of the pipe. The breach progressioncurve was adjusted to keep the flow rate to a reasonably low magnitude prior to the collapse ofthe pipe and the onset of overtopping that is simulated at point B on Figure B.5. This pointmarks the end of the breach initiation phase as defined by Froehlich (1995b and 2008). Point Don Figure B.5 marks the end of the breach development phase as defined by Xu and Zhang(2009). The time between points B and D is longer than that estimated by other breachparameters estimation methodologies, but as is discussed in Section 6.5, the longer time isreasonable given the volume of the reservoir contents that must be released while simulating apeak breach flow rate that is consistent with the median predicted val ue.In our February 2013 report (Ehasz and Bowles 2013) we concluded that the breachhydrograph in Figure 8.5 is a realistic but conservative breach hydrograph, which has goodP A GE B-16 APPENDIX Bdefendablity based on the validity of the Xu and Zhang (2009) method, the conservatie naturof the median breach parameter estimates, a piping failure mode initiating in th{r!¶j(F Jthe deposition of rockfill immediately below the dam, .the low erosion category of the rockfihlmaterial, and the various characteristics of a modern dam that were included in the design andconstruction of Jocassee Dam.P A GE B-17 C:.;;.L;';;.:. .. .. .......... ......... ",C.FR 2 r ..........Appendix C-Bench. Marking!/Comparative Analysis I.onralns enzsn.ve unlormauu. -WIvfl.uIU Ilumi puUII,. u'I~ou.IU/J,= puI ,, Appendix C.1Benchmarking Rockfili Dams and Failures KAPPENDIX C.1BENCHMARKINGICOMPARATI.VE ANALYSISThis Section presents the' characteristics of several large embankment dams and describes theproperties and failure conditions and their relevance to-the J ocassee DamBenchmarking Rockfihl Dams and FailuresSome of the large embankment damns that have-failed over the past 50 years are~summarized inthe table at the end of this Appendix 0.1. Although none of these dams are directly relevant tothe potential breaching of the Jocassee Dam, as given by the characteristics of each dam andas compared to the modern design and character of Jocassee, they are the most closely relatedexamples on record.Oros Dam -Brazil 1960* 116 feet high failed by overtopping during construction* Cross-section contained very little rockflhl -just outer zones* Contained mostly sandy shell and sandy lean clay core** 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months to initiate breach and 6.5 to 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months to breach and drain reservoirHell Hole -California, USA 1964* 220 feet high failed by overtopping during constr uction* Upstream sloping core with rockfill shells* Rockfill was dumped rockrfill, no compaction* 29 hours3.356481e-4 days 0.00806 hours 4.794974e-5 weeks 1.10345e-5 months after overtopping initiated 20,000 cfs was passing through .the rockf ill* 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months later the rockfill began to ravel and move downstream.Teton Dam -USA 1976* 305 feet high failed by piping during first filling* Zoned earthf ill embankment, no rockfill*. Pervious rock foundations with voids and irregular jointing* Poor core trench design and treatment during construction* Piping beneath and through-the core for days or weeks* Internal erosion of the core materials leaving large void within core* .Core collapsed into the large void and released the r eservoir=* Once core Collapsed, failure occurred in 2.5+1- hours* Failure was confined to- right abutment where core coIlapsedP A GE Cl!-1 o;::. I 3.Ii~*V ~ -VJILJI ~ ~ ~ J~1 ~n£IUUAPPENDIX C.1Tau m Sauk UR Dam -Missouri, USA 2006* 100 feet high concrete-faced rockfill dam failed by overtopping* Rockfill was dirty, foundations were marginal and slopes were too steep (1.3H:lV)* 10 feet high reinforced concrete parapet wall along crest*- Operated reservoir with high water levels 8 feet up the parapet wall* Poor performance throughout life, large settlements and excessive leakage* Overtopping of a 10 feet high parapet wall initiated slope failure and total failure* Slope failed anld released the reservoir, it w as not an erosional breach* Failure and draining of reservoir Occurred in .less than. 1 hourTokwe Mukosi -Zimbabwe, 2014*e 300 feet high COncrete-Faced Rockfill Dam (CFRD) under construction* Rockflll was compacted and slopes were 1V:1,.3H* Upstream facing was using cast-in-place curb to form upstream slope* Upstream face was-being prepared for concrete facing to be placed last* Extreme flooding when rockfill embankment was 60%.complete(200 feet)* Water level rose to within 5 feet of existing crest* Flood waters passed through rockfill for two weeks without failure,* Local downstream rockfill slopes raveled locally* When flood waters receded, repairs to slopes were made and construction continuedCharacteristics of Jocassee Dam (Modern Center Core Zoned Rockfl~l Dam).-South Carolina, USA** 385 feet high central core zoned rockfill dam* Protective filter and drain zones surrounding the core. zone* Densely compacted rockflll embankment With large rock outer zones and along the toe* Widened core zone along the foundation contact to reduce gradients* Grout curtain along foundation and special core material placement along the contact* Quality control of materials, and compaction.