ML20053A175

Harriman Dam Performance Evaluation

ML20053A175
Person / Time
Site:	Yankee Rowe
Issue date:	04/30/1982
From:	Harper G, Jeffrey Jacobson YANKEE ATOMIC ELECTRIC CO.
To:
Shared Package
ML20053A168	List: ML20053A167 ML20053A175
References
TASK-02-04.E, TASK-2-4.E, TASK-RR YAEC-1298, NUDOCS 8205250045
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I HARRIMAN DAM PERFORMANCE EVALUATION April 1982 by John P. Jacobson George A. Harper I

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Yankee Atomic Electric Company Nuclear Services Division 1671 Worcester Road Framingham, Massachusetts 01701 I

I 8205250045 820518 PDR ADOCK 05000029 P

PDR

I DISCLAIMER OF RESPONSIBILITY This document was prepared by Yankee Atomic Electric Company and is completely true and accurate to the best of our knowledge, information and belief.

It is authorized for use specifically by Yankee Atomic Electric I

Company, and the appropriate subdivisions within the Nuclear Regulatory Commission only.

With regard to any unauthorized use whatsoever, Yankee Atomic Electric I

Company, and its officers, directors, agents and employees assume no liability nor make any warranty or representation with respect to the contents of this document or to its accuracy or completeness.

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ABSTRACT This report discusses and summarizes studies used for the assessment of the Harriman Dam for SEP Topic II-4.E, Dam Integrity. The conclusion of this assessment, which addresses hydrological, geotechnical, seismic and seepage I

factors, is that the f ailure probability of Harriman Dam is extremely remote.

The dam meets current day safety criteria. Despite these conclusions a consequence analysis has been performed for a hypothetical dam failure as requested by the NRC.

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TABLE OF CONTENTS Page DI SCLA I ME R O F RE S PONS I BILITY......................................

11 ABSTRACT..........................................................

iii LIST OF FIGU RE S AND LIST OF TABLES................................

v

1.0 INTRODUCTION

1 2.0 H I STO RY O F H ARR IMA N D AM...........................................

4 3.0

SUMMARY

OF RECENT PERF0Pl!ANCE EVALUATIONS.........................

5 3.1 Static Stability.............................................

5 5

3.2 Dynamic Stability............................................

6 3.3 Design Basis Flood...........................................

4.0 DAM FAILURE MECHANISMS AND PROBABILITIES..........................

7 5.0 ANALYSI S OF FAILU RE CONSEQUENCE...................................

9 5.1 Methodology..................................................

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5.2 Input Data...................................................

9 5.3 Results of Consequence Analysis..............................

11 5.4 Conclusions of Consequence Analysis..........................

11 6.0 CONCLh) IONS AND AS SES SMENT OF DAM.................................

13 REFERENCES........................................................

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LIST OF FIGURES Number Title Page 1-1 Deerfield River Drainage Basin Map............................

2 1-2 Harriman Reservoir General Area Topography....................

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i LIST OF TABLES Number Page 12 5.1 I

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1.0 INTRODUCTION

Harriman Dam is a large earth dam on the Deerfield River located in Whitingham, Vermont, approximately 7 miles upstream of the Yankee plant at Rowe, Massachusetts (Figures 1-1 and 1-2).

Harriman Dam is an integral part of the Deerfield River hydroelectric system.

Over the past three years, all I

aspects of dam performance have been thoroughly investigated. As a result, the dam was improved in 1981 with a filter blanket which was covered with an impervious layer raising most of the downstream slope about 5 feet. The dam now meets all current day criteria for slope stability, floods and seepage control.

I Yankee Atomic Electric Company does not own or operate Harriman Dam.

The dam is owned and operated by New England Power Company (NEP). Although NEP is a part owner of Yankee, it is a separate corporation both legally and financially, with (1) different ownership, (2) different management, and (3) a I

dif ferent Board of Directors. NEP is regulated with respect to Harriman Dam by the Federal Energy Regulatory Commission (FERC) under License No. 2323.

The legal authority and legal responsibility f or the dam's control rests with FERC under 18CFR12 (Rev. 3-1-81).

I Nevertheless, Yankee has been required as part of the Systematic Evaluation Program (SEP) to make an assessment of the reliability of the dam.

This assessment is based principally on studies performed by Geotechnical Engineers Inc., Winchester, Massachusetts and Chas. T. Main Inc., Boston under I

contract to New England Power Company.

