Text

Calculation 15-031, Revision 0, Site Specific PMP and Ancillary Meteorological Analysis.
	ML15162A310
Person / Time
Site:	Monticello, Prairie Island
Issue date:	04/17/2015
From:	Karpinski D; Northern States Power Co, Xcel Energy
To:	; Document Control Desk, Office of Nuclear Reactor Regulation
Shared Package
ML15162A317	List: ML15162A308; ML15162A310; ML15162A312;
References
	L-XE-15-013 15-031, Rev. 0
	Download: ML15162A310 (352)
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0 Unit: r2J 1 D 2 Safety Class: [2J SR D Aug Q D Non SR Special Codes: D Safeguards D Proprietary Type: Sub-Type:

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D EC Number: 25484 [2J Vendor Cale Vendor Name or Code: B & V Vendor Doc No: 180999.51.1008 Description of Revision: Revision 1 The following calculation and attachments have been reviewed and deemed acceptable as a legible QA record Prepared by: (sign) I (print) by Vendor Date: 3/4/15 Type of Review: D Design Verification D Tech Review [2J Suitability Review Method Used (For Only): D Review D Alternate Cale D Test Approved by: (sign)

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Description of Change:

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The following calculation and attachments reviewed and deemed acceptable as a D by Vendor Date:

Reviewed by: (sign) / (print) Date:

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Record Retention: Retain this form with the associated calculation for the life of the plant.

QF0549 FP-E-CAL-01 , 7 4 Cal on ature S This reference table is used for data entry into the PassPort Controlled Documents Module reference tables (C012 Panel). It may NOTE: also be used as the reference section of the calculation. The input documents, output documents and other references should all be listed here. Add additional lines as needed by using the "TAB" key and filling in the appropriate information in each column.

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QF0549 FP-E-CAL-01 , 7 4 le 0 Monticello Specific I DYES IZI Code(s) (See MT Form 3805):

DYES IZI N/A Code(s) (See MT Form 3805): _ __

Does the DYES IZI Require Fire Protection Review? (Using MT Form 3765, "Fire Protection Program Checklist", determine if a Protection Review is required.) If YES, document the engineering review in the EC. If completed Form 3765 to the associated EC.

DYES IZI Affect piping or supports? (If Yes, Attach MT Form 3544.)

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Record Retention: Retain this form with the associated calculation for the life of the plant.

QF0547 FP-E-MOD-11 Rev. 5 u

0 5 Organization Name: B &V PO or

Reference:

00048375 The purpose of the suitability review is to ensure that a calculation, analysis or other design document provided by an External Design Organization complies with the conditions of the purchase order and/or Design Interface Agreement (DIA) and is appropriate for its intended use. The suitability review does not serve as an independent verification. Independent verification of the design document supplied by the External Design Organization should be evident in the document, if required.

The reviewer should use the criteria below as a guide to assess the overall quality, completeness and usefulness of the design document. The reviewer is not required to check calculations in detail.

Design inputs correspond to those that were transmitted to the External ~ D Design Organization.

2 Assumptions are described and reasonable. ~ D 3 Applicabl e codes, standards and regulations are identified and met. ~ D 4 Applicable construction and operating experience is considered. D [g]

5 Applicable structure(s), system(s), and component(s) are listed. D [g]

6 Formulae and equations are documented. Unusual symbols are defined. ~ D 7 Acceptance criteria are identified, adequate and satisfied. [g] D 8 Results are reasonable compared to inputs. [g] D 9 Source documents are referenced. ~ D 10 intended use. ~ D 11 terms the ~ D 12 assumptions, outputs, etc. which are ~ D enforced adequate procedural controls.

13 Plant impact been identified and either implemented or controlled. If not ~ D identified in the document itself, identify and their and descriptions are listed in 14 have been considered D N/C Completed by: .Dariusz Karpinski/ ~-k~,_.~* Date: 4/1/15 I 7 Form retained in accordance with record retention schedule identified in FP-G-RM-01.

QF0547 1 Rev. 5 u

ncc-.r lbi,6......,...., """'16' IPT .

No.

1 2

3 4

5 6

7 8

9 10 11 12 13 14 15 Form retained in accordance with record retention schedule identified in FP-G-RM-01.

QF-0528 Rev.

of 3 NUMBER/ TITLE: 180999.51.1 - MNGP and Meteorological Analysis REVISION: 1 DATE: 3/10/15 ITEM REVIEWER'S COMMENTS PREPARER'S REVIEWER'S

RESOLUTION DISPOSITION

1. Page 12, Paragraph 3.2, Items 1 & 2: Items 1 & 2 Added wording to Concur with state that the site-specific PMP and LIP reference sections resolution.

calculations identified precipitation lower than what where reasons for is provided by HMR-51 & 52, respectively. Aterra differences are recommends providing the reasons why the described.

values are lower than the HMR values and why the calculated values are more appropriate and should be used for the PMF calculation.

2. Page 13, Paragraph 4.4: Wherever possible, add References added Concur with references to support key assumptions, similar to where appropriate. resolution.

what was done for Assumption #6. #7 and #8.

3. Page 13 Paragraph 4.4, Item 1: The first sentence Reworded sentence. Concur with needs to be reworded. resolution.

Corrected in 12-14-2014 revision-track changes edits have now been updated correctly.

4. Page 13, Paragraph 4.4, Item 2: Although Added wording to more Concur with scientific judgment is ultimately used to determine explicitly discuss resolution.

if it is appropriate to transpose a storm, Aterra transposition guidelines.

understands that this assessment is performed following an accepted set of parameters (e.g.

elevation differences of+/- 1,000-feet or distances more than +/- 6-degrees latitude as an initial screen). Aterra recommends adding a bit more detail regarding the framework within which the scientific judqment is applied.

5. Page 26, Paragraph 5.3.4.2: The second Added description of Concur with paragraph states: One of the factors given for reasoning and the resolutions.

determining if a storm is transposable is whether three storms were used the distance from the storm to the MNGP basin at PINGP were not used centroid is more than 6 degrees latitude. In Table at MNGP.

4, the all-season PMP short storm list, the latitudes given for Storm 14W (Cole Camp, MO),

15W (Collinsville, IL), and 9W (Edgerton, MO) are Corrected in 12-14-2014 more than 6 degrees latitude from the MNGP revision-track changes basin centroid. The reason for including these edits have now been storms should be explained. Also, it was noted in updated correctly.

the PINGP calculation that Storms 13W (Council Grove, KS), 3W (Fall River, KS), and 22W Page 1 of 3

for PINGP but these three storms is more than 6 degrees distant from the PINGP basin centroid. The reason for excluding these storms from the MNGP calculation should be explained.

6. Page 29, Table 5: Similar to above, the cool- Added description of Concur with season PMP short storm list, Table 5, includes reasoning. resolution.

Storms 3C, 6C, 7C, 9C, and 1OC which all are more than 6 degrees latitude from the basin centroid. Storm 3C is shown in Table 12 to be the controlling storm for the 72-hour storm that would be used in the PMF analysis for MN51.1011, Rev.

1GP. The reason these storms were considered transpositional and included in the short list for cool-season PMP storms should be ex lained.

7. Page 29, Table 5: It appears that the bottom of Removed track changes Concur with the table repeats the information provided in the version of table to avoid resolution.

top half of the table. Check to confirm that table confusion.

information is accurate and update table as appropriate.

8. Page 34, Figure 10: Figure 10 gives an example Added more description Concur with of the HYSPUT trajectory model results at 700 of how the HYSPUT resolution.

mb, 850 mb, and 960 mb levels for the Ashland, data was used.

WI Storm 2C. It is unclear how this data translates to an inflow flow vector of SSW at 560 miles given in Table 2 of Attachment 2. An explanation would be hel ful.

9. An explanation should be provided for including Good point, a different Concur with the transposition example of the Fall River storm storm has replaced the resolutions.

(3W) to the MGNP basin centroid when this storm Fail River storm used as was not included in the MGNP list of PMP storms. the example. Note, that initially the Fall River storm was transitioned and used and the further evaluations of its transposition limits determined that this storm was not transpositionable.

Corrected in 12-14-2014 revision-track changes edits have now been updated correct!

10. Page 49, Table 6: If the transposition criteria for Like the PMP Concur with LIP storms is the same as the criteria for all- development, a resolution.

season and cool-season PMP storms, an description was added explanation should be provided for including detailing that the Page 2 of 3

QF-0528 (FP-E-MOD-07) Rev. 1 Storms 10W, 19W, 26W, 31W, and 4W. These transposition guidelines storms have latitudes that are more than 6 are just that, guidelines, degrees distant from the MNGP site latitude. After and judgment is used maximization, the storm with the greatest 1-hour when storms that are rainfall depth was 22W and the storm with the potentially important for greatest 6-hour rainfall was 13W. Both of these PMP development and storms were less than 6 degrees latitude from the of the same storm type MNGP site. However, the question remains - If are still considered.

one of the storms that was farther than 6 degrees from the site had the greatest rainfaH, would that storm be considered as the UP value.*~~~~~~--;-~~~

1-1. The text should be proof read to correct instances Corrected references to Concurwlth where PlNGP is confused with MNGP such as the PlNGP. resolutions.

drainage area value on Page 10 of 68, Paragraph 5.3.11.1 on Page 43 of 68, and Table 7 listing the Corrected in 12-14-2014 UP values. revision-track changes edits have now been u dated correct! .

12. Pages 26 & 37: References to Attachments B, C, Corrected to fit Concur with and D on Pages 26 and 37 of 68 should be Attachments 1, 2, and 3. resolution.

corrected (i.e. attachments are labeled numerically, not alphabetically). Corrected in 12-14-2014 revision-track changes !

edits have now been I u dated correct! .

13. Page 32, Paragraph 5.3.5 - Last paragraph, first Track changes version Concurwlth line - Word "nine" should be deleted per track showed "nine" to be resolUtlon.

changes. deleted.

Corrected in 12-14-2014 revision-track changes edits have now been u dated correct!

14. Page 35, Paragraph 5.3.6.2 - third paragraph, line fncorporated , Concur with 6 "direction an distance" should be changed to ' resolution.

"direction and distance".

15 Page 53 of 71, Table 7. The table on the right side Incorporated. Concur with of the page has the heading of Prairie Island but resolution.

the values in the table are for Monticello. If thls table !s not deleted, it should be identified in the text and the a ro riate Pl values inserted.

YL------

Date: 3/10/2015 3/10/2015 Page 3 of 3

QF-0528 Rev.

N

-0 5 ITEM COMMENTS PREPARER'S REVIEWER'S

RESOLUTION DISPOSITION 2 Change page no. 13 to 14 N/A 3 Change page no. 13 14 4 page no. 13 14 N/A N/A 5 Change page no. 26 to 27 N/A N/A 6 Change page no. 29 to 31 N/A N/A 7 Change page no. 29 to 31 NIA 8 Change page no. 34 to 36 N/A N/A 10 Change page no. 49 to 51 N/A N/A 11 Change pages no. 10 of 68 to 12 N/A and 68 70 12 no.

15 5

5 Preparer: _ _ N/A_ _ _ _ _ _ Date: _ _

Page 1 of 1

QF0549 Calculation Signature Sheet 4 QF0547 External Design Document Suitability Review Checklist 2 QF0528 Design Review Comment Form 4 TOC (this page)

Calculation 331 Total 342

1 no. 0 Name: Dariusz Karpinski Date: /15 If is related, then a the Program Engineer (typically documented in the EC or PCR) and discard this If in the process of completing this form, one box is checked "yes", then obtain a review the Fire Protection Program Engineer (typically documented in the EC or PCR) and discard this form.

If all boxes are checked "no", then the completed form should retained the parent process (PCR, EC, etc.).

YES NO 1.

Will the proposed change modify the physical location or quantity D flammable or combustible liquids stored in tanks or contained in plant equipment (including tanks and equipment)?

or D access flammable or combustible liquids or gases?

M/arb

access D [X]

fight D [X]

Does the change prefire strategies? D [X]

access D of an Will the proposed change renovate or alter the occupancy of an area or room D such as enclosing or fencing off an area for use as storage space or establishing a personnel work station or office?

Will the proposed change mod the technical nature surveillance or D periodic test procedures fire barriers or assemblies?

Are changes proposed to any floors, ceilings or walls, including exterior D Changes floors ceilings and would integral components such as doors and (including hardware), dampers, structural steel hatches, curbs, seals.

or or D D

or D M/arb

or D combustibles include insulation, oils, retardant treated wood, flammable liquids, plastics, etc. If the change is the result new cables being added or removed and the entire length cable is or be in conduit, or the cable is metal clad, this question may be answered no. If the change is result wiring, components or being installed inside an existing panel or panel, this answered no.

any special hazards being introduced into an area or room as D hydrogen or combustible metals such as titanium?

Is an ignition source being temporarily or permanently introduced into an D area or room?

480V and above electrical devices are considered ignition sources.

combustibles or hazards being norm-::. in owner D controlled area?

Will thermal stress relieving be employed? D D

D D

systems?

Will the proposed change response plant fire D M/arb

D the proposed change temporarily or permanently remove a fire D suppression system or component service?

Is structure, system or component introduced or modified such that D its final cause interterence suppression system patterns?

Will the proposed change modify the technical nature or acceptance criteria D of surveillance or periodic test procedures for the plant's fire suppression systems or water supply equipment?

Will the proposed change alter the location or of supply, or discharge D registers or other openings intended circulation in a room or area containing smoke or fire detectors; or change the velocity, quantity or direction of air being supplied or discharged from a room or area containing fire detectors?

10.

or D 11.

D or D [ZJ or or D [ZJ M/arb

D or Will the proposed change alter the thickness acceptance criteria fire D coating/fire proofing material?

1:

Is the component(s) in Appendix J D D If component is identified, answer question YES M/arb

D D

D Residual Mode)

D Service Water System D R System D

D D Main (MSIV's)

D Suppression Pool Level D Suppression Pool Temperature (SPOTMOS)

D Reactor Vessel Level D Reactor Vessel Pressure D Alternate Shutdown System (ASDS)

D Emergency Service Water System D Control Rod Drive (P-201 B)

D Reactor Water Cleanup 1)

D 1 Power System D 1 Essential D

D D

D 1

or D M/arb

1 D

1 Will the Procedure D 1

Will the proposed change alter the installation, surveillance or test D procedures associated with the portable fuel oil transfer pump?

1 Will the proposed change or replace the radio system, including D power supply?

the proposed alter technical nature or criteria D system surveillance or test procedures?

1 the or D D

or D M/arb

If a planned addition, renovation or alteration involves a structure, system or component that is (or be) insured NEIL and the change is intended be permanent (i.e., in place over 180 days), and any the questions outlined are yes, then the project requires a NEIL

1. Is a new D Does the addition, renovation or alteration change occupancy D classification of any part of a N L insured structure?