- Extensive instrumentation system and monitoring program* 40 years of acceptable performance and continuous monitoringP A GE C.-2 u----;I-U--- U-- -U -- --APPENDIX C,.1A summary of some of the large embankment dams that have failed over the past 50 yearsolumeBreach-Geomeby (feet) Faue'an Failure Dam Crest V m E roToop lrePeak Failure Tailue .FlrOros Brazi 196 o ne 116 2,034 535,100 ME Overtop 118 656 426 541 340,035- 8.5 8.5Heart:Hoeg US 1964 RockfIt 220 24,800 LE Piping" 185 .574 219 397 259,882 50.0 44.0 6.0Teo Ua97 305 3,100 288,600 ME/HE Piping 285 780 210 495 2,299,.387 4.0 f.5 2.5Taukam US 2005 R.wklieI 100 6,562 4,300 ME ,,100 ,289,000 1.0 1.0Saukwe ____ ___Nobe ____ _____Tow- Zimbabwe 2014 CFRD 300 1;500 No Breach LE NWA N/A N/A NIA N/A NWA /A NWAMukos ________ _________ Failure .... ________ ____ ________NOTES:"The Hell Hole failure was riot a piping failure but was an overtopping of the core and flooding of the rockidil flo 11w through and over the rocidill unti failure"The Taum Sauk failre was caused by a dramatic ten foot overtopping of a parapet wall leading to a failure of the downstream slope and release of the rese~avir.P.A G~E C,1-3

za ZL~3NIJ a

nnieniro mar 7L~ 1--....... Jrrvl--jAppendix C.2Embankment Design Considerations Affecting Failures 3.-ww..q.i. 3....., WJq~~IZ, 3.... ..f. -I .4.. ...-Uge .Agw L....q ,.w..U$. m ~ itt 0lF1 J)APPENDIX C. 2EMBANKMENT DESIGNThe summary of the characteristics of other dams that have failed in recent times, as given inAppendix C.1 clearly outlines the fact that no modern rockfill dam has failed from internalerosion. Oros and Hell Hole dams were both under construction during failure and were failedby overtopping.Oros DamOros Dam was primarily a sand embankment with some rock protection along the outer shellsand is therefore not relevant as a rockfill dam and should not be compared to Jocassee Damsince it is not as robust as Jocassee. Oros would be considered a medium to high erodibilityembankment due to the fine materials that make up both the core zone as well as the sandmaterials within the shells. Due to the very wide cross-section erosion and failure took 6.5 to 12hours.Oros Dam Cros-,,ectionuros usm uvertopping12 hours to Initiate Breach6.5 to 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months to form breach and drain reservoirP A GEC.2-1 APPENDIX C.2Hell Hole DamHell Hole was a rockfill dam, although dumped rockfill, and is the closest example from anerodibility viewpoint to Jocassee Dam. It had an upstream sloping core, and was partiallyconstructed to a level below the adjacent downstream rockfill. The rising waters during theextreme flooding overtopped the lower level core, infiltrated the rockfill and eventually washedout the rockfill in a long and extreme process. The rockfill passed 20,000 cfs of flow for anextended time and with further rising upstream waters the rockfill began to ravel and eventuallybecame unstable, slid downstream due to the excessive flows, formed a breach and failed.The breaching mechanism of rockfill dams, according to the experimental tests on the rockfilldam breaching process performed at the Technical University in Lisbon, Portugal (Franca andAlmeida 2002) as well as the experience and observations at Hell Hole Dam in California, isdifferent from what* is usually described for earth dam failures. The dam failure can be dividedin two distinct phases: before the occurrence of the breach, and after the occurrence of thebreach. In fact, until the moment when the breach develops, the downstream side of the damexperiences damage due to percolation and erosion due to overflow. The turbulent percolationflow induces slope movements, starting from the base of the flow, in an upward evolution until itreaches the surface of the rockfill. The deg~rading process, before the beginning of the breach,has a two-dimensional character and can be compared with typical landslide occurrences. Afterthe initiation of the breach the flow is concentrated on the rockflll section, an eroded channel isformed in the breach direction, and the control section of the breach moves upwards. Thebreach cross-section evolution is due, not only to the continuous erosion induced by the flow,but also to the rock slides that occur from time to time when the equilibrium conditions arereduced. The other important facts observed in the tests and at the Hell Hole Dam failure andrelated to the overtopping failures of rockfill dams are the following:*The flow over the dam induces damage on the downstream slope before initiation of thebreach and influences the initial breach configuration -this damage is mostly two-dimensional sliding along the longitudinal axis of the dam;*When the overflow discharge is enough to induce the initiation of the breach, a majorand sudden slide occurs and the initi al breach appears;*The overflow induces an initial breach width; however, the deposition of the. rock blocksimmediately downstream of the dam has a stabilizing effect, prolonging, the failureprocess -this is reflected mainly in a shallower final breach depth.Thus, a rockfill shell embankment provides more resistance to erosion, even during overtoppingafter the breach is initiated and thus would prolong the timing of the total breach development.Therefore, the Jocassee Dam, which is truly a rockfill dam, will provide the best resistance toerosion and be considered a low erodibility dam.P A GE C.2-2 V~, 3..t .