This report provides a summary of conclusions from the most recent studies. The probability of Harriman Dam failure by different failure mechanisms is also discussed and a consequence analysis of Harriman Dam failure is provided even though the probability of failure is shown to be extremely remote.

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I 2.0 HISTORY OF HARRIMAN DAM Harriman Dam (originally known as Davis Bridge Development) is a semi-hydraulic fill earth dam located on the Deerfield River in Whitingham, Vermont. The dam was designed by Albert Crane, and the design was reviewed by I

W.P. Craeger, a noted dam designer of that era.

The reservoir impounded by the dam extends upstream about 8 miles and has a surface area and active storage volume at spillway crest of 2,050 acres and 103,375 acre-feet, respectively.

The reservoir formed by Harriman Dam is an integral part of the Deerfield River hydropower system operated by the New England Power Company and regulated by the Federal Energy Regulatory Commission.

Harriman Hydroelectric Station has a rated generating capacity of 33.6 MU with a I

maximum flow rate of approximately 1,800 cfs through its three turbines.

Originally, Harriman Dam was about 200 feet high and contained approximately 1,900,000 cubic yards of earth.

Harriman Dam has been altered and improved three times since initial completion. The first modification to the dam occurred in 1939 when the dam was raised 5 feet to increase flood storage and dam freeboard.

In 1964, the dam was raised again to its present maximum height of 215.5 feet above the toe of the dam, with a crest length of 1,300 feet and a normal freeboard of 29.5 feet above spillway crest.

I The most recent modification to Harriman Dam was implemented in 1981 to upgrade the dam to current day criteria. The 1981 dam improvement consisted of stripping the downstream f ace, installing a compacted filter drain and placing an impervious blanket on top of the filter [1].

This increased the static safety f actor above 1.5 [1,2].

In addition, as a result of the substantial field investigations, the dam is fully instrumented with 70 piezometers to monitor the pore pressures. This latest improvement raised most of the downstream face of the dam about 5 feet.

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I 3.0

SUMMARY

OF RECENT PERFORMANCE EVALUATIONS Complete and thorough analyses of factors affecting Harriman Dam safety have been performed by New England Power Company and its consulte..ts.

The results indicate that Harriman Dam meets current dam safety criteria and that it presents negligible risk to downstream interests. A summary of New England Power Company's findings are included below.

3.1 Static Stability I

Cross sections of Harriman Dam were analyzed for static slope stability by standard slope stability methods using the simplified Bishop circular arc technique. Data and information used in the analysis included design and construction drawings, geotechnical data including standard penetration resistance and soil classification from borings and test pits, pore pressure data f rom the 70 piezometers, and strength data from triaxial compression I

tests on undisturbed samples from borings. The dam was analyzed for maximum operating pool level,1,392 feet (NEP datum), and for rapid drawdown.

I The dam in its present upgraded state meets current dam safety criteria. The dam has a factor of safety of greater than 1.5 for all potential shear slide surfaces [1,2].

I 3.2 Dynamic Stability I

Analysis of the dynamic stability of Harriman Dam (15] indicates that j

the dam is stable under seismic loads imposed by the Yankee composite spectrum with a peak ground acceleration of 0.lg.

The analysis showed that no loss of strength would occur in the dumped shell of this dam l

significant during or after an earthquake. Shear strains at three locations (crest, upstream slope, downstream slope) at the highest section of the dam were I

estitrated from results of cyclic triaxial tests and shear stresses determined by a one-dimensional analysis using the computer program SHAKE [20]. The estimated shear strains were equal to or less than one percent in all three sections, resulting in an estimated settlement of the dam crest of less than 2

=

feet. Deformations of this magnitude would not affect the overall safety of l

the dam.

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I Based on laboratory tests of undisturbed soil samples from the Harriman Dam shell, the shells were determined to consist of dilative material

[13,15]. Further analysis showed that the shell material would not be subject to liquif action during or af ter an earthquake [15]. Laboratory tests performed on undisturbed samples from the dam core show that the core material is also dilative [12,13].

I 3.3 Design Basis Flood A Design Basis flood (DBF) analysis [16] was conducted to study the potential effects of hidrologic flooding on Harriman Dam and the Yankee site.

This DBF analysis employed a flood hydrograph computer model, HEC-1 [17], to route the Design Maximum Rainfall (DMR) through the 236 square mile Deerfield River drainage basin upstream of the Yankee plant. The model was calibrated and verified using the maximum storms of record on the Deerfield River Basin.

The DMR was determined by the storm transposition method using applicable I

maximum rainfall data from the northeastern United States, rather than from the generalized Probable Maximum Precipitation (PMP) charts. These PMP charts are not appropriate for the Yankee site because they do not account for terrain effects.