3. Does the design change involve the addition of a new fire protection D system?

Does the change significantly add to, renovate or alter an existing NEIL D required fire detection or fire protection system? example, this does not include relocation of less than 10% of the fire detectors or suppression heads/nozzles for a single system while still maintaining code compliance.

an N L insured D D

D a D D

or or use the supply and distribution systems than emergency use?

M/arb

1 or or D D

1 Does the change add to, renovate or alter collection systems, D barriers or fire protection systems oil filled component.

If boxes are process (PCR, EC, etc.).

A review is required by a Fire Protection and/or Appendix R Safe Shutdown Subject Matter Expert (SME) to determine if the proposed change affects the Fire Protection Program. It is possible that a question answered YES on this checklist eventually results in no impact to the Program. Document the review in the parent process. Typically Fire Protection/Appendix R review is documented in the parent process e.g. PROT review PCRs, milestone reviews ECs (type and DOC ONLY).

M/arb

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Calculation Type: Preliminary Final Seismic Classification: I II NS Other Safety-Related: Yes No Other OBJECTIVE The objective of this calculation is to determine the site-specific all-season and cool-season Probable Maximum Precipitation (PMP) and Local Intense Precipitation (LIP) at the site.

DEFERRED DESIGN VERIFICATION ITEMS No. Deferred Design Verification Description DVR No.* Date None COMPUTER PROGRAM CALCULATIONS Computer Program Title SPAS Version 9.5 SCR-1700-01 Computer Program Title R Version 2.15.1 SCR-1710-01 REVIEW AND APPROVAL Prepared By Approved By Rev. Print and Sign Date DVR No.* Print and Sign Date 0 Doug Hultstrand, 08/31/2014 DVR-0011 Steve Thomas 9/11/2014 1 DVR-

Indicate Design Verification Review (DVR) number.

This calculation supersedes Calculation Number None This calculation is superseded by Calculation Number None NF-3.5-1C Page 1 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Table of Contents

1.0 Purpose and Scope

...................................................................................................................................................... 6 2.0 References .................................................................................................................................................................. 9 3.0 Summary and Conclusions ........................................................................................................................................ 10 3.1 Summary of Results............................................................................................................................................. 10 3.2 Conclusions .......................................................................................................................................................... 12 4.0 Design........................................................................................................................................................................ 13 4.1 Design Inputs ....................................................................................................................................................... 13 4.1.1 National Climatic Data Center (NCDC) Cooperative Summary of the Day and Hourly Weather Observations ................................................................................................................................................................ 13 4.1.2 Hydrometeorological Reports Storm Information ................................................................................... 13 4.1.3 US Army Corps of Engineers (USACE) Storm Studies............................................................................... 13 4.1.4 Applied Weather Associates Storm Analyses ............................................................................................ 13 4.2 Design Margins .................................................................................................................................................... 13 4.3 Acceptance Criteria ............................................................................................................................................. 13 4.4 Assumptions ........................................................................................................................................................ 14 5.0 Analysis ..................................................................................................................................................................... 15 5.1 PMP Development Background.......................................................................................................................... 15 5.2 Approach .............................................................................................................................................................. 17 5.2.1 Watershed Location and Description ........................................................................................................ 18 5.3 Probable Maximum Precipitation Calculation .................................................................................................. 19 5.3.1 PMP Storm Type and Climatology.............................................................................................................. 19 5.3.2 General Weather Patterns .......................................................................................................................... 21 5.3.3 MNGP Storm Types ..................................................................................................................................... 22 5.3.3.1 Synoptic Scale Weather Systems ................................................................................................................ 22 5.3.3.2 Mesoscale Convective Systems................................................................................................................... 23 5.3.4 Storm Identification and Storm List Development ................................................................................... 25 5.3.4.1 Storm Search Data Sources ......................................................................................................................... 26 NF-3.5-2B Page 2 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 5.3.4.2 Short Storm List Derivation ........................................................................................................................ 27 5.3.5 Storm Depth-Area-Duration Analyses and Development Using SPAS .................................................... 32 5.3.5.1 SPAS Data Collection ................................................................................................................................... 33 5.3.5.2 Mass Curve ................................................................................................................................................... 33 5.3.5.3 Hourly or Sub-Hourly Precipitation Maps ................................................................................................. 33 5.3.5.4 Depth-Area-Duration Program................................................................................................................... 34 5.3.6 Updated data sets used in this study ......................................................................................................... 34 5.3.6.1 Development of the updated dew point climatology ............................................................................... 34 5.3.6.2 HYSPLIT trajectory model .......................................................................................................................... 35 5.3.7 In-place storm maximization process........................................................................................................ 36 5.3.8 Storm transposition adjustment process .................................................................................................. 40 5.3.9 Total adjustment factor calculation and use of the storm spreadsheet .................................................. 41 5.3.9.1 Moisture maximization calculations .......................................................................................................... 42 5.3.10 Storm spreadsheet development process ................................................................................................. 43 5.3.11 Development of PMP values ....................................................................................................................... 46 5.3.11.1 Envelopment procedures and DAD development ................................................................................ 46 5.3.12 Local Intense Precipitation Analysis .......................................................................................................... 50 5.3.12.1 Local Intense Precipitation Development ............................................................................................. 51 5.3.12.1.1 Local Intense Precipitation Storm List............................................................................................... 51 5.3.12.1.2 Local Intense Precipitation Calculation Process ............................................................................... 52 5.3.12.2 Local Intense Precipitation Results........................................................................................................ 53 5.3.12.2.1 Reason for reduction from HMR 52 Local Intense Precipitation values ......................................... 54 5.3.13 Site-Specific PMP values calculated during this study ............................................................................. 55 5.3.14 Controlling storms for the Site-Specific PMP values ................................................................................ 57 5.3.14.1 Comparison of the all-season PMP against precipitation frequency estimates ................................. 58 5.3.15 Reasons for reductions of all-season PMP values versus HMR 51 .......................................................... 58 5.3.16 Recommendations for application of site-specific PMP and LIP values ................................................. 60 5.4 Meteorological Time Series Development......................................................................................................... 60 NF-3.5-2B Page 3 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 5.4.1 Data and Methods ........................................................................................................................................ 61 5.4.1.1 Hourly time series ....................................................................................................................................... 63 5.4.1.2 Temperature time series maximization .................................................................................................... 65 5.4.1.3 Creation of gridded time series datasets ................................................................................................... 66 6.0 Final Results .............................................................................................................................................................. 70 7.0 Attachments .............................................................................................................................................................. 71 Attachment 1 -All-Season Short Storm List Data" (80 pages)

Attachment 2 - Cool-Season Short Storm List Data " (37 pages)

Attachment 3 -Local Intense Precipitation Short Storm List Data" (894 pages)

Attachment 4 - 100-year Return Frequency Average Dew Point Climatology Maps Used in the Storm Maximization and Transposition Calculations (36 pages)

Attachment 5 - "Procedure for using Dew Point Temperatures for Storm Maximization and Transposition (5 pages)

Attachment 6 - Procedure for Deriving PMP Values from Storm Depth-Area-Duration Analyses" (6 pages)

Attachment 7 - Depth-Area and Depth-Duration Curves (13 pages)

List of Tables Table 1. Site-Specific All-Season Probable Maximum Precipitation ............................................................................................... 11 Table 2. Site-Specific Cool-Season Probable Maximum Precipitation ............................................................................................11 Table 3. Site-Specific Local Intense Precipitation ................................................................................................................................... 12 Table 4. All-season short storm list .............................................................................................................................................................. 29 Table 5. Cool-season short storm list ........................................................................................................................................................... 31 Table 6. Local Intense Precipitation storm list ........................................................................................................................................ 52 Table 7. Site-Specific Local Intense Precipitation ................................................................................................................................... 53 Table 8. Site-Specific All-Season Probable Maximum Precipitation compared to HMR 51 values .....................................56 Table 9. Site-Specific All-Season Probable Maximum Precipitation ............................................................................................... 56 Table 10. Site-Specific Cool-Season Probable Maximum Precipitation ......................................................................................... 57 NF-3.5-2B Page 4 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Table 11. Site-specific all-season Probable Maximum Precipitation controlling storms ....................................................... 57 Table 12. Site-specific cool-season Probable Maximum Precipitation controlling storms ................................................... 58 Table 13. Example of hourly station data for KSTC, April 1954 .......................................................................................................65 List of Figures Figure 1. Overall watershed and regional location of MNGP ............................................................................................................... 8 Figure 2. Flow chart detailing the major steps in PMP development ............................................................................................. 18 Figure 3. Surface features associated with moisture moving from the Gulf of Mexico to the upper Midwest ..............20 Figure 4. Surface fronts associated with synoptic pattern leading to heavy rainfall in the upper Midwest ..................20 Figure 5. Locations of surface fronts associated ..................................................................................................................................... 22 Figure 6. Color enhanced infrared satellite image of an MCS. Note the nearly circular structure, very cold/high clouds tops (signified by the red, black, and center white colors), and a size similar to the state of Iowa. ....................24 Figure 7. Storm search domain....................................................................................................................................................................... 26 Figure 8. All-season short storm list locations in relation to the MNGP watershed ................................................................ 30 Figure 9. Cool-season short storm list locations in relation to the MNGP watershed ............................................................. 32 Figure 10. HYSPLIT Model trajectory example ........................................................................................................................................ 36 Figure 11. July 24-hour 100-year recurrence interval dew point climatology .......................................................................... 38 Figure 12. Surface dew point 12-hour average observations used in the storm representative dew point analysis for the Duluth, MN June 2012 storm event................................................................................................................................................. 40 Figure 13. Storm spreadsheet for Fall River, KS June 2007Big Rapids, MI September 1986 transpositioned to the basin centroid .........................................................................................................................................................................................................46 Figure 14. 24-hour all-season Depth-Area curves at the MNGP basin centroid ........................................................................ 47 Figure 15. 24-hour cool-season Depth-Area curves at the MNGP basin centroid ..................................................................... 48 Figure 16. All-season Depth-Duration curves at the MNGP basin centroid .................................................................................49 Figure 17. Cool- season Depth-Duration curves at the MNGP basin centroid ............................................................................50 Figure 18. Stations used in the April 1954 meteorological time series development ............................................................. 61 Figure 19. Stations used in the April 1965 meteorological time series development ............................................................. 62 Figure 20. Stations used in the April 2001 meteorological time series development ............................................................. 63 NF-3.5-2B Page 5 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Figure 21. Example of methodology to create normalized profiles. Maximum 72-hour accumulated precipitation (green line). Mid-point of 72-hour window based on 36-hour shift from maximum 72-hour accumulation (red line). Start and end point of the 120-hour duration used in analysis (blue lines). ................................................................... 64 Figure 22. Example of plotted hourly station data for KSTC, April 1954......................................................................................65 Figure 23. Four points used for QC of the meteorological time series data................................................................................. 67 Figure 24. Maximized meteorological time series data for the northern portion of the basin ............................................68 Figure 25. Maximized meteorological time series data for overall basin centroid................................................................... 69 Figure 26. Maximized meteorological time series data at the Monticello site............................................................................69 Figure 27. Maximized meteorological time series data at the Monticello site............................................................................70

1.0 Purpose and Scope

As part of a 10 CFR 50.54(f) letter to Xcel Energy, the Nuclear Regulatory Commission (NRC) requested that Monticello Nuclear Generating Plant (MNGP) perform a reevaluation of all appropriate external flooding sources, including the effects from Local Intense Precipitation (LIP) on the site, Probable Maximum Flood (PMF) on stream and rivers, storm surges, seiches, tsunami, and dam failures.

The purpose of this calculation is to estimate the site-specific Probable Maximum Precipitation (PMP) that can occur in the 14,051-square mile watershed to the MNGP watershed (Figure 1), and the LIP PMP event that can occur directly over the MNGP site. These PMP estimates are needed to calculate the PMF and maximum flood levels during the LIP event, respectively, at the plant site. PMP values representing all-season (May through October) and cool-season (November through April-also known as snow season PMP) are explicitly determined.

The PMP and LIP evaluation utilizes the most recent data available, building on several similar studies completed by Applied Weather Associates (AWA) in the region (Reference 14, Reference 23, Reference 24, Reference 25) and providing significant improvements to the Hydrometeorological Reports (HMRs) relevant for the site (HMRs 51, 52, and 53, (Reference 1, Reference 2, Reference 3). Parameters to estimate the MNGP PMP and LIP are derived based on past extreme rainfall events that have occurred in and around the locations after appropriate adjustments and maximizations have been applied. This process explicitly takes into account the characteristics that are specific to the overall watershed and MNGP site, including the unique meteorology, climatology, and topography of the region. The implementation of the updated data, methods, and meteorological understanding provides for a reliable estimation of PMP and LIP possible given the current scientific understanding and enhances the reliability of the calculations compared to the outdated HMRs.

This calculation also provides hourly meteorological data representing the temperature, dew point, and wind speeds which would be expected to occur at the same time as the cool-season PMP. These data are needed to NF-3.5-2B Page 6 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 calculate the snowmelt that would occur during the cool-season PMP. The all-season PMP and the cool-season PMP plus snowmelt respectively address Alternatives I and III (Section 9.2.1.1, Reference 4).

This calculation is performed according to the guidelines presented in the following:

1) NUREG/CR-7046, Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America (Reference 22);

2) ANSI/ANS 2.8-1992, American National Standard for Determining Design Basis Flooding at Power Reactor Sites (Reference 4).

3) Hydrometeorological Report No. 51 (HMR 51), Probable Maximum Precipitation Estimates - United States East of the 105th Meridian (Reference 1)

4) Hydrometeorological Report No. 52 (HMR 52), Application of Probable Maximum Precipitation Estimates -

United States East of the 105th Meridian (Reference 2)

5) World Meteorological Organization, Manual for Estimation of Probable Maximum Precipitation, (Reference 28)

Revision 1 replaces several appendices with the correct appendices. Revision 1 also makes some minor editorial corrections.

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Figure 1. Overall watershed and regional location of MNGP NF-3.5-2B Page 8 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 2.0 References

1) NOAA, Probable Maximum Precipitation Estimates, United States East of the 105th Meridian Hydrometeorological Report No. 51, June 1978.

2) NOAA and NRC, Application of Probable Maximum Precipitation Estimates-United States East of the 105th Meridian Hydrometeorological Report No. 52, August 1982.

3) NOAA, Seasonal Variation of 10-Square-Mile Probable Maximum Precipitation Estimates, United States East of the 105th Meridian Hydrometeorological Report No. 53, April 1980.

4) ANS, Determining Design Basis Flooding at Power Reactor Sites, an American National Standard, ANSI/ANS-2.8-1992, 1992.

5) Corrigan, P., Fenn, D.D., Kluck, D.R., and J.L. Vogel: Probable Maximum Precipitation Estimates for California. Hydrometeorological Report No. 59, U.S. National Weather Service, National Oceanic and Atmospheric Administration, U.S. Department of Commerce, Silver Spring, MD, 392 pp., 1999.