~l.. w ;,uj rlw. ,,FlqrwB~.juvr vw,.aFurrkrfmb wu pawI.uukuuw w r£.1(APPENDX c.2Hell Hole Dam Plan View8*C-s1- 4-7 " )a,,.AA -0.1I IA.. vedhlh460D *b~m .wnd ..0.e notki ...The kr,@ n7e'S6... ... ..... ... ..... .......... 2 5NqMmi Abmmmb@.WJ- 1wbeba. d. 065 mi Hell Hole Dam C rosa-SectionPAG;E C.2-3 APPENDI C,Failure of Hell Hole DamConstuto of Hell Hole Dam on the Rubicon River in Plae County, California began in1984. The dam failed during construction when the partially completed embankment wasovertopped by a flood that was twice as big as the maximum flood of record.The water emergingdownstream rocklhilDecember 22, 1964.eroded.from the toe ofthshell at 3 pm onSome rock has beenBy 7 am on December 23rd, the flow hadincreased as the reservoir rose behind thedam, and a considerable portion of thedownstream slop had been eroded away.At 9:30 am on December 23rd, a gully hadbeen eroded across the crest of the dam, andthe reservoir began to spill over the top of thefill. When this happened the velocity of flowand the rate of erosion increased rapidly, andsoon a major portion of the embankment waswashed away and the reservoir was emptied.At 3:30 pm on December 23rd, there was agaping hole in the dam, and very little water inthe reservoir.i --4IIP AGE C.2-,4 APPENDIX C. 2Teton DamTeton Dam was essentially a homogeneous earth embankment dam constructed with the localwind-blown silts and sands and was therefore highly erodible. The outer slopes were somewhatprotected by a mixture of coarse gravels and sands, which are highly erodible materials. Thedam was founded on very porous rock conditions and contained voids and open jointing withinthe rock formations. Due to the poor design, foundation treatment and construction within thecore trench and along the foundation contact, these factors facilitated piping of the corematerials into the downstream rock formations. The movement and removal of core materialscontinued, over a period of weeks and carried large volumes of core materials away from thecore zone. This process was focused especially along the right abutment and caused a largecavity to be formed within the core of the danm (Osum 2013). That section of the core eventuallycollapsed as more and more material was removed and deposited within the rocks below thesurface of the dam. This phenomenon was unnoticed during the core removal process. It wasonly when the removed materials began to fill the downstream voids that the flows exited alongsurface at the right abutment and began eroding the embankment itself.The piping flows that carried the materials from the core rapidly increased and large amounts ofwater and soil materials exited from the face of the embankment. The local staff attempted tointervene by having bulldozers try to fill the developing openings and restrain the developmentof the openings, but to no avail. With the continued removal of materials the right abutmentimploded into the large void that had formed within the core and the crest of the dam droppedinto the opening.This exposed the reservoir; a major breached developed, washed out the right abutment of thedam, and drained the reservoir. The unique undermining of the core by piping materials into thedownstream rock voids was unnoticed and eventually formed the large cavity that collapsed.That collapse of the embankment into the void caused a premature collapse of the embankmentleading to the breach. T his premature collapse caused the dam to breach faster than if it Were toform the breach by an erosion process. Thus, from a materials standpoint, and considering thefoundation failure mechanism, and the rate of failure, the Teton Dam failure is not comparable tothe rockfill materials, rate of erosion, and foundation geology at Jocassee Dam.P A 6 C.2-5 A PPENDIX C. 2010. 01~rl,~ -a.s. 0'? Sane tl.~;. ,.0~d nd r~~":;~ 54.S.c4.1 tOed. Q.*e.. end~ MOc.Ifoneoo. 1.11 hdn el .0-CeO. 0 onJoa,C. 04) 04-0000+/-) Ot~loled ol, ,oeld. Qoete) 0eG F'ag.2. Cros-.oectionl through center portion of ambunzknwn.t r'ound.~d on nl]uviurn.I'-Cres!El 5332S: ripping...OS d ro~tatd3. Typicol crosB-3ection over abutment founded on jointed rhyolito.P AG1E C.2-6 APPENDIX C.2Taum Sauk DamTaum Sauk Upper Dam was a rockflll dam with an impervious upstream membrane. It was adumped rocklill dam designed with very steep downstream slopes of 1.3H:1V and had a 10 foothigh parapet wall along the crest. The rockfill was a dirty rockfill, which means the strength ofthe rockfill was not as high as a cleaner material, such as was used at Jocassee. Although just100 feet high, it settled as much as two feet along various portions of its four mile length. Thissettlement had caused much distress to the reinforced concrete parapet wall and it had to berepaired several times during its operating life. Also, as a result of the embankment settlement,the upstream membrane suffered extreme cracking and eventually the entire upstream face ofthe dam was lined with a HDPE lining to reduce the water losses and