I The analysis shows that Harriman Dam does not fail during the DMR, which is 14.3 inches of rain over 200 square miles in 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and 16.0 inches in 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />. The annual probability of occurrence of the DBF was determined to be less than 10-I I

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I 4.0 DAM FAILURE MECHANISMS AND PROBABILITIES Although records of United States dam failures are readily available

[3,4,5], the quality of data is mixed and the class of dams represented is not homogeneous. The dams vary in level of engineering design, maintenance, operational control and other factors.

Furthe rmo re, the definition of failure is inconsistent among studies and the f ailure rates are of ten determined by I

combining dams of highly oisparate characteristics. Despite the shortcomings of these previous studies, the results have been used to determine annual risk of dam failure.

Based on the historical. record, the average annual risk (i.e., the probability that a dam will fail in any one year) for all types of dams is on the order of 10

[6,7,8].

However, as Baecher, et al.,

[6] point out, failure rates are not constant over the life of a dam:

about half the failures occur in the first 5 years of dam life and the remainder more or less I

uniformly over the rest of dam lif The failure rate is on the order of

-3

-5 10 during the first 5 years oi aam life and drops sharply to 10 afterwards [6]. This implies that failure from poor design or poor construction is more likely than failure from extreme environmental loading (flood or earthquake). Furthermore, Takase [9] suggests that structural safety of earth dams increases with time.

Data in Middlebrooks [10]

corroborate this, with dam f ailures decreasing with age.

In other words,

' aged' earth dams perform significantly better than do new ones.

I The annual risk of dam failure can be expressed as the sum of contributions frma the various causative mechanisms related to hydrological, seismic and geotechnical factors.

Specifically, overtopping, seepage or piping, and embankment slides have been identified as failure mechanisms for earth dams.

During the past few years, these failure mechanisms for Harriman Dam have been comprehensively studied [1,2,11,12,13,14,15,16].

YAEC-1207 [16]

has shown that Harriman Dam will not be overtopped and f ail during the Design Basis Flood which has an annual probability of occurrence of less than 10-I Recent studies identified areas of seepage in the dam.

The dam improvement in 1981 included provisions to drain and direct this seepage to I

I ensure that there would be no seepage breakout on the downstream face of the dam.

This recent improvement also raised the static factor of safety above 1.5 [1,2].

Dynnmic stability studies have shown that the dam will not fail if subjected to an earthquake with a 0.lg peak ground acceleration as defined by the Composite Spectrum [14,15]. Also, laboratory tests on soil samples taken from the dam demonstrate that both the shell and the core of the dam consist of dilative material [12,13,15].

Further analysis shows that the shell I

material would not be subject to liquef action during or af ter an earthquake

[15].

These studies document that the probability of failure of Harriman Dam from any mechanism is extremely remote. As Baecher, et al., [6] have pointed out, any dam is most at risk during the first 5 years of dam life. Harriman Dam is not in that category.

Furthermore, Harriman Dam is a well-maintained, I

well-instrumented and vell-inspected dam. All these factors point to the fact that Harriman Dam has a very small probability of failure. As ASCE/USCOLD [4]

point out, " Properly designed, constructed and maintained dams are safe structures." Harriman Dam is indeed a properly designed, constructed and maintained dam.

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I 5.0 ANALYSIS OF FAILURE CONSEQUENCE Even though the likelihood of failure is extremely remote, Yankee was requested by the NRC to perform a consequence analysis to assess the flood potential at the Yankee plant due to an assumed hypothetical failure and I

subsequent breaching of Harriman Dam. A failure mechanism is not postulated because those that have been identified (hydrological, geotechnical, seepage and seismic) all have negligible probabilities of occurrence.

The study was performed parametrically to gain insight into the sensitivity of the flood level at the Yankee site to analytical input parameters. The following summarizes the methodology, input data, results and conclusions of this study.

I 5.1 Methodology The study was performed in three steps using appropriate computer programs. First, a parametric investigation was performed to determine the effect of various breach sizes, breach times, and starting reservoir elevations on the outflow hydrograph from Harriman. Outflow hydrographs were developed using the Army Corps of Engineers, HEC-1 Dam Break Computer Program

[17]. The second phase consisted of hydraulically routing various outflow hydrographs down the valley, through Sherman Reservoir, by the plant and I

downstream just below Monroe Bridge. The routing was accomplished using the DAMBRK Program [18] developed by the Hydrologic Research Laboratory of the National Weather Service.