6) USACE: Storm Rainfall in the United States, Depth-Area-Duration Data. Office of Chief of Engineers, Washington, D.C., 1936-1973.

7) Draxler, R.R. and Rolph, G.D.: HYSPLIT (HYbrid Single-Particle Lagrangian Integrated Trajectory) Model access via NOAA ARL READY Website (http://ready.arl.noaa.gov/HYSPLIT.php ). NOAA Air Resources Laboratory, Silver Spring, MD, 2010.

8) Environmental Data Service: Maximum Persisting 12-Hour, 1000mb Dew Points (°F) Monthly and of Record. Climate Atlas of the United States, Env. Sci. Srv. Adm., U.S. Dept of Commerce, Washington, D.C., pp 59-60, 1968.

9) Perica, S., Martin, D., Pavlovic, S., Roy, I., Laurent, M., Trypaluk, C., Unruh, D., Yekta, M., and G.M. Bonnin:

Precipitation-Frequency Atlas of the United States, NOAA Atlas 14, Volume 8, Version 2, NOAA, NWS, Silver Spring, Maryland. http://hdsc.nws.noaa.gov/hdsc/pfds/, 2013.

10) ESRI, ArcGIS 10.0 Service Pack 5 computer software, 2010.

11) Hansen, E.M., Schwarz, F.K., and J.T. Riedel: Probable Maximum Precipitation Estimates, Colorado River and Great Basin Drainages. Hydrometeorological Report No. 49, NWS, NOAA U.S. Department of Commerce, Silver Spring, MD, 161 pp. , 1977.

12) Hansen, E.M., Schwarz, F.K., and J.T. Riedel: Probable Maximum Precipitation- Pacific Northwest States, Columbia River (Including portion of Canada), Snake River, and Pacific Drainages. Hydrometeorological Report No. 57, NWS, NOAA, U.S. Department of Commerce, Silver Spring, MD, 353 pp. , 1994.

13) Hansen, E.M., Fenn, D.D., Schreiner, L.C., Stodt, R.W., and J.F., Miller: Probable Maximum Precipitation Estimates, United States between the Continental Divide and the 103rd Meridian, Hydrometeorological Report Number 55A, NWS, NOAA, U.S. Dept of Commerce, Silver Spring, MD, 242 pp. , 1988.

14) Hershfield, D.M.: Rainfall frequency atlas of the United States for durations from 30 minutes to 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months and return periods from 1 to 100 years, Technical Paper No. 40, U. S. Weather Bureau, Washington, D.C.,

61pp. ., 1961.

15) Kappel, W.D., Hultstrand, D.M., Tomlinson, E.M., Muhlestein, G.A., and T.P. Parzybok: Site-Specific Probable Maximum Precipitation (PMP) Study for the Quad Cities Nuclear Generating Station, Quad Cities, IA. ,

September 2012.

16) Maddox, R.A.: Mesoscale convective complexes. Bull. Amer. Meteor. Soc., 61, 1374-1387, 1980.

17) Maddox, R.A.: The structure and lifecycle of midlatitude mesoscale convective complexes. Ph.D.

dissertation, Colorado State University, 171 pp., 1981.

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1

18) NCDC. NCDC TD-3200 and TD-3206 datasets - Cooperative Summary of the Day.

19) NCDC, Heavy Precipitation Page http://www.ncdc.noaa.gov/oa/climate/severeweather/rainfall.html#maps

20) NOAA Central Library Data Imaging Project Daily weather maps, http://docs.lib.noaa.gov/rescue/dwm/data_rescue_daily_weather_maps.html

21) Parzybok, T. W., and E. M. Tomlinson: A New System for Analyzing Precipitation from Storms, Hydro Review, Vol. XXV, No. 3, 58-65 , 2006.

22) U.S. NRC, Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America, NUREG/CR-7046 PNNL-20091, November 2011.

23) Tomlinson, E.M.: Probable Maximum Precipitation Study for Michigan and Wisconsin, Electric Power Research Institute, Palo Alto, Ca, TR-101554, V1., 1993.

24) Tomlinson, E.M., Kappel W.D., Parzybok, T.W., Hultstrand, D.M., Muhlestein, G.A., and P. Sutter: Statewide Probable Maximum Precipitation (PMP) Study for the state of Nebraska, Prepared for Nebraska Dam Safety, Omaha, Nebraska, December 2008.

25) Tomlinson, E.M., Kappel, W.D., Hultstrand, D.M., Muhlestein, G.A., S. Lovisone, and T. W. Parzybok:

Statewide Probable Maximum Precipitation (PMP) Study for Ohio , March 2013.

26) US Weather Bureau: An Estimate of Flood-Producing Meteorological Conditions In The Missouri River Basin Between Garrison and Fort Randall, Hydrometeorological Report Number 22, US. Department of Commerce, Washington, DC, 56 pp. , 1946.

27) US Weather Bureau: Seasonal Variation Of The Probable Maximum Precipitation East of the 105th Meridian For Areas From 10 To 1000 Square Miles And Durations Of 6, 12, 24, and 48 Hours, Hydrometeorological Report Number 33, US. Department of Commerce, Washington, DC, 33 pp. , 1956.

28) WMO: Manual for Estimation of Probable Maximum Precipitation, Operational Hydrology Report No 1045, WMO, Geneva, 259 pp. , 2009.

29) USACE: Engineering and Design Runoff From Snowmelt, Manual No. 1110-2-1406, Washington, D.C., 100 pp. , 1998.

30) USGS: Notable Local Floods of 1942-1943, Geological Survey Water-Supply Paper 1134, United States Dept.

of the Interior , 1952.

3.0 Summary and Conclusions 3.1 Summary of Results This calculation determines the site-specific rainfall during the all-season PMP and cool-season PMP storm events in the 45,24414,051 square mile watershed to MNGP. The analysis also provides the meteorological parameters used as input to the energy budget equation (Reference 29) used to determine the amount of snowmelt. The site-specific Depth-Area-Duration (DAD )values determined in this analysis are the following: (1) the all-season PMP values from 10-square miles to 100,000-square miles from 6-hours through 72-hours (Table 1), (2) the cool-season PMP values from 10-square miles to 100,000-square miles from 6-hours through 72-hours (Table 2), and (3) the site-specific LIP values for 5-, 15-, 30-minutes, 1- and 6-hours (Table 3). The tables summarizing these three results tables are replicated in this section in Tables 1, 2 and 3 respectively.

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Table 1. Site-Specific All-Season Probable Maximum Precipitation Table 2. Site-Specific Cool-Season Probable Maximum Precipitation NF-3.5-2B Page 11 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Table 3. Site-Specific Local Intense Precipitation 3.2 Conclusions

1) The site-specific all-season PMP values determined during this calculation were generally lower than those provided in HMR 51. Reasons for the differences in computed PMP values are discussed in Section 5.3.15 of this calculation. It should be noted that much of the data, process, and decisions utilized in HMR 51 to derive their PMP values are undocumented and unknown and therefore only limited comparisons can be made.

2) The site-specific LIP values determined during this calculation were lower than the values provided in HMR

52. Reasons for the differences in computed PMP values are discussed in Section 5.3.12.2.1 of this calculation. It should be noted that much of the data, process, and decisions utilized in HMR 51 to derive their PMP values are undocumented and unknown and therefore only limited comparisons can be made.

3) The storm search and selection of storms for PMP development emphasized storms with the largest rainfall values relevant to the overall basin area size of 14,051-square miles and at durations of 1-day and 3-days that are transpositionable to the basin. Therefore, PMP results derived in this calculation should not be used for basin sizes significantly smaller than evaluated here or in areas where these storms are not transpositionable.

4) The storm search and selection of storms for LIP development emphasized storms with the largest rainfall values relevant to the MNGP site with intense rainfall over area sizes less than 500-square miles, and at durations of 1-hour. Therefore, LIP results derived in this calculation should not be used for basin sizes significantly larger than 1-square mile or in areas where these storms are not transpositionable.

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 4.0 Design 4.1 Design Inputs The following inputs are used in this calculation.

4.1.1 National Climatic Data Center (NCDC) Cooperative Summary of the Day and Hourly Weather Observations The data are published by the NCDC. Data can be obtained by contacted the NCDC or using the NCDC online data request interface at http://www.ncdc.noaa.gov/data-access/quick-links.

4.1.2 Hydrometeorological Reports Storm Information Depth-Area-Duration information in the Attachment of HMR 51, 1-hour rainfall information from HMR 52 Table 21, and sub-hourly rainfall ratios from HMR 52 Figures 36, 37, and 38 were used.

4.1.3 US Army Corps of Engineers (USACE) Storm Studies Depth-Area-Duration data from USACE storm studies sheets were used. Each of the storm studies sheets used in this analysis are included in Attachments 1, 2, and 3.

4.1.4 Applied Weather Associates Storm Analyses Storm analyses completed using AWA's Storm Precipitation Analysis System (SPAS) (Reference 21) which were used in previous PMP and LIP calculations were utilized in this analysis. Data for each SPAS analysis used in this calculation are included in Attachments 1, 2, and 3. Each SPAS analysis used in this calculation has been peer reviewed during the development of PMP and LIP values during other calculations. All SPAS analyses have been accepted for use in PMP and LIP determination by the Federal Energy Regulatory Commission (FERC)..

4.2 Design Margins Client Margin - No specific margin is required by the client.

Safety Margin - No specific safety margin is applied.

Design Margin - No specific design margin is applied.

Operation Margin - No specific operation margin is applied.

Other Margin - No specific other margins are applied.

4.3 Acceptance Criteria There are no acceptance criteria associated with this calculation. This calculation only determines input values for use in subsequent analyses.

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 4.4 Assumptions There are no unverified assumptions used in this calculation.

The following verified assumptions are used in this calculation.

1) This calculation assumes that if we an appropriate set ofThe storm events has been identified, analyzed, and maximized, they will represent the meteorological environment associated with the PMP for the basin and the LIP for the site. This assumption is validated by including a large enough set of PMP-type and LIP-type storms to ensure no storms which could have potentially affected PMP or LIP values after all adjustments were applied were left out of the analysis. This same assumption is made in HMR 51 (Reference 1).

2) It is assumed that storms transposed to the MNGP basin centroid for PMP or the MNGP site location for LIP could have occurred over the area under similar meteorological conditions. This decision is made using scientific judgment related to the storm type, season of occurrence, similarity of topography between the original locations and the new location, and experience analyzing past storms. Parameters used in screening for transpositionability include not moving storms across the Appalachian crest, employing a +/-

1,000 foot limitation between the original storm location and the basin centroid or site location, and limiting the north/south region of transposition to approximately +/- 6° longitude. Note that judgment is still employed for storms that are questionable following these guidelines so that conservatism is applied when a storm potentially affecting PMP is near one of these boundaries. This follows the same guidance provided in HMR 51 Section 2.4.2 (Reference 1).

3) It is assumed that the cool-season PMP values are considered and analyzed as a rain-on-snow scenario where some amount of rainfall accumulates when snow is on the ground and are combined with a given amount of snow melt to derive the total runoff associated with a cool-season PMP The cool-season PMP values are considered and analyzed as a rain-on-snow scenario and are combined with a given amount of snow melt to derive the total runoff associated with a cool-season PMP rainfall.

4) The atmospheric air masses that provide moisture to both historic storms and the PMP storm are assumed to be saturated through the entire depth of the atmosphere and to contain the maximum moisture possible based on the surface dew point. This assumes moist pseudo-adiabatic temperature profiles for both the historic storms and the PMP storm. In addition, it is assumed that the maximum amount of moisture the atmosphere can hold is available to the PMP storm. This follows the same guidance provided in HMR 51 (Reference 1) and WMO Manual for PMP (Reference 28).

5) The assumption is made that if additional atmospheric moisture had been available, the storm would have maintained the same efficiency for converting atmospheric moisture to rainfall. The ratio of the maximized rainfall amounts to the actual rainfall amounts would be the same as the ratio of the precipitable water (the total atmospheric water vapor contained in a vertical column of unit cross-sectional area extending between any two specified levels in the atmosphere) in the atmosphere associated with each storm. For this analysis, the assumption of no change in storm efficiency is accepted, mirroring the HMR (Reference 1) and WMO assumptions (Reference 28).

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1

6) The climatological maximum dew point for a date 15 days towards the warm season from the date that the storm actually occurred is applied in the storm maximization process. This procedure assumes that the storm could have occurred 15 days earlier or later in the year when maximum dew points (and moisture levels) are higher. This assumption follows HMR guidance and is consistent with procedures used to develop PMP values in all the current HMR documents (e.g., HMR 51, Section 2.3 Reference 1; HMR 59, Section 4.2, Reference 5; and World Meteorological Organization (WMO) (Reference 28), as well as all AWA PMP studies (Reference 15, Reference 23, Reference 24, Reference 25).

7) Storm efficiency does not change if additional atmospheric moisture is available. For this analysis, the assumption of no change in storm efficiency is accepted, mirroring the HMR (Reference 1) and WMO assumptions (Reference 28).

8)7) Changes in climate that will occur in the region are adequately accounted for by the rarity of the resulting PMP and LIP values. Further, changes in climate which have occurred during the past 150 years are captured in the storm record and rainfall data used in this analysis and therefore represent any changes that would be expected during the useful lifetime of the values. Therefore, no adjustment is made to account for potential changes in climate. This follows the same guidance provided in the HMRs (Reference

1) and WMO Manual for PMP of assuming no climate change (Reference 28).

5.0 Analysis This calculation provides both all-season and cool-season PMP values for use in the computation of the Probable Maximum Flood (PMF) for the MNGP watershed and the LIP values for the MNGP site. The site-specific calculations build on the previous PMP studies completed by AWA in the region (e.g., Reference 15, Reference 23, Reference 24, Reference 25).

The PMP is a deterministic estimate of the theoretical maximum depth of precipitation that can occur over a specified area. Parameters to estimate the PMP were developed based on the storm based, deterministic approach as presented in HMR 51 and subsequently refined in the numerous site-specific, statewide, and regional PMP studies completed since its publication in 1978. All-season PMP, cool-season PMP, and LIP were calculated following the storm based approach and provide deterministic values for each.

5.1 PMP Development Background Definitions of PMP are found in most HMRs published by the National Weather Service (NWS). The definition used in the most recently published HMR (HMR 59, p. 5 Reference 5) is "theoretically, the greatest depth of precipitation for a given duration that is physically possible over a given storm area at a particular geographical location at a certain time of the year." From the mid-1940s through the mid-1990's, several government agencies had been developing methods to calculate PMP in various regions of the United States. The NWS (formerly the U.S. Weather Bureau) and the Bureau of Reclamation had been the primary agencies involved in this activity. PMP values from their reports are used to calculate the PMF which, in turn, is often used for the design of significant hydraulic structures and in this case to determine flood protection actions.