improve the stability of theembankment and foundations. During the installation of the lining system a new instrumentationsystem was installed to record the reservoir levels. Unfortunately the system was not anchoredproperly along the interior slope of the dam and it moved during reservoir operations. This gavefalse readings to the operators and allowed the pumps to overfill the reservoir, which resulted inovertopping of the dam. The parapet wall along the crest of the dam was founded on and withinthe dam crest. The overtopping allowed the water to erode the crest along the downstreamfoundation of the parapet wall and caused the wall to overturn and fail. The wall failure causeda 10 foot surge of water to rapidly washout the toe of the downstream slope. This immediatelycaused instability and failed the over-steep slope. Since the downstream slope was marginallystable at 1 .3H:1V it failed very quickly and released the reservoir. Thus, the Taum Sauk failurewas not a typical overtopping dam breach caused by erosion; but instead it was a slope failurethat released the reservoir. Therefore the dam breached very quickly, which is not arepresentative failure by erosion of a rockfill dam. Thus, the failure at Taum Sauk Dam shouldnot be compared to the material quality, slope configuration or failure mechanism that ispostulated for Jocassee Dam. At Jocassee Dam the embankment materials would have to beeroded and thus reduce the section to expose the core to the reservoir and form the openbreach that would eventually fail.1tagM~z~-- -TYA'CAL W*'E JX~7GV 0? ,5~/ND ROCk~ _________Taum Sauk Cross-SectionP AG EC.2-7 APPENDIX C.2Taum Sauk BreachTaum Sauk BreachTaum 3suK BreachP AG E C.2-S oownuecumy ImWnVUton -wwunow rum puu uicar per 1(1 WM LJIU(o)APPENDIX C.2Tokwe.Mukosl DamThe To,,we-Mukosi Dam in Zimbabwe represents the most recent example, February 2014, ofthe low erodibiflty of rockfill dams. The project involves the constuto of an 90 m (300 ft) highConcrete Face Rockfihl Dam (CFRD) on the Tokwe River and forming a large resrviimpounding 1.8 billion cubic meters (1.48 million AF): the larest reservoir in the Country ofZimbabwe .The Owner of the project is the Ministry of Water Resources Development andManagement Harare -Zimbabwe. W~hile the rockfill portion of the dam construction wasapproximately 60% complete (200 feet) an extreme flood occurred in the watershed and theupstream water level rose to within 5 feet of the crest of the rockfill. The construction on therockflll cotnued throughout the flooding of the upstream reservoir and the partially constructedrockfill portion held back the waters while discharging water through the rockfill to thedownstream.Tokwe-Mukosi Dam is a Concrete Face Rockfill Dam (CFRD) under construc'tion. It consists ofcompacted hard rockfill shell and had an upstream sloping transition rock surface in preparationfor the future reinforced concrete facing, when the flood occurred. The dam was partiallyconstructed when the rising waters duning the extreme flooding came within five feet of thecrest, infiltrated the rockfill and eventually washed through the rockfill in a long and extremeprocess. The rockfill passed extreme flows for an extended time (two weeks). With the iongperiod of extreme flows, portions of the downstem slope began reveling but the rockfillembankment maintained overall stability.Thus, the Tokwe-Mukosi Dam, a compacted rockfill shell embankment provided high resistanceto erosion, even during extreme flows through the rockfill, similar to the Hell Hole exampleabove. The dam withstood extreme flows for several weeks and only experienced localdownstream raveling. Therefore, the Jocassee Dam, which is truly a rockfill dam, will providethe best resistance to erosion and can be considered a low erodibility dam.P A GE C.2-9

¶7f'm'~ V~r ~ 't~ '~'iW ,~1t'~ ff'r j~rr TI? VFf I I ?fff(IEJAPPENDIX C.2Tokwe.Mukosl DamConstruction of Tokwe-Mukosi Dam on the Tokwe River in Zimbabwe began in 1989. Thedam experienced a flood during constuto when the partially completed rockflhl portion ofthe embankment was subjected to a flood that raised the upsream level to within five feetof the crest.The water emerging, from the toe of thedownstream rockflhl shell on February 2, 2014.Some rock has been eroded.By February 4, 2014, the flow had increasedas the reservoir rose behind the dam, andeven with the extreme water flows through therockfill it maintained its stability and resistanceto erosion.~Even one week later February 9, 2014, whenthe flows had reduced, the rockflll maintainedits stability and resistance to erosion.~The construction of the rockfill continuedthroughout the flood conditions and when theflood receded the rockfill would be restoredand repaired.P A G C.2-1O APPENDIX C.2The construction of the rockflll continued throughout the flood conditions and as the floodreceded the rockfill was restored and repaired. See the following photos of the various stages ofdamage during the release of the floodwaters:P A GE C.2-1l APPENDIX C. 2P AG6E C.2-12 L.QIIWOn: oeUrUfU Uf.rmllUfWon -WWIIImOW ,Vf pUDllc per TO (;;PH L.3UO'0)Appendix DDetailed DataSupporting Xu andZhang Revisions ti-G I I Idma'maom I-k41 "t4i ailIml~0 #itt af+IIQ ml~lu+ it.5~4lea.~ .4~0ao(+w)11 tit ma 1,4-Vo,4.t 5lintill+.,+--a-w +at'-.3.WI 3.3.u.;' m 3.p.* -..w, -a--~4.-t ~ -~ 'altWI ----"~ ~sa..,~ .~a-'--3. tilt Ia.- a-ma rn.".4.*4* ,'.4 .tt> 11 3. -, in.a a-431Wa--43. insl~-tal.4.3t 43' 3. tea'n>' 14~-, Wlea*5NI K*~Mt~ 314 3. 13.4 S4p.31W 34- sat.-'*44* 14 3. 3.~t3'~.-maK-K -ma--a-~t ~3..4I3 I 141Ilit tat itt 5* ~tt Ittad Lit LitSt StSits sta tat*13 ta¶ ~t tis .is tti tat t'a..[I a ti -~ U at U 54 Itt3' 15 1,itt*2Iaasitt'ati.O.03'3.35WIp3,flitLiIsStIsaata asI I13.13.a.13.tat ii) 31 tat at ~so tat,U~-ii° ~ a.** t .6 ( a I_ i+;ii II+ I.am,+ ,, +t 4aaWmaagqaaW-~m~l a--.IOm...... -- " --" + + Ill I ............. ram, ........ ;