Finally, the DAMBRK Program was used to determine the outflow hydrograph from Harriman Reservoir because it more accurately models the breach-reservoir interaction. These outflow hydrographs were then routed down the Deerfield River and past the Yankee plant.

I 5.2 Input Data Cross sections used in the hydraulic flood routing were taken off the original topographic maps of the river, circa 1920. The maps, obtained from New England Power Service Company, have a scale of 1" = 100' and a 10' contour interval.

A total of 24 cross sections were used to model a 16-mile stretch of the river from the upstream limit of Harriman Reservoir downstream to Monroe Bridge, approximately 3/4 of a mile downstream from the Yankee plant.

Six cross sections were used to model the elevation-storage relationship and the distribution of storage spatially along the 8.5-mile Harriman Reservoir for an average cross section spacing of 1.4 miles. The remaining 7.5 miles of river, including Sherman Reservoir, was modeled using 18 cross sections for an average spacing of 0.4 miles. Additional cross sections are created by tre model via linear interpolation between specified adjacent cross sections.

Roughness coef ficients were chosen using good engineering judgment.

Manning "n" values used were 0.035 for reservoirs, 0.04 in the river channel, and 0.1 for the wooded overbanks with medium to dense brush. Based on the parametric study, these coef ficients, although important, did not significantly modify the flood wave as it progressed down the river valley.

I Using the HEC-1 Code, starting elevations for Harriman Reservoir were assumed at 1,392, 1,386 and 1,370 feet.

For the DAMBRK Code, starting I

reservoir elevations were assumed at 1,392 and 1,370 feet. All elevations are referenced to NEP datum, which is 105.66 feet below National Geodetic Vertical Datum.

Harriman Dam breach times used in the HEC-1 analysis were 5 minutes, 15 minutes, 30 minutes, 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />. Failure times of 5 minutes and 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> were used with DAMBRK.

" Instantaneous" f ailure was not postulated since earth dams do not fail in this manner. According to a recent report, "The few documented earth dam failures have shown one striking common denominator:

the I

failure is anything but sudden" [19].

The breach of Harriman Dam for use in DAMBRK was a f ull-depth / partial-width breach consistent with past observations of breached earth dame.

The breach dimension was trapezoidal with top and bottom widths of 650 and 100 feet, respectively.

Once overtopped by 2 or more feet of water, Sherman Dam was assumed to

!l completely fail in 5 minutes. This failure time was used because of the f

3 physical dimensions of the dam and the magnitude of the Harriman flood wave. l

I The Sherman Dam breach assumed in the study was a full-depth / full-width breach. Sherman Reservoir pool level was assumed to be at the spillway crest at the beginning of the analysis unless otherwise noted.

5.3 Results of Consequence Analysis Table 5.1 summarizes six hypothetical failure cases which were analyzed in detail using the DAMBRK Program. These cases were chosen to envelope various inputs to the study.

5.4 Conclusions of Consequence Analysis I

o Flooding depths above the turbine building floor ranged from 24.7 feet (Case 4) to 45.4 feet (Case 1).

o The initial condition of Sherman Dam has little effect on the I

flooding elevations at the Yankee plant. Even if Sherman Dam is assumed to be completely removed and the pond empty, the backwater effect produced by the channel constriction at the dam and by the downstream channel backs water up the pond and essentially refills the reservoir. Since Harriman's volume is over twenty-five times that of Sherman Reservoir, there is ample water released from Harriman early during the breach to readily refill ~an empty Sherman Reservoir.

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Use of the more hydraulically correct dynamic reservoir routing method in the DAMBRK Program versus level pool reservoir storage routing reduces the peak outflows through the breached dam by 20% -

25% for Harriman and, therefore, reduces the peak water elevation at the plant.

o Flood elevations at the plant are governed primarily by one parameter:

the initial volume of water in Harriman Reservoir at the time of failure. This conclusion is based on results from both I

the HEC-1 and DAMBRK simulations.

TABLE 5.1 i

Maximum liar riman Peak Discharge Stage Maximum 3

Reservoir (ft /sec) at Velocity Flooding **

Elevation

• Breach Plant

• at Plant Duration Case (feet)

Time At Breach At Plant (feet)

(feet /sec)

(hours) 1 1,392 5 min.

1,708,000 1,157,000 1,068.1 11.5 1.5 2

1,392 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> 1,417,000 1,086,000 1,064.4 11.3 1.5 3

1,370 5 min.