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 The generalized PMP studies currently in use in the conterminous United States include HMR 49 (Reference 11) for the Colorado River and Great Basin drainage; HMRs 51 (Reference 1), 52 (Reference 2) and 53 (Reference 3) for the U.S. east of the 105th meridian; HMR 55A (13) for the area between the Continental Divide and the 103rd meridian; HMR 57 (12) for the Columbia River Drainage; and HMR 59 (5) for California. The region covered by HMR 51 constitutes the largest generalized region addressed by a single HMR. In addition to these HMRs, numerous Technical Papers and Reports deal with specific subjects concerning precipitation. Topics include maximum observed rainfall amounts, return periods for various rainfall amounts, and specific storm studies.

Climatological atlases are available for use in determining rainfall amounts for specified return periods for selected regions of the U.S.

However, there are no concurrent HMR documents providing cool-season PMP values. In addition, very little documentation related to cool-season PMF scenarios and meteorological guidance exists. The USACE (1973, 1998) and American Nuclear Society (ANS,1992) have published documents with guidance related to snow accumulation and snow melt and use with rain-on-snow runoff situations. However, most of the data associated with cool-season PMF is outdated (e.g. HMR 22 US Weather Bureau 1946, Reference 26). Therefore, it was imperative that as part of this PMP calculation, the cool-season PMP was explicitly derived. In addition, the meteorological parameters used to model snowmelt that would occur during the cool-season PMP required extensive analyses using the same storm based approach to ensure consistency of such parameters from the proper modeling and development of the cool-season PMF.

A number of site-specific and regional PMP studies augment generalized HMRs. These studies are for specific regions or drainage basins within the large area addressed by HMR 51 (over half of the contiguous United States).

The meteorological conditions producing extreme rainfall events vary significantly in different regions within this large geographic area. In much of the Midwest and the regional affecting the MNGP watershed, extreme events are usually linked to either Mesoscale Convective Systems (MCSs) or synoptic storms with embedded convection. The main storm type leading to PMF level flooding is a synoptic event with embedded convection. This type of storm provides steady rainfall over long durations and large area sizes, with periods of heavy rainfall. This same type of storm occurs in the spring, but with less moisture available. However, when antecedent snow pack is on the ground, the combination of rain-on-snow may overcome the limited moisture for rainfall production to produce PMF level floods. Because short duration, intense rainfalls produced by MCS storms do not produce large flood events for this basin, this storm type was excluded from the PMP analysis and therefore did not influence the all-season PMP values. This storm type was explicitly accounted for in the development of the LIP values (see Section 5.3.12). Not including this storm type for basin-wide PMP development only affects area sizes less than 500-square miles and durations less than 24-hours.

Although it provides generalized estimates of PMP values for a large, climatologically diverse area, HMR 51 recognizes that studies addressing PMP over specific regions can incorporate more site-specific considerations and provide improved PMP estimates. By periodically reviewing storm data and advances in meteorological concepts, PMP analysts can identify relevant new data and approaches for use in determining PMP estimates (HMR 51, Section 1.4.1).

As described previously, several site-specific, statewide, and regional PMP studies have been completed by AWA (e.g. Reference 15, Reference 23, Reference 24, Reference 25) within the region covered by HMR 51. Each of these studies provided PMP values which replaced those from HMR 51. In addition, in regions where rain-on-snow NF-3.5-2B Page 16 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 scenarios could potentially produce the PMF, a cool-season analysis was also completed (e.g. Reference 15). These are good examples of PMP studies that explicitly consider the meteorology and topography of the study location along with characteristics of historic extreme storms over climatically similar regions. Information, experience, and data derived during these previous AWA PMP studies were utilized in this calculation. This included use of the previously analyzed storm events using the Storm Precipitation Analysis System (SPAS) program, the previously derived storm lists, the previously derived storm maximizations and climatologies, and the explicit understanding of the meteorology of the region. In addition, comparisons to these previous studies provided sensitivity and context against the results of this calculation. These regional and site-specific PMP studies have received extensive review and been accepted by the appropriate regulatory agencies, including the Federal Energy Regulatory Commission, state dam safety regulators, the Natural Resources Conservation Service (NRCS), the USACE, and the Bureau of Reclamation (USBR). Results have been used in computing the PMF for individual watersheds.

5.2 Approach The approach used in this calculation follows the same basic procedures that were used in the development of the HMRs and as recommended in the WMO Manual for PMP. These procedures were applied considering the meteorological and topographic characteristics of the basin. The calculation maintains as much consistency as possible with the general method used in HMR 51 and the numerous site-specific, statewide, and regional PMP studies AWA has completed. Deviations are incorporated where justified by developments in meteorological analyses and available data. The basic approach identifies PMP-type storms that occurred within the central United States and southern Canada west of the first upslope of the west side of the Appalachians to approximately 100° longitude and south to the southern plains. This ensured a sufficiently large region was included in the storm list development so that any transpositionable storm that could potentially affect the all-season or cool-season PMP values at any area size or duration was included.

The moisture content of each of these storms is maximized to provide an estimate of the maximum rainfall for each storm at the location where it occurred. This is accomplished by computing the ratio of the maximum amount of atmospheric moisture that could have been entrained into the storm at that time of year to the actual atmospheric moisture entrained into the storm as it occurred in-place. After maximization, the storms are transpositioned to the basin centroid to the extent supportable by similarity of meteorological conditions and topography. Maximized and transpositioned adjusted rainfall values are enveloped at the basin centroid to provide PMP estimates for various area sizes and durations. Figure 2 shows the flow chart of the major steps in the PMP development process. There are a number of assumptions that need to be applied to establish a consistent application of meteorological principles. These assumptions are provided in Section 4.4.

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Figure 2. Flow chart detailing the major steps in PMP development 5.2.1 Watershed Location and Description The MNGP watershed covers most of the central Minnesota (see Figure 1). The northerly latitude of the basin's location in the Upper Midwest plays an important role in the PMP storm types and the cool-season PMP/PMF scenarios. Often, a snow pack accumulates during the winter season and is available to melt in conjunction with spring rainfall. The large size of the basin and its geographic location have been explicitly evaluated and considered during the calculation to ensure appropriate PMP development. Elevation changes across the basin are not extreme and range from just over 800 feet at the MNGP site along the Mississippi River to over 1,896 feet in northwestern area of the watershed. Therefore, no elevation limitations are placed on storms within the basin, and instead the average basin elevation and basin centroid location are used in all storm maximization and transposition calculations.

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 5.3 Probable Maximum Precipitation Calculation The all-season and cool-season PMP calculations, as well as the LIP, were completed using Microsoft Excel spreadsheets, SPAS and ESRI ArcGIS. The current state-of-the-science meteorological methodologies were employed as described below in identifying, maximization, and combining storms to produce PMP and LIP values.

The deterministic, storm-based approach as described in the HMRs and follow in all previous AWA studies was utilized as the basic methodology during the calculation.

5.3.1 PMP Storm Type and Climatology The region around the MNGP watershed is influenced by several factors that can potentially contribute to extreme rainfall. First is the proximity of the region to the Gulf of Mexico and the fact that no intervening barrier prevents moisture from moving north (Figure 3). This allows elevated amounts of moisture to move directly into the region. The limiting factor is the duration that these high levels of moisture are able to feed into storms in the region. Because of the basin's northerly locations and distance from the Gulf of Mexico, storm patterns generally do not stay fixed in one location for long periods. Therefore, the synoptic situations which lead to high levels of Gulf moisture moving into the region are transient and limit the magnitude of PMP-type rainfall as well as limiting the spatial extent of such storms. This lack of consistent moisture is somewhat compensated for by the stronger storm dynamics associated with synoptic weather systems which move through the region.

In addition to the moisture, a mechanism is required to produce rising motions in the atmosphere and condense the moisture. The lift required to convert these high levels of atmospheric moisture into rainfall on the ground is provided in several ways in and around the region. Synoptic storm dynamics are very effective in converting atmospheric moisture into rainfall on the ground. These are most often associated with fronts which affect the region (Figure 4). Numerous large scale weather systems with their associated fronts traverse the northern Great Plains and upper Midwest through the year, with the fewest and weakest occurring in the summer period. The fronts (boundaries between two different air masses) can be a focusing mechanism providing upward motion in the atmosphere. These are often locations where heavy rainfall is produced. Normally a front will move through with enough speed that no one area receives excessive amounts of rainfall. However, in extreme instances the pattern can become blocked and some of these fronts will stall or move very slowly across the region. This allows heavy amounts of rainfall to continue for several days in the same general area, which can lead to extreme widespread flooding.

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Figure 3. Surface features associated with moisture moving from the Gulf of Mexico to the upper Midwest Figure 4. Surface fronts associated with synoptic pattern leading to heavy rainfall in the upper Midwest NF-3.5-2B Page 20 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Another mechanism which creates lift in the region is heating of the surface and lower atmosphere by the solar radiation. This creates warmer air below colder air resulting in atmospheric instability and leads to rising motions.

This will often form ordinary afternoon and evening thunderstorms. However, in unique circumstances the instability and moisture levels in the atmosphere can reach very high levels and stay over the same region for an extended period of time. This can lead to intense thunderstorms and very heavy rainfall. If these storms are focused over the same area for a long period, flooding rains can be produced. This type of storm produces some of the largest point rainfall amounts recorded, but often do not affect larger areas with extreme rainfall amounts.

Therefore, although this rainfall producing mechanism is common in the spring and summer, they do not lead to PMF level flood events across the very large MNGP watershed. However, this is the type of storm which could produce the LIP rainfall over the MNGP site.

5.3.2 General Weather Patterns The weather patterns in the region are characterized by passages of fronts with differing air masses that lead to large ranges in temperatures and rainfall. Fronts are most prevalent in the fall, winter, and spring, with more stagnant patterns common from late spring through early fall (see Figure 5).

There are several air mass types that affect the weather and climate of the region and produce heavy rainfall. The continental polar (cP) air mass, with origins from the arctic regions of Canada, is most common during the winter months. This air mass is often associated with a strong cold front passage and stratiform snowfall events. When this air mass type arrives, it often collides with a more humid air mass from warmer regions to the south. Low pressure (rising air) often results, and when combined with strong winds aloft, can produce flooding. This is also a common storm type for cool-season rainfall events, occurring most often from March through April.

The second type of air mass observed in the region is the maritime polar (mP) which originates in the Gulf of Alaska and Pacific Ocean. This air mass often arrives on strong winds from the west and northwest, but is usually devoid of significant amounts of low level moisture because it has traveled across several mountain ranges. This storm type often produces precipitation (rain and snow) at these upstream locations, losing much of its low-level moisture on its way to the northern and central Plains. However, in extreme cases, moisture flowing north from the Gulf of Mexico can replenish low-level atmospheric moisture enough to produce heavy rainfall. If the storm system stalls over the region, flood producing rains can result. This storm type can occur anytime of the year, but is most common from fall through late spring. This scenario can produce heavy rain-on-snow during the cool-season PMP scenario.

Another type of air mass which affects the region and produces rainfall originates from the Gulf of Mexico and can contain copious amounts of atmospheric moisture in a conditionally unstable atmosphere. This type of air mass is called maritime tropical (mT). This type of air mass is most directly responsible for producing heavy rainfall in the region when interacting with a front and as well as an air mass of polar origins moving from the north. Generally, the frontal boundary is located just to the south or within the southern portions of the basin, allowing high amounts of moisture to stream in from the south and is lifted over the frontal boundary. The release of the conditional instability in the atmosphere provides a very efficient mechanism to convert atmospheric moisture to rain on the ground. If this pattern is able to remain in place for an extended period and continue to tap into Gulf of Mexico moisture, flooding can result. This storm type is most common in the summer to early fall and is therefore the most common storm type for the all-season PMP scenario.

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Figure 5. Locations of surface fronts associated 5.3.3 MNGP Storm Types The MNGP watershed and the surrounding region have very active and varied weather patterns throughout the year. Consequently heavy rainfall events at both short and long durations are common. By far, the largest amount of moisture available for rainfall over the region comes from the Gulf of Mexico. The major types of extreme rainfall events in the region are produced by Mesoscale Convective Systems (MCS's), which produce high rainfalls at short durations and small area sizes and synoptic events/fronts, which produce rainfall over large areas sizes and longer durations.

5.3.3.1 Synoptic Scale Weather Systems The polar front and jet stream, which separate cool, dry Canadian air to the north from warm, moist air to the south, is often a cause of heavy rainfall over large areas and long durations. This boundary provides large amounts of energy and strong storm dynamics to the atmosphere as fronts move through the region. These features are NF-3.5-2B Page 22 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 strongest and most active over the area during fall, winter, and spring months. A common type of storm occurrence with the polar front is an overrunning event. Frontal overrunning occurs when warm, humid air carried northward around the western edge of the Bermuda High circulation encounters the frontal zone and is forced to rise over the cooler, drier air mass to the north of the front. This forced ascent condenses atmospheric moisture in the air mass, forming clouds and producing precipitation while releasing latent heat. This process most often results in widespread rainfall over longer durations, but can also help enhance convection. Air that arrives at the frontal location is conditionally unstable, where the lower layers are much warmer and more humid than the air above. This conditionally unstable air mass needs a mechanism to initiate lift to begin energy release, leading to more instability and further lift. The forced ascent over the polar front initiates the lifting of the moist air mass, release of its energy in the form of latent heat, and initiates the conversion of the atmospheric moisture to rainfall.

A stationary or slow moving polar front located near the MNGP watershed will often provide the mechanism necessary for this warm, humid air mass to release its convective potential. When this occurs, rainfall is produced, sometimes associated with pockets of convection and extremely heavy rainfall. The pockets of heavy rain are usually associated with a minor wave riding along the frontal boundary, called a shortwave. These are not strong enough to move the overall large scale pattern, but instead add to the storm dynamics and energy available for producing rainfall.

This type of storm environment (synoptic frontal) will usually not produce the highest rainfall rates over short durations, but instead leads to flooding situations as heavy to moderate rain continues to fall over the same regions for an extended period of time. In addition, this scenario can occur during the cool-season and therefore enhance snow melt runoff with an intense rain-on-snow even.

5.3.3.2 Mesoscale Convective Systems Mesoscale Convective Systems (MCS, Reference 16, Reference 17) are capable of producing extreme amounts of rainfall for short durations and over small area sizes, generally 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months or less over area sizes of 500-square miles or less. The current understanding of MCS type storms has progressed tremendously with the advent of satellite technology starting in the 1970s and early 1980s. The current name of MCS was first applied in the late 1970s to these type of flood producing, strong thunderstorm complexes (Maddox 1980, Maddox 1981). Mesoscale systems are so named because they are small in areal extent (10's to 100's of square miles), whereas synoptic storm events are 100's to 1000's of square miles. MCSs also exhibit a distinctive signature on satellite imagery where they show rapidly growing cirrus clouds shields with very high cloud tops. Furthermore, the high level cloud shield associated with MCSs usually take on a nearly circular pattern about the size of the state of Iowa with constantly regenerating thunderstorms fed by a low-level-jet (LLJ) bringing an inflow of atmospheric moisture (Figure 6).