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I~l~L LdP,.....,.JIU.. -- IIIIU Ul~l ...PLJImL. I i-- --.. I.:............. ---j5-..-----I,lwAppendix E.. , -.Mark Morris Review

....... ... h w t £; s ,; IlwIl£.IU 2Appendix Ejocassee Dam: Independent review of breach prediction methodology andsupporting analyses outlined in the technical report:,Validation of HRR Breach Hydrograph for Jocassee Dam:Through an in depth review of the Xu' and Zhang breach parameterestimation methodology. March 2014Objectives:An independent review of the work undertaken to validate the approach taken for analysing thepotential failure ofthe Jocassee Dam was undertaken and is reported This comprised a reviewof the technical report (Validation of HRR Breach Hydrograph for Jocassee Dam) and some of theassociated / supporting material (as referenced in that report). The review was undertaken by DrMark Morris, who has extensive experience of both research .into and industry application of breachanalysis methodologies, see attached resume. The following provides a summary of keyobservations.Observations:I Broadly -because of the nature of breach initiation and growth, it is impossible to predictthe precise way in which a breach might form. Instead, a best prediction may be made,around which the degree of uncertainty and sensitivity should be examined. This is theaipproach which has been undertaken for the Jocassee Dam failure .analyses, which isconsistent with current good practice.2 There are different degrees to which the breaching process might be analysed, ranging frompure judgement, through the use of equations based on historical failure data, through tomore complex predictive modelling. For this analysis, the use of equations based uponregression analysis has been undertaken -and a potential 'flood hydrograph subsequently'bUilt' from this information. This decision defines the broad approach and hence the.degree of detail that may be attributed to the hydrograph prediction and the associateduncertainty in the prediction.3 Over the years there have been many equations developed to .try to predict outflows in theevent of a breach. The accuracy of these depends upon the parameters selected and the dataupon which they are based (i.e. the types of dam, state of dam, failure mechanisms etc). Asignificant advance during the past 10 years has been a move to incorporate a measure ofsoil erodibility within both regression equations and predictive models. This is fundamentalto predicting conditions associated with parti'cular soil types and condition. The Xu andZhang equations are the first time erodibility has been built into such equations, and aretherefore considered current state of the art for this type of analysis (i.e. for using regressionequations to predict'breach failure).4 Validation of regression equations can be undertaken by comparison against real events,controlled events and predictive models (that mnight be considered to more accurately reflectthe breaching process)., In the Jocassee study, an analysis of the development and validationMark Morris i4i' April 2014Markmorrissamuifrance.comPage E-I

, Appendix Eof the XU and Zhang equations was undertaken. This analysis was extensive, covering thenature and quality of the base data used, as well as the method for equationdevelopment. This review was undertaken 'around the table' with the originators of thework, including Prof Briaud upon Who's work the categories of erosion used were based. Itis difficult to see how a mor'e thorough review of the basis for the equation~s could have beenundertaken.5 Inclusion of material erodibility within the regression equations is a key advan~ce, but thenrequires assignment of values of erodibility -in this case, high-medium-low, toappropriately represent the material type and state. The review by Prof Briaud addressedthis important asPect, and provided independent assessment of the likely erosion :categoryfor Jocassee. This approach is consistent with industry good practice for breach analysis.6 In addition to checking the Original data and developmen~t of the predictive equations,.newequations have been developed using openly accessible case data (iLe. excluding Chinesedata which is not available outside of China). This remoyes any uncertainty relating to thequality of this data (even though that issuewas addressed through careful consultation). Tlheresults from the new equations are :broadly consistent with the earlier predictions.7 Having undertaken ~an extensive assessmentof the regression analysis methodology -including development and testing of revised equations based Upon openly