1,256,000 847,000 1,050.0 11.1 1.1

}

4 1,370 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> 1,014,000 808,000 1,047.4 11.1 1.1 5***

1,392 5 min.

1,708,000 1,284,000 1,067.9 11.9 1.2 6***

1,392 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> 1,423,000 1,078,000 1,056.8 11.3 1.2 All elevations are relative to NEP datum (turbine building floor elevation 1,022.7 feet).

• • Time that water is above turbine building floor.

• • • Cases 5 and 6 are for Sherman Dam completely removed and pond drained at the time when Ibrriman Dam breach begins.

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6.0 CONCLUSION

S AND ASSESSMENT OF DAM As a result of the studies summarized here, it is concluded that the failure probability of Harriman Dam, with its recent improvement, is extremely remote. The dam meets current day safety criteria including a static safety factor greater than 1.5.

However, at the request of the NRC, a consequence analysis of Harriman Dam f ailure has been performed and is presented in Section 5.

This analysis showed that the maximum water level at the Yankee plant would be from 25 to 45 feet above the turbine floor, depending on the failure scenario.

As many studies have shown, dams are most at risk early in dam life.

Harriman Dam, built 60 years ago, is a well-maintained, well-instrumented and well-inspected dam.

As ASCE/USCOLD [4] point out, " Properly designed, constructed and maintained dams are safe structures." Harriman Dam is indeed a safe structure.

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REFERENCES 1.

C. T. Main, Inc.,1982, "New England Power Company, Harriman Dam Improvement Project, Final Report".

2.

C. T. Main, Inc.,1981, "New England Power Company, Harriman Dam".

3.

A. O. Babb and T. W. Hermel,1968, " Catalog of Dam Disasters, Failures and Accidents", Bureau of Reclamation, Washington, D.C.

4.

ASCE/USCOLD,1975, " Lessons from Dam Incidents", USA.

5.

R. B. Jansen,1980, " Dams and Public Safety", U.S. Department of the Interior, Water & Power Resources Service.

6.

C. Baecher, M. E. Pate and R. de Neufville,1980, " Risk of Dam Failure in Benefit-Cost Analysis", Water Resources Research, Vol.16, No. 3, I

pp. 4 49-4 56.

7.

E. Venmarke,1974, " Decision Analysis in Dam Safety Monitoring",

Proceeding of " Safety of Small Dams", August 4-9, 1974.

8.

D. Rose, 1978, " Risk of Catastrophic Failure of Major Dams", Journal of the Hydraulics Division, ASCE, Vol.104, No. HY9, pp.1349-1351.

9.

K. Takase,1967, " Statistic Study on Failure Damage and Deterioration of Earth Dams in Japan", Ninth Congress, International Commission on Large Dams, Istanbul.

10.

T. A. Middlebrooks, 1953, " Earth Dam Practice in the United States",

Transactions, ASCE, Paper 2620.

11.

C. T. Main, Inc.,1979, "Harriman Dam Stability Analysis".

12.

Geotechnical Engineers, Inc., 1981a, "Harriman Dam, Summary of Field Investigations and Laboratory Tests for Phases I and II".

1 13.

Geotechnical Engineers, Inc.,1981b, "Harriman Dam, Summary of Field Investigations and Laboratory Tests for Phase III".

14.

Geotechnical Engineers, Inc.,1981c, " Abstract of Stability-Related Data, Harriman Dam".

l 15.

Geotechnical Engineers, Inc.,1981d, " Seismic Stability Evaluation, Harriman Dam".

16.

Yankee Atomic Electric Company,1980, " Design Basis Flood Analysis, I

Yankee Atomic Electric Generating Station, Rowe, Massachusetts",

l Technical Report YAEC-1207.

17.

U.S. Army Corps of Engineers, 1979, Computer Program 723-X6-L2010, HEC-1,

" Flood Hydrograph Package, Dam Safety Version", Hydrologic Engineering Center, Davis, California.

18.

D. L. Fread, 1980, "DAMBRK:

The ?NS Dac:-Break Flood Forecasting Model",

flational Weather Service, Silver Spring, Maryland.

19.

V. M. Ponce and A. J. Tsivoglou, 1981, "Modeling Gradual Dam Breaches",

Journal of the Hydraulics Division, ASCE, Vol.107, No. HY7, pp. 829-838.

20.

P. B. Schnabel, J. Lysmer and H. B. Seed,1972, " SHAKE, A Computer Program for Earthquake Response Analysis of Horizontally Layered Sites",

Report flo. EERC 72-12, College of Engineering, University of California at Berkely.

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