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Figure 6. Color enhanced infrared satellite image of an MCS. Note the nearly circular structure, very cold/high clouds tops (signified by the red, black, and center white colors), and a size similar to the state of Iowa.

MCSs are included in the more general definition of Mesoscale Convective Complexes (MCCs), which include a wider variety of mesoscale sized storm systems, such as squall lines and tropical cyclones, and MCSs that do not fit the strict definition of size, duration, and/or appearance on satellite imagery. MCSs primarily form during the warm season months (May through October) around the MNGP region.

Many of the storms previously analyzed by the USACE and NWS Hydrometeorological Branch in support of pre-1979 PMP research have features that indicate they were most likely MCCs or MCSs. However, this nomenclature had not yet been introduced into the scientific literature, nor were the events fully understood. For MNGP watershed, pure MCS storms do not produce PMF level flood events because of the very large basin size and the relatively small areas of rainfall produced by MCSs. However, intense convection similar to this storm type can occur within an overall synoptic frontal event. This can lead to intense areas of embedded rainfall within the NF-3.5-2B Page 24 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 overall lighter rainfall pattern. This combination of synoptic and convective storm types is very important for determining PMP values for the basin. Most importantly, these types of storms, along with individual thunderstorms, produce the LIP rainfall at the MNGP site.

5.3.4 Storm Identification and Storm List Development A comprehensive storm search covering the region important for the MNGP watershed has been conducted during previous site-specific and regional PMP studies. This included an analysis of all extreme rainfall storms in meteorological and topographically similar regions, where extreme rainfall storms similar to those that could occur over some part of the basin may have been observed. These previous storm search results are current through mid-2014 and include all 12 months of the year, and therefore allowed for storm list development for both the all-season and cool-season storm lists (Figure 7). This insured a large enough area was analyzed to capture all significant storms that could potentially influence the final PMP values for the basin.

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Figure 7. Storm search domain 5.3.4.1 Storm Search Data Sources Storm searches and storm list development were completed by analyzing the storm lists used in the PMP studies completed by the NWS and AWA in the region within the storm search domain. All storms used in previous studies were equal to or greater than the 100-year recurrence interval value associated with the total storm accumulation at the storm center location. This ensures that only storms which could potentially influence PMP values were further analyzed. In addition, each of the storms used in the previous PMP analyses were important for PMP development after all adjustment calculations were applied. Storms used in PMP development during those studies were compiled into a long list of storms for this work. Each of these storms were verified for use in PMP NF-3.5-2B Page 26 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 and LIP development as being accurate analyses of the given event. Numerous data sets and resources were used in the storm search and storm validation process during these previous studies. These include the NCDC, HMRs, USACE Storm Studies, United States Geological Survey reports, peer reviewed journal articles, Community Collaborative Rain, Hail, and Snow network (COCORAHS), NWS office reports, various weather books, and other publications. All of these data and the resulting storm events have been accepted through thorough peer review processes which included independent expert review and Federal and state dame safety acceptance.

5.3.4.2 Short Storm List Derivation The final short storm list used to determine the PMP values for MNGP watershed was derived using the results of previous PMP studies in regions similar to this basin. These include the EPRI Michigan/Wisconsin Regional PMP study, the Nebraska Statewide PMP study, the Ohio Statewide PMP study, the Wyoming Statewide PMP study, the Tarrant Regional Water District PMP study, and the Quad Cities PMP study.

During this process, the final short storm lists used in each of these studies was combined and evaluated. The first set of parameters used to delineate the storms was whether they were transpositionable to the basin centroid.

Factors such as elevation differences of more than +/- 1,000 feet and/or distances of more than +/- six degrees6° latitude were considered. These factors follow guidance in the HMRs (Reference 1, Reference 12, Reference 13). A few storms with storm centers in the southern Great Plains and Midwest were included even though they were slightly more than 6° latitude difference than the basin centroid latitude. This is because these storms are of the same type that would be expected over the basin and could produce PMP and they had rainfall accumulations which extended well north of the highest rainfall center location and therefore within the 6° latitude extent. In these situations, the conservative assumption is employed and the storm is allowed to be used in the PMP calculations. This applied to both cool-season and all-season storm transposition considerations. Finally, the storm type was evaluated. Storm types which would not result in a PMP/PMF scenario for the large MNGP watershed were not considered. This included storms which were individual MCS and thunderstorms.

Three storms used in the all-season PMP development of the Prairie Island Nuclear Generating Plant (PINGP) were not used in the PMP development for MNGP. This is because these three storms occurred furhter south than the storm used here and well south of the 6° latitude consideration. This combined with the fact that the majority of the MNGP basin is farther north than the Prairie Island Nuclear Generating Plant PINGP) meant that these storms were not used in the PMP development at MNGP. Next, the storm type was evaluated. Storm types which would not result in a PMP/PMF scenario for the large MNGP watershed were not considered. This included storms which were individual MCS and thunderstorms.

These analyses resulted in the final short storm lists used to derive both the all-season and cool-season PMP values for the basin. Tables 4 and 5 display the storm lists. Figures 8 and 9 display the locations of the storms on each list. The AWA Storm Number is used to identify each storm used in this calculation to derive PMP values, with the "W" designation representing the all-season storm period and the "C" representing the cool-season storm period.

Note that the locator shown on the Figures 8 and 9 represents the location with the highest recorded total storm rainfall for each event. However, the overall rainfall pattern is generally much larger, often covering thousands of square miles. The total storm rainfall patterns for each storm, along with other relevant storm information, can be found in Attachments B1, C 2 and D3.

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Many of the storms included in the final short storm list used to calculate PMP values occurred many hundreds of miles away from the MNGP watershed. Storm centers were used from locations as far north as southern Canada and as far as south as southern Missouri. This is required because it is unlikely that a storm has occurred over the basin being studied which controls PMP values at all area sizes and durations during the period of record for which data is available. Therefore, by including a large area from which to transposition storm events, one is trading space for time. And, as long as all the storms being moved in from these distant locations are considered transpositionable (similar topography and meteorology between the two locations), then standard procedures are being followed.

For cool-season storms, an additional consideration was applied to the storms used and whether they were considered transpositionable. In those scenarios, the storm dynamics (which provided the lift and turn moisture in the air to rainfall on the ground) had to be similar to what would have been expected to occur over the MNGP watershed during rain-on-snow events. Therefore, all the storms on the cool-season short storm list are of the general storm type where a slow moving (or stalled) front separating cold air to the north and west and warm air to the south and east is located over the Midwest. This synoptic situation is common in the winter and spring over the region, with storms in the historical record having occurred from southern Canada to the southern plains.

These storms generally produce widespread rainfall over several days, often with embedded convection. In some instances, especially ones which have occurred over the more northern latitudes, snow is on the ground when the rain falls, while in other situations there is no snow on the ground. However, whether snow is on the ground or not during the actual storm occurrence was not a deciding factor in whether to include a given event in the analysis.

Instead, the storm had to be able to occur hypothetically over the MNGP watershed (be transpositionable) in a situation when snow could have been on the ground and be of the appropriate synoptic storm type to be a storm which could occur with snow on the ground whether there was any during the actual storm or not. This is similar to the assumptions of using past extreme rainfall events and assuming they represent what a PMP storm would look like after maximization and transposition and is fundamental to the storm-based deterministic procedures..

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Table 4. All-season short storm list NF-3.5-2B Page 29 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Figure 8. All-season short storm list locations in relation to the MNGP watershed NF-3.5-2B Page 30 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Table 5. Cool-season short storm list NF-3.5-2B Page 31 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Figure 9. Cool-season short storm list locations in relation to the MNGP watershed 5.3.5 Storm Depth-Area-Duration Analyses and Development Using SPAS For newly identified extreme rainfall events without published DAD analyses, full storm analyses needed to be completed. SPAS was used to compute DADs for these storms.

The DAD analysis is completed by creation of high-resolution hourly precipitation grids and computation of depth-area rainfall amounts for various durations. Reliability of results depends on the accuracy of hourly rainfall grids.

SPAS utilizes Geographic Information Systems (GIS) concepts to create more spatially-oriented and accurate results in an efficient manner (step 1). Furthermore, the availability of NEXRAD data allows SPAS to better account NF-3.5-2B Page 32 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 for the spatial and temporal variability of storm precipitation for events occurring since the early 1990s. Prior to NEXRAD, the National Weather Service (NWS) developed and used a method based on the research of several scientists (Reference 6). Because this process has been the standard for many years and holds merit, the DAD analysis process developed within the SPAS program attempts to mimic it as much as possible. By adopting this approach, consistency between the newly analyzed storms and the hundreds of storms already analyzed is achieved.

As part of the development of the PMP values for the MNGP basin, nine 12 SPAS storms were used, nine all-season storms and three cool-season storms. The results of each SPAS storm analysis are included in Attachments 1, 2, and 3.

5.3.5.1 SPAS Data Collection The areal extent of a storms rainfall was evaluated using existing maps and documents along with plots of total storm rainfall. Based on the storms spatial domain (longitude-latitude box), hourly and daily data were extracted for the specified area, date and time. To account for the temporal variability in observation times at daily stations, the extracted hourly data must capture the entire observational period of all extracted daily stations. For example, if a station takes daily observations at 8:00 AM local time, then the hourly data needs to be complete from 8:00 AM local time the day prior. As long as the hourly data are sufficient to capture all of the daily station observations, the hourly variability in the daily observations can be properly addressed.

The daily database is comprised of data from NCDC TD-3206 (pre 1948) and TD-3200 (1948 through present).

The hourly database is comprised of data from NCDC TD-3240 and NOAAs Meteorological Assimilation Data Ingest System (MADIS). The daily supplemental database is largely comprised of data from bucket surveys, local rain gauge networks (e.g. ALERT, USGS) and daily gauges with accumulated data.

5.3.5.2 Mass Curve The most complete rainfall observational dataset available is compiled for each storm. To obtain temporal resolution to the nearest hour in the final DAD results, it is necessary to distribute the daily precipitation observations (at daily stations) into hourly bins. This process has traditionally been accomplished by anchoring each of the daily stations to a single hourly timer station. However, this may introduce biases and may not correctly represent hourly precipitation at locations between hourly stations. A preferred approach is to anchor the daily station to some set of the nearest hourly stations. This is accomplished using a spatially based approach that is called the spatially based mass curve (SMC) process.

5.3.5.3 Hourly or Sub-Hourly Precipitation Maps At this point, SPAS can either operate in its standard mode or in NEXRAD-mode to create high resolution hourly or sub-hourly (for NEXRAD storms) grids. In practice both modes are run when NEXRAD data are available so that a comparison can be made between the methods. Regardless of the mode, the resulting rainfall grids serve as the basis for the DAD computations.

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 5.3.5.4 Depth-Area-Duration Program The DAD extension of SPAS runs from within a Geographic Resource Analysis Support System (GRASS) GIS environment and utilizes many of the built-in functions for calculation of area sizes and average depths. The following is an outline of the procedure:

1) Given a duration (e.g. x-hours) and cumulative precipitation, sum up the appropriate hourly or sub-hourly precipitation grids to obtain an x-hour total precipitation grid starting with the first x-hour moving window.

2) Determine x-hour precipitation total and its associated areal coverage. Store these values. Repeat for various lower rainfall thresholds. Store the average rainfall depths and area sizes.

3) The result is a table of depth of precipitation and associated area sizes for each x-hour window location.

Summarize the results by moving through each of the area sizes and choosing the maximum precipitation amount. A log-linear plot of these values provides the depth-area curve for the x-hour duration.

4) Based on the log-linear plot of the rainfall depth-area curve for the x-hour duration, determine rainfall amounts for the standard area sizes for the final DAD table. Store these values as the rainfall amounts for the standard sizes for the x-duration period. Determine if the x-hour duration period is the longest duration period being analyzed. If it is not, analyze the next longest duration period and return to step 1.

Construct the final DAD table with the stored rainfall values for each standard area for each duration period most.

5.3.6 Updated data sets used in this study Updated data sets not used in the development of HMR 51 were used as part of this calculation in the development of the PMP values. These include the derivation of an updated maximum dew point climatology for use in storm maximization and transposition, the use of the Hybrid Single Particle Lagrangian Integrated Trajectory Model trajectory model (HYSPLIT) (Reference 7) to help in identifying the moisture source region for individual storm events, and the new SPAS storm analyses discussed previously. The identification and use of these data sets provide a significant improvement in storm adjustments, especially relating to the determination of each storms moisture source and derivation of appropriate maximization factor.

5.3.6.1 Development of the updated dew point climatology As part of previous and ongoing AWA PMP studies, updated dew point climatologies have been developed. These updated maximum average dew point climatologies provide 20-year, 50-year, and 100-year return frequency values for 6-hour, 12-hour, and 24-hour durations. This process followed the same reasoning and use as described in the other AWA PMP studies (Reference 15, Reference, 23, Reference 24). These analyses demonstrated that the maximum 12-hour persisting dew point climatology used in HMR 51 was outdated and more importantly did not adequately represent the atmospheric moisture available in the PMP storm environment. The updated climatology more accurately represents the atmospheric moisture fueling storms by using average maximum dew point values observed over durations specific to each storms rainfall duration. The average maximum dew point values replace the maximum 12-hour persisting dew point values which often missed or underestimated the atmospheric moisture available and hence lead to overly conservative maximization calculations.

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 5.3.6.2 HYSPLIT trajectory model The HYSPLIT trajectory model developed by the NOAA Air Resources Laboratory (Reference 7) was used during the analysis of each of the rainfall events included on the short storm list when available 1948-present from the National Centers for Environmental Prediction (NCEP) Global Reanalysis fields. Use of a trajectory model provides increased confidence for determining moisture inflow vectors and storm representative dew points. The HYSPLIT model trajectories have been used to analyze the moisture inflow vectors in other PMP studies completed by AWA over the past several years. During these analyses, the model trajectory results were verified and the utility explicitly evaluated.

Instead of subjectively determining the moisture inflow trajectory using hand analysis of weather observations, the HYSPLIT model web interface was used to determine the trajectory of the moisture inflow, both location and altitude, for various levels in the atmosphere associated with the storms rainfall production. The HYSPLIT model was run for trajectories at several levels of the lower atmosphere to capture the moisture source for each storm event. These included 700mb (approximately 10,000 feet), 850mb (approximately 5,000 feet), and storm center location surface elevation. For the majority of the analyses a combination of all three levels was determined to be most appropriate for use in evaluation of the upwind moisture source location. It is important to note that the resulting HYSPLIT model trajectories are only used as a general guide of where to evaluate the moisture source for storms in space and time. The final determination of the storm representative dew point and its location is determined following the standard procedures used by AWA in previous PMP studies and as outlined in the HMRs and WMO manuals. As an example, Figure 10 shows the HYSPLIT trajectory model results used to analyze the inflow vector for the Ashland, WI, April 2001.