accessible data -it is worth remembering that there are practical limitations to'the accuracy with which anyregression equations can predict the breaching process. These have been carefullyconsidered and discussed in the report; if a more detailed analysis of the potenitial processesis required then it* is likely that this would only be achieved through undertaking morecomplex predictive modelling.8 The approach adopted for prediction of the flood hydrograPh makes use of the NEC RASflow modelling software, within which there is a module designed to simulate growth of a.breach and the associated production of a flood .hydrograph. The approach has been to useparameters predicted by the Xu and Zhang equations as input to the HEC RAS breachmodule, and to adjust various breach parameters slightly to match the peak dischargepredicted from the HEC RAS model the Xui and Zhang equation. This approach issensible and allows the creation of a realistic-and representative flood hydrograph. Thereare likely to be some variations in the hydrograph descriptors in comparison to theregression analysis, since the two approaches accommodate different parameters. However,these differences should be within the typical ranges Of uncertaintY as'sociated with: breachprediction. Of all the parameters describing a breach flood hydrograph, the peak dischargeis probably the most reliably predicted, hence tying the t~vo methods via the peak dischargevalue and ensuring that the hydro gr'aph volume matches the resei'voir stored volume helps tolimit uncertainties.Conclusions:The steps taken here to validate use of the Xu and Zhang regression for breach predictionhave been very detailed and thorough. It is hard to see how rnoredetailed analyses could beundertaken to support the recommended results without stepping from the level. of regressionanalyses into more complex predictive breach modelling. The key aspects of (i) basis for theequations and (ii) representing the material erodibility-have both been addressed in. detail.Makmorrls~samuifran.ce.om,~Page E-2 Appendix EMark W MorrisDirectorCompany Samui France SARIProfession Chartered Civil EngineerSpeclailsatlon Flood risk analysis (Dam and river engineering)Emergency planning/ Research coordinationYaofB rt r t6 IKey Qualifications* Dam and Embankment Safety -Dam-break, Embankment Breach, Risk Assessment and EmergencyPlanning -20 years experience in dambrcak analysis techniques, darn sfafety risk assessment and breachformation prediction at National and International levels supporting the development of emergency actionplans. Studies include national and international research into fundamental processes and modelling tools,.prioritisation of operational and research needs ats wvell as consultancy studies,a Flood Defence and Flood Risk Assessment -25 years experience in conducting river engineering studiesincluding desk, feasibility, design and environmental studies of river channels, hydraulic structures and floodplains. Experience in the assessment of flood risk, construction risk and the safety of hydraulic structures.Particular experience has been gained in the risk assessment of weirs and dams leading to fiailure of thestructures and the analysis /prediction of breach develoPment through emban~kments.* Project management, research coordination, training, technology transfer and dissemination -20 yearsexperience in the management,, co-ordination and implementation of international research projects, includingvarious EU funded projects under FP4, FP5, FP6 and FP7. Experienced in the provision of technical courses,workshops and conferences on practical hydraulics and river, engineering and in dissemination of researchfindings and applications to industry through production of industry, guides, workshops and conference events.Specialist expertise in the development of wveb based tools and methods facilitating technical projectmanagement. and project communication and dissemination.Career Summary2011 -present Director, Samui France SARL2001 -2011 Principal Engineer, Floods Group, FIR Wallingford1988 -2001 Graduate to Senior Engineer, Various Groups, HIR Walllngford1987 -1988 Graduate Engineer, Potable Water Dept., Sir M MacDonald & Partners, CambridgeEducation and Professional StatusPhD Breaching of earth embankments and dams. The Open University, 2012BEng Hons (1 st Class) in Engineering Science (Civil), Exeter University, 1987Member of the Institution of Civil Engineers, 1993Member of the Chartered Institution of Water and Environmental Management, 1993Member of the British Dam Society Committee. 1999-2001, 2001-2005. 2005-2011Member of the Reservoir Safety Advisory, Group, 2007- presentReferee for journal publications including ICE and ASCE, 2006 -presentMember of the editorial committee for the BDS Journal of Dams and Reservoirs. 