In this example, all three levels of the HYSPLIT trajectory analysis show air parcels (and hence moisture) advecting into the storm center from a southerly component. This information is then used with other data sources such as surface dew point observations, synoptic weather patterns, and moisture source regions to help identify regions for evaluation of the moisture source and storm representative dew point used in the storm maximization process.

The point selected as the storm representative dew point location is then connected to the storm center location (location of highest rainfall accumulation) and the direction an distance connecting these two points becomes the inflow vector associated with the storm. For the example shown in Figure 10, the inflow vector for the Ashland, WI April 2001 storm is SSW at 560 miles.

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Figure 10. HYSPLIT Model trajectory example 5.3.7 In-place storm maximization process Storm maximization is the process of increasing rainfall associated with a historical observed extreme storm under the potential condition that additional moisture could have been available to the storm for rainfall production.

This is accomplished by increasing the surface dew points to some climatological maximum and calculating the enhanced rainfall amounts that could potentially have been produced if those enhanced amounts of moisture had been available when the storm occurred. In this calculation, surface-based dew points were used in the maximization calculations. The dew points were subsequently adjusted to the elevation of the storm location. This was done to remove the amount of moisture associated with the analyzed dew point that would not be available NF-3.5-2B Page 36 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 below that elevation, as the moisture associated with those values represents moisture in the atmospheric column above ground level.

An additional consideration is usually applied that selects the climatological maximum dew point for a date 15 days towards the warm season from the date that the storm actually occurred. This procedure assumes that the storm could have occurred 15 days earlier or later in the year when maximum dew points (and moisture levels) are higher. This assumption follows HMR guidance and is consistent with procedures used to develop PMP values in all the current HMR, as well as all AWA PMP studies.

HMR and WMO procedures for storm maximization use a representative storm dew point as the parameter to represent available moisture to a storm (assuming the atmosphere is saturated). Storm precipitation amounts are maximized using the ratio of precipitable water for the maximum dew point to precipitable water for the observed storm representative dew point.

Maximum dew point climatologies are used to determine the maximum atmospheric moisture that could have been available. This study utilized the 6-, 12-, and 24-hour average 100-year recurrence interval dew point climatology developed during the Nebraska statewide PMP study (Reference 24) and updated during the Ohio statewide PMP study (Reference 25). Figure 11 displays an example of the 24-hour 100-year recurrence interval dew point climatology for the month of July. Similar maps for each month of the year for each duration (6-, 12-,

and 24-hours) were utilized and are provided in Attachment 4.

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Figure 11. July 24-hour 100-year recurrence interval dew point climatology Observed storm rainfall amounts are maximized using the ratio of precipitable water for the maximum dew point to precipitable water for the storm representative dew point, assuming a vertically saturated atmosphere. The ratio of the maximum precipitable water and actual precipitable water is converted into a percent and the storm rainfall totals as they occurred are maximized by this value. This value is called the in-place maximization factor (IPMF). By definition, IPMFs are always greater than or equal to 1.

The storm representative dew point was derived for each of the events analyzed during this study either by the USACE/NWS or AWA during previous work. The HYSPLIT trajectory model provides detailed analyses for determining the upwind trajectories of atmospheric moisture that was advected into the storm being analyzed.

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Using these trajectories, the moisture source location is determined. The procedures followed are similar to the approach used in HMRs. However, by utilizing the HYSPLIT model trajectories, much of the subjectivity is eliminated. Once the general upwind location of the moisture source region feeding into the given storm event was determined, the hourly surface observations were analyzed for all available stations/reports within the vicinity of the inflow vector and general region.

Once the moisture source region is identified, hourly surface dew point observations are gathered and analyzed over the general region where the moisture originated from. These surface-based dew point values are adjusted to the 1,000mb level (approximately sea level). In addition, the total storm isohyetal pattern is displayed, along with the HYSPLIT trajectories. For storm maximization, average dew point values for the appropriate duration which was most representative of the actual rainfall accumulation period for an individual storm (6-, 12-, or 24-hour) was used to determine the storm representative dew point. To determine which time frame was most appropriate, the total rainfall amount was analyzed. The duration (6-, 12- or 24-hour) closest to when approximately 90% of the rainfall had accumulated was used to determine the duration used, i.e. 6-hour, 12-hour, or 24-hour. From these data, the appropriate dew point value representing the x-hour average value was determined which best represents the core rainfall period associated with the storm being analyzed. The storm representative dew point value is typically an average of two or more stations in a given region where the values are showing consistency in time and space. In Figure 12, the region chosen is circled in red. The center of this region then becomes the storm representative dew point location. The line connecting this point with the storm center location (point of maximum rainfall accumulation) is termed the moisture inflow vector. The moisture inflow vector is then used in the moisture transposition calculation process PMP.

The storm spreadsheets presented in Attachments B1, C2, and D3, list the moisture source region for each storm and dew point values used in the maximization calculations. Figure 12 is an example map used to determine the storm representative dew point for the Duluth, MN June 2012 storm event.

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Figure 12. Surface dew point 12-hour average observations used in the storm representative dew point analysis for the Duluth, MN June 2012 storm event 5.3.8 Storm transposition adjustment process Once each storm is maximized in-place, it is then transpositioned from its original location to the site. Transfer of a storm from where it occurred to a location that is meteorologically and topographically similar is termed storm transpositioning (e.g., HMR 51, Section 2.4.1 Reference 1). The transpositioning process provides a way to quantify how much rainfall the storm would have produced over the MNGP basin and at the MNGP site had it occurred there instead of its original location. In this transposition process, differences in moisture and elevation between the original location and the site are accounted for and quantified. For a given storm event to be considered transpositionable, there must be similar meteorological/climatological and topographical characteristics at its original location versus the new location. This is a qualitative measure and is left up to the judgment of the meteorologist performing the analysis. AWA provides exceptional experience and capability to analyze storms in this region and assess the transposition limits of each event in relations to the MNGP basin and MNGP site location.

It is also important to note that AWA always chooses the most conservative transposition limits (i.e., a larger potential domain of influence) for storms that are in question or near boundaries unless further analysis or data NF-3.5-2B Page 40 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 can be used to justify including or not including an individual storm. This is because the transposition process requires a binary answer, a storm is either transpositionable to a location or not. However, in the science of meteorology, the limits follow more of a transitional process where gradients exist. Therefore, utilizing a more conservative approach (i.e., larger transposition limits) compensates for these potential unknowns.

Extreme rain events that occurred over topographically and meteorologically/climatologically similar regions surrounding a study area are a very important part of the historical evidence on which PMP estimates are based.

Study locations usually have a limited period of record for rainfall data collected at that location and hence have a limited number of extreme storms that have been observed. As such, the storm transpositioning process uses additional space to compensate for the limited time frame of instrumental climate records at any location. Storms observed regionally with similar meteorology and topography are analyzed and adjusted to provide information describing the storm rainfall as if the storm had occurred over the study location. The underlying assumption is that storms transposed to the study area could have occurred over the study area location under similar meteorological conditions. This decision is made using scientific judgment related to the storm type, season of occurrence, similarity of topography between the two locations, and experience analyzing past storms. To properly relocate such storms, it is necessary to address issues of similarity as they relate to topography and atmospheric moisture availability, and make appropriate adjustments. The adjustments which calculate the difference between the original storm location and the MNGP location are calculated following the process described in Section 5.3.9.1 and shown in equation 3. This process is also detailed in HMR 51 Section 2.4.3 (Reference 1).

The same maps used for maximum dew points during the IPMF process were used in the storm transpositioning calculation. The procedure for deriving the climatological maximum dew points for use in calculating the transposition maximization ratio uses information derived during the calculation of the IPMF. The moisture inflow vector connecting the storm location with the storm representative location was transpositioned to the CNP site for each storm. The value of the maximum dew point at the upwind location provided the transpositioned maximum value used to compute the transposition adjustment factor for relocating the storm to the site. The resulting moisture transposition factor (MTF) can be greater than or less than 1, depending on whether the transpositioned location and inflow vector produced higher or lower maximum dew point values and while taking into account the difference in elevation between the two locations.

5.3.9 Total adjustment factor calculation and use of the storm spreadsheet AWA has developed Excel spreadsheets for each storm used in this calculation, which incorporates relevant storm information, automatically calculates appropriate adjustment factors, and computes the adjusted values for each storm. These adjusted values then become the basis for determining the PMP and LIP input values. Each storm spreadsheet used the observed storm rainfall amounts, storm representative dew points, maximum dew points (both in-place and transpositioned), storm elevation, and transposition location elevation information. Using the storm center location and inflow vector, the in-place and transpositioned maximum dew point values were determined. This information was entered into the storm spreadsheet to calculate the IPMF, the MTF, and finally the total adjustment factor (TAF). The TAF is a product of the IMPF and MTF and produces a value that represents what the amount of rainfall would have been for a given storm had it occurred over the site instead of its original location. This TAF was applied to the observed storm rainfall values to provide the final adjusted values for the maximized and transpositioned storm rainfall for a given storm.

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 5.3.9.1 Moisture maximization calculations The adjusted rainfall for a given storm event was determined by applying a TAF to the observed rainfall value. The TAF is the product of the two storm adjustment factors, the IPMF and the MTF. These calculations were completed for all storms used in this analysis.

The available atmospheric moisture, in terms of precipitable water depth, must be determined for the storm center location to calculate both the IPMF and MTF. The IPMF is determined by taking the ratio of the maximum precipitable water depth at the storm representative dew point location to the storm representative precipitable water depth at the same location. The MTF is determined by taking the ratio of the maximum precipitable water depth at the transposition dew point location to the maximum precipitable water depth at the storm representative dew point location. Note that in the final TAF calculation, the precipitable water depth at the storm center is used in both the numerator of the IPMF and denominator of the MTF and is ultimately canceled out of the equation, having no impact on the TAF. However, it is still important to calculate the storm center precipitable water and the MTF and IPMF individually, so that each component can be quantified for completeness and quality/error control purposes.

The precipitable water depth is calculated from a lookup table stored within the storm adjustment spreadsheets.

The lookup table is a digital version of the precipitable water table found in the WMO PMP manual (Reference 28) with dew point temperatures for elevations from sea level to 30,000 feet (Equation 1).

(Equation 1)

In-place storm maximization is applied to each storm event using the methodology described in Section 2.2. Storm maximization is quantified by computing the IPMF using Equation 2.

(Equation 2)

Where:

Wp,max = precipitable water for the maximum dew point; and Wp,rep = precipitable water for the representative dew point.

The change in available atmospheric moisture between the storm center location and the site is quantified as the MTF. The MTF is calculated as the ratio of precipitable water for the maximum dew point at the MNGP basin centroid for PMP and MNGP site for LIP to precipitable water for the storm maximum dew point at the storm center location using Equation 3.

(Equation 3)

Where:

Wp,trans = precipitable water at the target location; and Wp,max = precipitable water at the storm center location.

NF-3.5-2B Page 42 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 The TAF is a product of the linear multiplication of the IPMF and MTF. The TAF is a combination of the total moisture difference and terrain influences on rainfall when maximized and transpositioned to the MNGP basin centroid for PMP and MNGP site location for LIP.

(Equation 4) 5.3.10 Storm spreadsheet development process AWA has developed an Excel spreadsheet for each storm on the short storm list which incorporates relevant storm information, automatically calculates appropriate adjustment factors, and computes the adjusted rainfall DAD table. These storm spreadsheets used the observed storm DADs, storm representative dew points, maximum dew points (both in-place and transposition), storm elevation, and transposition location elevation information either as published in the USACE Storm Studies reports, HMR 51 tables, or as developed during AWA SPAS storm analyses. This information was entered into individual storm spreadsheets, one for each short list storm at the basin centroid. Using the storm center location and inflow vector, the in-place maximum dew point was determined. The same inflow vector was then moved to the basin centroid to determine the transpositioned maximum dew point value and total adjustment factor for that storm. This information was entered into the storm spreadsheet to calculate the in-place maximization factor, the transposition factor, and finally the total adjustment factor. This total adjustment factor was applied to the storm DAD table values to provide the final adjusted DAD table for the maximized and transpositioned storm rainfall values at each location.

Once all the storms were adjusted to the basin centroid, DA and DD plots were constructed for analysis and envelopment. This ensured spatial and temporal continuity of the PMP values for the basin. Attachments 1, 2, and 3 include the storm spreadsheets developed for each storm transpositioned to the basin centroid. Figure 13 displays an example storm spreadsheet for the Big Rapids, MI September 1986 Fall River, KS June 2007 adjusted to the basin centroid.

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 NF-3.5-2B Page 44 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 NF-3.5-2B Page 45 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Figure 13. Storm spreadsheet for Fall RiverBig Rapids, KS MI June 2007September 1986 transpositioned to the basin centroid 5.3.11 Development of PMP values Storm maximization and transposition provide an indication of the maximum amount of rainfall that a particular storm could have produced at any location within the region analyzed for the MNGP watershed. Use of these values alone does not ensure that PMP values are provided for all area sizes and durations since some of the maximized and transpositioned values could be less than the PMP. By enveloping the rainfall amounts from all the major storms, rainfall values indicative of the PMP magnitude are produced. The standard process for deriving a DAD table (Reference 1, Reference 28) of PMP values at the basin centroid was used in the project.

5.3.11.1 Envelopment procedures and DAD development Enveloping is a process for selecting the largest value from a set of data. This technique provides continuous smooth curves based on the largest rainfall values from the set of maximized and transpositioned storm rainfall values. The largest rainfall amounts provide guidance for drawing the curves.

During the enveloping process, values which are not consistent (are either high or low) are re-evaluated to insure reliability. High values are enveloped unless an explanation can be provided to justify undercutting the value. No undercutting of rainfall values was done in this calculation. Low values are also re-evaluated for reliability and then enveloped to maintain consistency with surrounding values. Enveloping the largest adjusted storm values ensures that PMP is achieved at all area sizes and durations. This is necessary because the limited storm record (approximately 150 years of data) in the region transpositionable to the PINGP MNGP basin may not have recorded a storm event that would result in PMP at certain area sizes and durations. The result of this envelopment procedure is a set of smooth curves that maintain continuity among temporal periods and areal sizes.

The envelopment process was used in PMP determination for this calculation, following the same procedures used for envelopment in the derivation of PMP in the HMRs (Reference 1), the WMO PMP Manual (Reference 28), and previous AWA PMP studies (Reference 15, Reference 25). Once the total storm adjusted rainfall values for the appropriate storms were determined, they were plotted on individual DA charts for each duration for analysis.

Envelopment was applied to each DA curve for each duration. The DA envelopment curves were drawn to provide continuity in space. Figure 14 is an example of an all-season DA chart and Figure 15 is an example of a cool-season DA chart with the envelopment curve plotted on both for the 24-hour duration at the MNGP watershed basin centroid.

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Figure 14. 24-hour all-season Depth-Area curves at the MNGP basin centroid NF-3.5-2B Page 47 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Figure 15. 24-hour cool-season Depth-Area curves at the MNGP basin centroid The second application of the envelopment process was used with the DD curves. Curves for each area size were constructed using results from the DA analysis described previously the basin centroid for the all-season storms and the cool-season storms. The DD curves were drawn to produce smooth curves that provide continuity in time among all durations. Figure 16 and Figure 17 display the DD curves for the basin centroid all-season and cool-season PMP. All DA and DD charts developed during this calculation are included in Attachment 7. The final set of DD curves for all durations at the basin centroid defines the initial set of PMP values for both all-season and cool-season PMP. The envelopment of the adjusted storms together with the curve smoothing process insured that all storm data were included and that the resulting set of PMP values provides rainfall values that are consistent spatially and temporally.

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Figure 16. All-season Depth-Duration curves at the MNGP basin centroid NF-3.5-2B Page 49 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Figure 17. Cool- season Depth-Duration curves at the MNGP basin centroid 5.3.12 Local Intense Precipitation Analysis LIP calculated for the 1-hour and 6-hour 1-square mile PMP for the MNGP site location. This analysis followed the storm-based approach as used in the overall PMP development and as described in HMR 51 (Reference 1) and HMR 52 (Reference 2). The storm-based approach utilizes actual data from rainfall events which have occurred over the site and in regions transpositionable to the MNGP location. These rainfall data are maximized in-place following standard maximization procedures, then transpositioned to the MNGP location as described in Sections 5.3.7, 5.3.8, and 5.3.9. The transpositioning process accounts for differences in moisture and elevation between the original location and the MNGP site. The process produces a total adjustment factor that is applied to the original rainfall data for each storm. The result represents the maximum rainfall each storm could have produced at the site had all factors leading to the rainfall been ideal and maximized. Information is included in this section detailing the storms used, how they were analyzed, and how the LIP values were derived. Information on each storm event evaluated for LIP development is included in Attachment 3.

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 5.3.12.1 Local Intense Precipitation Development The PMP values provided in HMR 51 for the MNGP site provide values starting at 6-hours and 10-square miles.

There are no explicit values provided at the 1-hour duration and/or 1-square miles. HMR 52 (Reference 2) provides information to derive the 1-hour 1-square mile values based on HMR 51 6-hour 10-square mile PMP values. Unfortunately, the most recent storm evaluated in HMR 51 occurred in 1972, with the most recent LIP storm from HMR 52 occurring in 1973. In addition, HMR 51 and HMR 52 both cover a large and diverse domain, and generalization was necessarily employed in the development of the respective PMP and LIP values. In addition, because HMR 51 and HMR 52 covers a large and diverse domain, and generalization was necessarily employed in the development of the respective PMP and LIP values. This resulted in LIP values which were influenced by storms not appropriate for the MNGP site (e.g. Smethport, PA July 1942) and therefore are not accurate values for the MNGP site.

This site-specific LIP analysis corrects many of the issues in the HMRs by explicitly evaluating storms which are directly transpositionable to the MNGP site. In addition, the understanding of the meteorology of these events has advanced significantly since HMR 51 was published. These corrections and the updated storm database were employed in this calculation. In addition, the results and data from numerous SPAS storm analyses used in the PMP development during this calculation and several others in the region were used extensively in this analysis.

5.3.12.1.1 Local Intense Precipitation Storm List The initial step in the development of the LIP values was to identify a set of storms which represent rainfall events that are LIP-type local storm events. This included storms where extreme heavy rainfall accumulated over short durations and small area sizes. These include thunderstorms and intense rainfall associated with MCC and individual thunderstorms. This procedure is similar to what is described in HMR 52 Section 6.

AWA evaluated all storms used in previous PMP studies in the region considered transpositionable to the MNGP location to develop a list of the storms needed for proper LIP evaluation and determination. The same evaluations were considered in the transposition evaluations as used in the PMP development. Factors such as elevation differences of more than +/- 1,000 feet and/or distances of more than +/- 6° latitude were considered. These factors follow guidance in the HMRs (Reference 1, Reference 12, Reference 13). A few storms with storm centers in the southern Great Plains and Midwest were included even though they were slightly more than 6° latitude difference than the basin centroid latitude. This is because these storms are of the same type (individual thunderstorms and MCCs) that would be expected over the basin and could produce LIP. In these situations, the conservative assumption is employed and the storm is allowed to be used in the PMP calculations. This applied to both cool-season and all-season storm transposition considerations. Finally, the storm type was evaluated. Storm types which would not result in a PMP/PMF scenario for the large MNGP watershed were not considered. This included storms which were individual MCS and thunderstorms. This resulted in 20 events being evaluated (Table 6). Twelve of these storms were previously analyzed in HMR 33 (Reference 27), HMR 51 (Reference 1), and HMR 52 (Reference 2) by the NWS and USACE. The remaining 8 were analyzed using SPAS program during previous LIP calculations.

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CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Table 6. Local Intense Precipitation storm list 5.3.12.1.2 Local Intense Precipitation Calculation Process Most of the 16 storms analyzed by the NWS/USACE did not contain explicit 1-hour 1-square mile data. This is the result of a lack of hourly recording information available during the original analyses. To correct for this, information presented in HMR 52, Section 6 was utilized. This information provided ratios which allowed for the computation of the 1-hour 1-square mile value to be derived from the 6-hour 10-square mile value (HMR 52 Figure 23, Reference 2). Although these ratios were derived to apply to the HMR 51 PMP values, they are implicitly relevant for use in this calculation because both processes are using the same data set and following the storm-based approach, i.e. it is only a scaling variation that is occurring. No inherent change or adjustment to the data is taking place that would result in a different data set or storm type. For the Bonaparte, IA June 1905 and Holt, MO June 1947 storm events analyzed by the NWS/USACE (Reference 6), explicit 1-hour data was available and therefore no ratio application was required. The 8 storms analyzed using SPAS allowed for explicit hourly rainfall to be evaluated with a spatial resolution of 1/3rd square mile. This provided data for the storm rainfall 1-hour 1-square mile area sizes to be explicitly evaluated.

Once all the storms were identified and their 1- and 6-hour 1-square mile values derived, the final step in the process was to maximize each storm specific to the MNGP location. This was a two-step process. First, the in-place maximization factor was calculated. This provides a value that is applied to the observed storm values which represents what the storm would have looked like had the atmospheric conditions and moisture been at maximum levels when the storm occurred. Next, the resulting in-place maximized values for each storm needed to be adjusted as if the storm had occurred over the MNGP site. To accomplish this, the transposition calculation process was followed to adjust the storm from its original location to the MNGP site. The transposition calculation adjusts for differences in available moisture both in the horizontal (north/south and east/west directions) and vertical NF-3.5-2B Page 52 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 (differences in elevation) at the site versus the original storm location. All the calculations and resulting values for each storm used in the LIP analysis are provided in Attachment 3.

After the maximization and transposition factors were calculated for each of the storms, the results were applied to the maximum 1- and 6-hour value for each storm to calculate the maximized 1-hour 1-square mile values. The largest of these values results in the site-specific LIP for the MNGP site. After adjustments were applied, the Holt, MO June 1947 storm event had the highest 1-hour rainfall, while the David City, NE June 1963 storm had the highest 6-hour rainfall. In both cases, several other storms providing slightly smaller values and support for this value. For final application of the LIP hydrology, the 1-hour value is then required to be split into sub-hourly increments of 5-, 15-, 30-minutes. Updated evaluations of the appropriate amount of rainfall to assign to each increment for the site based on storm data would have been ideal. However, a lack of sub-hourly PMP-type storm data from the storms analyzed by the NWS/USACE prevented an updated evaluation from being completed.

Therefore, it is recommended that the ratios derived in HMR 52 be applied at the MNGP site (HMR 52 Figures 36-38, Reference 2).

5.3.12.2 Local Intense Precipitation Results The previous sections provided details on the selection and maximization of the storms used in this analysis. The results of this analysis resulted in the Holt, MO June 1947 and David City, NE June 1963 storm events having the highest 1- and 6-hour maximized rainfall values at the 1-square mile area size of all the storms evaluated. Table 7 provides the final PMP values for 1- and 6-hours 1-square miles and the subsequent sub-hourly values using the data calculated in this calculation.

Table 7. Site-Specific Local Intense Precipitation NF-3.5-2B Page 53 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 5.3.12.2.1 Reason for reduction from HMR 52 Local Intense Precipitation values This site-specific LIP calculation provided differences in LIP values from those presented in HMR 52 (Reference 2).

All else being equal, if only more storms were added to those used in HMR 51/52, the values would only be the same or higher. However, this calculation explicitly addressed elevation, used updated maximization factors, and explicitly defined transposition limits for each storm considered.

Since the site-specific analysis followed the same basic storm rainfall adjustment procedures as HMR 51 and HMR 52, it would be useful to understand the cause of the differences in the values. Working papers are not available for HMR 51 or HMR 52, so explicit differences in calculations and procedures cannot be evaluated. However, the following methods and data were treated differently between the studies:

1) HMRs 51 and 52 provide generalized and smoothed LIP values over a large geographic domain that covers the United States east of the 105th meridian. Specific characteristics unique to the MNGP watershed and the MNGP site were not addressed. This calculation considered characteristics specific to the site, and produced PMP values that explicitly considered the meteorology of the PMP storm type which would result in the 1-and 6-hour 1- square mile area size LIP values.

2) The transposition limits of the Smethport, PA July 1942 (Reference 30), which produced the 4- and 6-hour world record rainfall, were not allowed to influence the LIP values at the MNGP site. The refined transposition limits used in this calculation result in lower LIP values compared to HMR 52 for locations where the Smethport storm apparently influenced PMP values in HMR 51. Smoothing of the PMP/LIP isolines in HMRs 51 and 52 necessarily had to encompass the Smethport maximized in-place rainfall far beyond its explicit transposition limits. Note, Section 3.2.4 of HMR 51 states that they "slightly undercut" the maximized 6-, 12-, and 24-hour values by up to 7% to avoid "excessive envelopment of all other data in a large region surrounding the Smethport location." This over envelopment effect extended well beyond the intended transposition limits of the Smethport storm because the PMP/LIP isolines required smoothing and fitting over surrounding regions.

3) Each storms inflow vector was re-evaluated and combined with an updated set of dew point climatologies and when necessary, updated storm representative dew point values were used for the in-place maximization and transposition factors. The HYSPLIT trajectory model (Reference 7) was used to evaluate moisture inflow vectors for storms on the short storm list. Trajectory models were not available in previous HMR studies. Use of HYSPLIT allowed for a high degree of confidence when evaluating moisture inflow vectors and storm representative dew points.

4) Several new storms have been analyzed and included in this LIP analysis that were not included in HMRs 33, 51, and 52. This provided a higher level of confidence in the final PMP values. Further, this allowed for a refined set of values that better represent the LIP estimates at the site. This expanded the data set used to derive LIP includes a large number of recent storms.

5) The calculation provided adjustments for storm elevation to the nearest 100 feet of elevation, whereas HMRs 51 and 52 made no explicit adjustment for elevation. This adjustment depends on the elevation of the historic storm's maximum rainfall location and therefore varies from storm to storm. Further, the elevation at the MNGP site was determined in this analysis, providing more accurate calculations to account for differences in available atmospheric moisture due to elevation differences between the original NF-3.5-2B Page 54 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 storm location and the site. Note that each 100 feet of elevation change equates to approximately a 0.8%

difference in the maximization factor.

6) Storms analyzed by the NWS/USACE which occurred prior to 1948 and used 12-hour persisting dew points in the storm maximization process were adjusted so that the updated dew point climatology could be utilized consistently. For thunderstorms and MCC storm events 7°F was added to the NWS/USACE storm representative dew point. This was done to adjust for using average dew point values for varying durations vs. 12-hour persisting dew point values. Evaluations of 12-hour persisting storm representative dew points showed those used in HMR 51 underestimated the storm representative values used in storm maximizations.

5.3.13 Site-Specific PMP values calculated during this study This calculation has produced PMP values for use in computing the PMF for the MNGP watershed. Values for all durations and area sizes provided in HMR 51 and for the area size specific to the basin have been computed using the procedures described in this report. These include durations of 6-, 12-, 24-, 48-, and 72-hour durations and area sizes from 10-square miles to 100,000-square miles. AWA has provided a comparison of the PMP values to HMR 51 PMP values at the centroid of the basin at area sizes where information is available. This comparison is provided in Table 8. The all-season PMP values calculated are included in Table 9 and the cool-season PMP values calculated are included in Table 10. Comparisons of the cool-season PMP values against an appropriate HMR are not provided because HMR 51 does not provide explicit cool-season PMP values and no other HMR provides explicit cool-season PMP values. Instead, cool-season PMP values are derived using ratios based on seasonality analysis from HMR 33 and HMR 53 applied to the all-season PMP. This process is significantly different from deriving cool-season PMP values using a storm based, deterministic approach and therefore it is not appropriate to compare the cool-season PMP values derived in this study to those using seasonality methods.

NF-3.5-2B Page 55 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Table 8. Site-Specific All-Season Probable Maximum Precipitation compared to HMR 51 values Table 9. Site-Specific All-Season Probable Maximum Precipitation NF-3.5-2B Page 56 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Table 10. Site-Specific Cool-Season Probable Maximum Precipitation 5.3.14 Controlling storms for the Site-Specific PMP values Several different storm events control the PMP values at various area sizes and durations. This was expected in this type of storm-based PMP analysis. In this situation, a single storm would not be expected to have occurred that contained moisture and storm dynamics at the most efficient levels for all area sizes and durations. Instead, it is expected that one or more of those events would be very efficient at short durations (less than 24-hours), one or more would be very efficient at medium durations (24- to 48-hours), and one or more would be very efficient at the longest durations (72-hours). Then, by combining those most efficient storms as if they were a single PMP storm event, the largest of the maximized storms at each duration and area size have been used to determine the PMP values. This allows the PMP values for the basin to reach the theoretical upper limit threshold. Table 11 and Table 12 display the storms which control the PMP values at the standard HMR 51 area sizes and durations for the all-season and cool-season PMP depths. Refer to Table 4 and Table 5 under the column titled AWA Storm Number for the information on each of these controlling storms.

Table 11. Site-specific all-season Probable Maximum Precipitation controlling storms NF-3.5-2B Page 57 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Table 12. Site-specific cool-season Probable Maximum Precipitation controlling storms 5.3.14.1 Comparison of the all-season PMP against precipitation frequency estimates Site-specific PMP values from the basin centroid location were compared with 24-hour 100-year recurrence interval rainfall values as a general check for reasonableness. The ratio of the 10-square mile 24-hour PMP to the 24-hour 100-year recurrence interval rainfall amounts is generally expected to range between 2 and 4, with values as low as 1.7 and as high as 5.5 found in HMRs 57 and 59. Further, as stated in HMR 59 the comparison indicates that larger ratios are in lower elevations where short-duration, convective precipitation dominates, and smaller ratios in higher elevations where general storm, long duration precipitation is prevalent (HMR 59 Section 11.1).