2008 -presentMember of the ASCE/EWVRI task committee on dam / levee break fluvial processes, 2008 -2012LanguagesSpeaking Reading WritingEnglish Mother tongue Mother tongue Mother tongueFrench Good Good ReasonableIISmui F~rance Page 1 's 2,Page E-3 nra,[l@ll, eIguluglwl2-..l -.V.lleIA. Im.... ....t:: ..............Riie~'-Mark W MorrisAnAnnRlxl ICurrent PracticeMark Morris is Director of Samui France sari, an independent consultancy established in France (Haute Savole)focussing upon specialist research and consultancy supporting management of the environment, with aparticular focus upon water. The corc areas of work include specialist consultancy relating to reservoir safety,dam and levee performance (breach), and flood risk analysis and management.In parallel, Mark collaborates extensively on European research projects, undertaking technical roles, projectcoordination and project communication and dissemination activities. Samui France, in conjunction with itssister company in the UK (Samui Design) develops web based tools and systems to support collaborativeworking and technical project communication and dissemination.During 23 years of working at HR Wallingf'ord, Mark developed world leading expertise in dam and leveebreach analyses, leading to the development of the HIR BREACH model, and supporting the more recentAREBA and EMBREA models. EMBREA arose from Mark's recent PhD) studies in'to breach modelling. MarkWaS deputy coordinator of the European FLOODsite project, which supported implementation of the EuropeanFloods Directive. Within this project Mark also managed technical work on flood defence failure modes, andlevee breach, much of which now underpins the fragility curves used to drive the UK Environment Agencysystem risk models. Mark also managed the FRMRCII work package relating to rapid breach-modeldevelopment (AREBA).Selected Dam and Levee Projects2009 -201!3 EUROPEAN FLOODPROBE. PROJECTEuropean research investigating specific processes associated with urban flooding and leveeperformance. Specific research forievees includes the analysis of internal erosion processes, theperformance of vegetation and the use of remote data for reliability analyses2012 DAMBREAK ANALYSIS FOR THE WLOCLAWEK DAM (VISTULA RIVER, POLAND)Provision of expert advice to ARUP UK and ARUP Poland for the analysis of potential failuremodes, breach and dambreak simulation for the Wloclawek Dam, River Vistula, Poland.2011i- 2012 SMALL RESERVOIR RISK CATEGORISATIONWith risk based reservoir safety legislation being introduced in England and Wales thisproject, commissioned by Defra, provided guidance and a simple risk assessment methodologyaimed at owners of small reservoirs such that they could assess the risks posed by theirexisting or planned small reservoirs and hence take steps to minimise those risks throughdesign and / or operation.20!1 -2012 A GUIDE TO RISK ASSESSMENT OF RESERVOIRSFollowing the earlier seoping study, development of a framework- and recommended tieredapproach for risk assessment for reservoirs in England and Wales. The project develops themethodology and produces industry guidance which builds upon the earlier Interim Guide andCIRIA Guide to risk assessment, including current international best practice.2009 -2010 DAMBREAK ASSESSMENT AND EMERGENCY PLANNING FOR KIO KHlO MA DAM,THAILANDProvision of expert advice on dam failure, flood routing and mapping, flood impact analysis, riskassessment and emergency planning for the Thai Kio Kho Ma Dam.2008 -201i1 FLOOD RISK MANAGEMENT RESEARCH CONSORTIUM- FRMRC2Task leader within the Infrastructure work package, developing a simplified breach model foruse within system risk / reliability modelling.2008 -2011 INTERNATIONAL LEVEE MANUALMember of the UK steering committee for the development of an International Levee Manual,providing detailed guidance on the design, construction, maintenance and operation of floodlevees.1. Samul 1rancePae2IAiO4Page E-4 Mark W Morris Appn~ndix F*2008 RESERVOIR TNUNDATION MAPP[NG (RIM) PILOT APPLICATIONTrial application of the RIM methodology to selected dams, highlighting issues with theproposed methodology. Undertaken in partnership with Atkins.2008 RESERVOIR INUNDATION MAPPING (RIM) METHODOLOGYExpert guidance offered on methodology development as part of the project Quality ReviewTeam.2008 INTEGRATION OF THE HR BREACH MODEL AND THE INFOWORKS RS FLOW, MODEL\- The HIR BREACH predictive breach model was integrated into the InfoWorks RS flowmodelling package providing the first truly integrated commercial breach and flow modellingpackage.2007 -2009 DAM SAFETY INTEREST GROUP BREACH MODELLING PROJECTParticipation in this international R&D project aimed at reviewing, evaluating and developing apredictive breach model for industry use. Participation as developer of the HR. BREACH modeland evaluator of models.2007-2008 DEVELOPING A STRATEGY AND PRIORITISED PROGRAMME FOR RESEARCHSUPPORTING UK RESERVOIR SAFETYTo review existing programmes of research supporting reservoir safety, develop an appropriateshort and long term research strategy for the UK and to provide a prioritised list of recommendedactions. This project supports the research programme being established by the EnvironmentAgency through the Reservoir Safety Advisory Group. The research also considers differentmodes and sources of funding to support the research.2006 -2009 MODELLING EMBANKMENT PERFORMANCE (HR BREACH MODEL)Second stage development of the HR BREACH model through detailed analysis of IMPACTproject data and additional research via the FLOODsite project. This development project willenhance the accuracy and capabilities of the HIR BREACH model for use in predicting breachgrowth through embankment dams and flood defence embankments.2004 -2009 EUROPEAN FLOODSITE pROJECT -TASK 4 (FAILURE MODES) AND TASK 6(BREACH MODELLING)Task Leader for FLOODsite Tasks 4 and 6 investigating failure modes for flood defencestructures and breach initiation and growth processes.. Outputs included a definitive collation offailure modes for use in reliability analysis, along with a state of the art review and developmentof predictive breach models.2004 -2009 EUROPEAN FLOQOSITE PROJECT -INTEGRATED FLOOD RISK ANALYSIS ANDMANAGEMENT METHODOLOGIESProject Manager for the FLOODsite Project, for which HR Wallingford is the Co-ordinatingorganisation. FLOODsite is a European Commission Integrated Project under the SixthFramework Research Pr'ogramme comprising an extensive programme of research andapplication aimed at developing, drawing together and implementing an integrated Europeanmethodology for flood risk analysis and management. The project team comprises membersfrom, some 36 organisations drawn from 15 different countries with a total project value, of,-E14M.I ISmwui [r'8otC Page 3 I5 Apri 2OI4Page E-5 Mark W Morris ApnliSelected 'PublicationsMorris, M.W. (2011) Breaching of earth embank~ments and dams. PhD thesis. The Open University.Morris, M.W., Hassan, M.A.A.M., WahI, T.L., Tejral, R.D.,Hanson, G.J. and Teimple, D.M. (2012)..Evaluationand development of physically based embankment breach models. FLOODrisk2012 conference, Rotterdam,Netherlands. 20-22" November, 201'2. .. ...Van Damme, M., Morris, M.W., Borthwick, A.G.L. and Hassan, M.A.A.M. (2012). Rapid embankment breachmodeling. FLOODrisk2012 conference, Rotterdanm, Netherlands. 20-22" November, 2012.Tounnent, R., Morris; M.W. and ROyet, P. (2012). Levee failures related to structure transitions: typology, leveeperformance evaluation and improvements. FLOODrisk2012 conference, Rotterdam, Netherl~ands. 20-22ndNovember, 2012.Morris, M.w., Hassan, M.A.A.M. andvan Damme, M. (.2012) 'Recent impro~vements in predicting breachthrough flood enmbankments and embankment dams'. British Dam Society ! Biennial Conference, Universityof Leeds. 12-15September, 2012."-Morris, M.W., Wallis, M., Brown, A.J., Bowles, D.S., Gosden, I, Hughes, A.K., Topple, A., Sayers, P.B. andGardiner, K. (2012) 'Reservoir safety risk assessment -a new guide'. British Dam Society. 17lIh BiennialConference,,University of Leeds., 12-i.5 September, 2012.Morris, MW.W, Goff, C. and Simm, J.D. (2012) "Current European research relevant to reservoir safety: theFloodProBE and UrbanFlood projects'. British Dam Society 17"' Biennial University of Leeds. l2-15"' September, 2012.Samuels, P.O. and Morris, M.W. (20.102 'ldealised model for flow towards a dam breach', FirSt EuropeanDiiinIAHR Congress, Edinburgh. 4.6" May, 2010.Samuels, P.G., Morris, M.W., Sayers, P;B., Creutin, J.-D., Kortenhaus, A., Klijn, F., van Os, A., Mosselman, E.and Schanze, J. (2010) 'A framework for integrated flood ,risk* man agement', First European, Division iAHIRCongress, Edinburgh. 4-6lIh May, 2010. ..., ..Morris, M.W. and Hassan, M.A.A.M. (2009) 'Breach *modelling research into practice: ConclUsions from theHR Wallingford & European FLOODsiteProjeets', ASDSO Dam Safety 09, Hollywood, Florida, US2009.Tagg, A.F., Morris, M.W., Lumbroso, D.M. and Di Mauro, M. (2009) 'Improved .Emergency Planning andEvacuation through the use ofra Loss of Life Model', A SDSO Dam Safety 09, Hollywood, Florida, US,Simm, J.D., Morris, M.W., Gouldby, B.P.. and Sayers, P.B. (2009) 'Levee fragility and breach growth analysis',ASFPM Conference 2009, Orlando, Florida, US,Morris, M.W., Hassan, M.A.A.M., Ghataora, 0.5. and-Samuels, P.O. (2009) 'Breach formation: Identifying~keyphysical processes to support improved breach numerical modelling', 33rd IAHIR Congress, Vancouver, BritishColombia,Morris, M.W., Hanson, 0.1. and Hassan, M.A.A.M. (2008) 'Improving the accuracy. of breach' modelling: whyare-we not progressing faster?' Journal of Flood Risk Management, Vol. 1 (No. 4), pp. pp. 150-161.Morris, M.W. (2008) 'IThe impact of dambrealc -managing risks', Dam Safety'Management 2008, Nanjing,China, 22-24th October, 2008.Morris, M.W., Hassan, M.A.A.M, Kortenhaus, A., Geisenhainer, R, Visser, Pi. and Zhu, Y. (2008). Modellingbreach initiation and growth. FLOODrisk 2008 conference, September- 2" October, 2008. Oxfiord, UKMorris, M.W., Hughes, A.J. and Buiijs, F (2008). Dambreak and emergency planning: Meeting end user needs.British Dam Society 15"' Biennial Conference, Warwick, Sept 2008.Morr'is, M.W., Hassan, M.A.A.M., Samuels, P.G. and'Ghataora, G.S. (2008). Development of the HR BREACHmodel for predicting breach growth through flood embankments and embankmhent dam~s. Piverflow2008International conference on fluvial hydraulics, 3-5"' September, 2008. lzmir, Turkey.Morris, M.W.,,Hassan, M.A.AM., Buchholzer, Y. and Davies, T. (2008). HR BREACH: Developing a practicalbreach model to meet industry needs. us Society on Danm.s 28"' Annual Meeting and Conference, April 28"' -May 2"d, Portland, Oregon.Mor'iis, M.W., Hassan, M.A.A.M and Vaskinn, K.A., (2007). Breach forrmation: Field tests and laboratoryexperiments. Journal of Hydranlic Research, Volume 45, Extra Issue (2007).II frange Page 4 15' Page E-6

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