Comparison of PMP values with rainfall frequencies is made for point locations, i.e., individual locations. Sufficient data are not available to make the comparison at other area sizes. For example, comparisons for the actual area size of the entire basin would be more useful for this task, but return frequency statistics are not available for spatial areas larger than point locations. Values above four indicate that the PMP values are relatively large compared with the return frequency values (i.e. are conservative).

The 100-year 24-hour recurrence interval rainfall values are derived from NOAA Atlas 14, Vol. 8 produced by the National Weather Service (Reference 9). Comparison of the all-season 10-square mile 24-hour site-specific PMP values with the 100-year 24-hour rainfall return frequency value was made. The site-specific 10-square mile, 24-hour PMP value of 21.0 inches was divided by the 100-year 24-hour value of 6.24 to derive the ratio for the basin centroid for both data sources. This resulted in a ratio of 3.4:1, within the expected range of 2 to 4.

5.3.15 Reasons for reductions of all-season PMP values versus HMR 51 For every area size and duration, the all-season PMP values derived in this calculation resulted in reduced PMP values from those provided in HMR 51, with unique PMP values calculated for the cool-season PMP. This calculation explicitly addressed variations in meteorology and topography in regions outside of the basin where storms occurred that are considered to be transpositionable. All storms on the short storm list were re-evaluated to determine updated storm representative and maximum dew points.

Since this calculation followed the same basic storm rainfall adjustment procedures as HMR 51, it would be useful to understand the cause of the differences in the PMP values calculated during this calculation and those provided in HMR 51. Detailed working papers for the storms analyzed, the exact processes employed to derive the final NF-3.5-2B Page 58 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 values, and information used to derive PMP are not available for HMR 51, so explicit differences in calculations and procedures cannot be determined. However, the following issues were treated differently in this calculation:

HMR 51 provides generalized and smoothed PMP values over a large geographic domain covering the United States east of the 105th meridian. Specific characteristics unique to individual basins, such as the MNGP basin, were not addressed at the time. This calculation, however, considered characteristics specific to the basin, and produced PMP values explicitly considering the meteorology of the PMP storm type and topography of the region which would result in the PMF for the basin.

Each storms moisture inflow vector was re-evaluated and combined with an updated set of storm representative dew point values and climatology values. When necessary, updated storm representative dew point values were used in the calculation of in-place maximization and transposition factors. The HYSPLIT trajectory model was used to evaluate and verify moisture inflow vectors for storms on the short storm list. The trajectory model was not available for use in HMR studies. The use of HYSPLIT allowed for a high degree of confidence when determining moisture inflow vectors and storm representative dew points.

Several new storms have been analyzed and included in this site-specific PMP calculation that were not included in HMR 51. This provided a higher level of confidence in the final PMP values. Further, this allowed for a refined set of values that better represent the PMP values for both the all-season and cool-season PMP scenarios, as the data set used to derive PMP has been expanded to include a larger set of more recent storms.

The site-specific PMP calculation provided adjustments for storm elevation to the nearest 100 feet of elevation, whereas HMR 51 makes no explicit adjustment for elevation for PMP values. This adjustment depends on the elevation of the historic storm's maximum rainfall location and therefore varies from storm to storm. Further, the average basin elevation was evaluated in this calculation using GIS, providing an accurate representation and calculation to account for loss of available moisture up to that elevation.

SPAS was used in conjunction with NEXRAD data (when available) to evaluate the spatial and temporal distribution of rainfall. Use of NEXRAD data generally produced higher point rainfall amounts than were observed using only rain gauge observations and provides objective spatial distributions of storm rainfall for locations among rain gauges. SPAS results provided storm DADs, total storm precipitation patterns, and mass curves for the newly analyzed storms. Using these technologies, significant improvements of the storm rainfall analyses were achieved.

Previously analyzed storm events that occurred prior to 1948 that used 12-hour persisting dew points were re-evaluated to determine an updated storm representative dew point. This was done to adjust for using average maximum dew point values for varying durations vs. maximum 12-hour persisting dew point values. Recent evaluations of maximum 12-hour persisting storm representative dew points show those used in HMR 51 underestimated many of the storm representative dew point values. An updated set of maximum dew point climatology maps were produced.

NF-3.5-2B Page 59 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Only storm types that would explicitly produce a PMF event for the basin of this size were evaluated and included in the PMP development. Therefore, small area size, high intensity, short duration events were not included in the all-season and cool-season PMP calculations.

5.3.16 Recommendations for application of site-specific PMP and LIP values PMP and LIP values have been computed that provide maximum rainfall amounts for use in computing the PMF within the MNGP watershed and the maximum water levels at the MNGP site location. This calculation provided both all-season and cool-season PMP values. The cool-season PMP values are considered as a rain-on-snow scenario and are combined with a given amount of snow melt to derive the total runoff associated with a cool-season PMP rainfall.

The calculation addressed several issues that could potentially affect the magnitude of the PMP storm over basin as compared with HMR 51 (Reference 1). Analysis of moisture availability for previously analyzed storms and analysis of recent extreme storms with up to date state-of-the-science techniques resulted in PMP values which replace HMR 51 and provide explicit cool-season PMP values. These represent the most current PMP values that should be used together with the procedures in HMR 52 (Reference 2) and updated PMP design storm parameters to provide PMP rainfall at any location within the basin and at the site location.

HMR 52 uses a procedure for locating the largest amounts of rainfall associated with the PMP storm (Reference 2),

such that the largest volume of rain falls within the watershed boundaries. No restrictions or adjustments to those procedures are recommended from this study.

The storm search and selection of storms for the basin-wide PMP emphasized storms with the largest rainfall values covering large area sizes and long durations. Therefore, results of the all-season and cool-season PMP from this calculation should not be used for basin sizes where the PMF would potentially result from small area sizes, short duration intense rainfall. This would include basins affected by individual thunderstorms or MCC storm types.

The LIP values were derived using storms with high intensity, short duration rainfalls, such as individual thunderstorms and MCCs. They were calculated based on the specific meteorological and topographical characteristics unique to the MNGP site. Therefore, use of the LIP values at other locations or where other storm type(s) would control LIP values is not recommended.

5.4 Meteorological Time Series Development AWA used a procedure to determine the maximum temperature, maximum dew point temperature, and maximum wind speed for each of the Monticello and Monticello basins for three historic rainfall/flood events which best represent an expected cool-season PMP rainfall scenario (April 1954, April 1965, and April 2001). Hourly time series were created for a 120-hour period. This duration encompassed the maximum 72-hour precipitation period needed for PMF rain-on-snow modeling. The hourly temperature and dew point values were maximized to ensure continuity with the similar maximized PMP rainfall amounts using the average in-place maximization temperature difference of the cool-season storms used to derive PMP. This represented the average temperature difference between the storm representative dew point and the climatological maximum dew point. This was done in order NF-3.5-2B Page 60 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 to best represent what the meteorological parameters would look like during a cool-season PMP rainfall event and to be consistent with the maximizations of the storm events used to derive those values. This process followed the same procedures as were completed during PMP studies where rain-on-snow PMP was determined (e.g. Reference 15, Reference 24, Reference 25).

5.4.1 Data and Methods Hourly reporting surface stations were identified in and around the Monticello and Monticello basin. Only those stations considered NWS official stations and representative the regional climate were included. Initially, all meteorological stations within a latitude/longitude box of 48.5°N/98.0°W to 41.0°N/88.0°W were identified for each storm event analyzed. Only those stations considered representative to each sub-basin's climate were included (Figure 18, Figure 19, Figure 20). The hourly data were extracted from on-line resources, quality controlled, and assembled into a consistent format. For April 1965, some hourly stations only recorded data every three hours, in order to get a complete hourly time series, data were linearly interpolated between observations.

Figure 18. Stations used in the April 1954 meteorological time series development NF-3.5-2B Page 61 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Figure 19. Stations used in the April 1965 meteorological time series development NF-3.5-2B Page 62 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Figure 20. Stations used in the April 2001 meteorological time series development 5.4.1.1 Hourly time series The hourly stations used in this analysis were quality controlled to ensure all data used had no missing hours and erroneous values. The data were then assembled into a consistent format using Excel for efficient analysis. Hourly precipitation data were collected from hourly gridded precipitation data generated from SPAS. The hourly rainfall data were used to determine the maximum 72-hour rainfall window to associate with the cool-season PMP analysis period.

In order to determine the proper 72-hour timing, an indexing approach was used because the maximum 72-hour rainfall did not always occur at the same time and each storm had different durations. To overcome the duration NF-3.5-2B Page 63 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 differences, precipitation start time, and peak 72-hour rainfall variability from all storms were normalized to have a similar index period of 120-hours. For each storm, the index time of the maximum 72-hour accumulated rainfall was determined (green line, Figure 21). The 72-hour mid-point was determined by shifting the maximum 72-hour accumulated rainfall index hour 36-hours earlier (red line, Figure 21). The 72-hour mid-point was used to determine the start and end times/index hours of the 120-hour analysis window (blue lines, Figure 21). This procedure was performed on the three storm events in order to make comparisons for the 72-hour PMP meteorological time series profile.

Figure 21. Example of methodology to create normalized profiles. Maximum 72-hour accumulated precipitation (green line). Mid-point of 72-hour window based on 36-hour shift from maximum 72-hour accumulation (red line). Start and end point of the 120-hour duration used in analysis (blue lines).

Once the proper 120-hour window was identified for each storm, hourly data were grouped together into an Excel spreadsheet. An example of a hourly station data for KSTC April 1954 is shown in Table 13. In addition to the hourly tables created for each station, plots of hourly temperature, dew point, wind speed, and rainfall were created. An example of plotted hourly station data for KSTC April 1954 is shown in Figure 22.

NF-3.5-2B Page 64 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Table 13. Example of hourly station data for KSTC, April 1954 Figure 22. Example of plotted hourly station data for KSTC, April 1954 5.4.1.2 Temperature time series maximization For each of the three storm events analyzed (April 1954, April 1965, and April 2001), a maximum time series was created based on calculating the maximum individual hourly station meteorological data of the stations used in different areas of the overall basin. For example, three stations for the April 1954 time series, KSTC, KMSP, and KDLH, were compared. The maximum of these three stations hourly meteorological data were used to create the maximum time series profile for the area of the basin they represent meteorologically for April 1954. The same NF-3.5-2B Page 65 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 process was then completed for the other two events, with the maximum at each hours used in the final analysis.

The final application of maximization for the meteorological time series was to apply the average temperature difference between the storm representative dew point value of each cool-season PMP storm against the maximum dew point climatological value. The values associated with the storms which control the cool-season PMP values were averaged and the resulting value was then applied to each hourly temperature value. The value derived from this process was 4.0°F. This was the value applied in the maximization process to the temperature and dew point hourly time series used in the snow melt calculations.

5.4.1.3 Creation of gridded time series datasets Gridded datasets were produced for the 120-hour time series using the maximum temperature, dew point, and wind speeds described in the previous sections. ArcGIS desktop 10.2 (Reference 10) was used to interpolate continuous gridded data between each of the station locations for the three analyzed storm events over the MNGP watershed. The final gridded datasets were converted to ASCII format. All geographic data used in these procedures utilized the World Geodetic System 1984 (WGS 84) spatial reference. The gridded time series data sets were produced using the following geoprocessing procedures:

1) For each storm, an Excel spreadsheet was composed containing the station data for each of the 120 hourly time steps. A separate sheet was created for each meteorological parameter (Ta, Td, and Ws).

2) Point features were created for each station using the Make XY Event Layer tool. Each parameter was stored as a separate feature class with each hour stored as a separate attribute. NoData values were ignored.

3) The Spline Spatial Analyst tool was used to interpolate raster datasets from the station point features for each storm/parameter. The tension spline type was used with the weight set to 500 and number of points set to 12. These relatively tight settings ensured the gridded data adheres to the station point values at the station locations without exaggerated inflation or deflation of values between station points. The output rasters were created in the GRID format with a spatial resolution of 30-arc seconds and were masked to the study area domain.

4) The temperature and dew point GRIDs were maximized by adding 4° to the value of each grid. This was done using the Plus Spatial Analyst tool and adding 4 to the value of each GRID.

5) For each parameter, the maximum gridded values from each of the three storms were taken. This was done using the Mosaic to New Raster tool with the Maximum mosaic operator.

6) For each parameter, the hourly GRIDs were converted to ASCII format using the Raster to ASCII conversion tool.

For quality control, if any dew point (Td) values were interpolated to be greater than the temperature (Ta) values, they were reassigned to match the Ta values. This was done using the Con() map algebra function. For each parameter, values were extracted at four control points over the grid domain; 1 - the northern region (47.5°, -

94.5°), 2 - the centroid of the domain (45.5°, -97.6°), 3- the MNGP site (45.3°, -93.9°), and 4 - the MNGP site (44.6°,

-92.6°) as shown in Figure 23. The extracted data were plotted over the 120-hour duration at each of the four points for analysis and comparisons. These results are displayed in Figure 24, Figure 25, Figure 26 and Figure 27.

NF-3.5-2B Page 66 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Figure 23. Four points used for QC of the meteorological time series data NF-3.5-2B Page 67 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 1 - Northern Basin (47.500°, -94.500°)

80 70 60 50 Temperature (°F) 40 Dew Point (°F) 30 Wind Speed (mph) 20 10 0

0 10 20 30 40 50 60 70 80 90 100 110 Figure 24. Maximized meteorological time series data for the northern portion of the basin 2 - Basin Centroid (45.455°, -93.642°)

80 70 60 50 Temperature (°F) 40 Dew Point (°F) 30 Wind Speed (mph) 20 10 0

0 10 20 30 40 50 60 70 80 90 100 110 NF-3.5-2B Page 68 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Figure 25. Maximized meteorological time series data for overall basin centroid 3 - Monticello Site (45.334°, -93.849°)

80 70 60 50 Temperature (°F) 40 Dew Point (°F) 30 Wind Speed (mph) 20 10 0

0 10 20 30 40 50 60 70 80 90 100 110 Figure 26. Maximized meteorological time series data at the Monticello site 4 - Prairie Island Site (44.622°, -92.633°)

80 70 60 50 Temperature (°F) 40 Dew Point (°F) 30 Wind Speed (mph) 20 10 0

0 10 20 30 40 50 60 70 80 90 100 110 NF-3.5-2B Page 69 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 Figure 27. Maximized meteorological time series data at the Monticello site 6.0 Final Results The following summarizes the results of this calculation:

HMR 51 PMP values are outdated. This calculation provided updated PMP values to replace HMR 51 PMP values using current storm data and state-of-the-science meteorological techniques and understanding.

No previous cool-season PMP values were developed by the NWS for this basin. This calculation explicitly derived cool-season PMP values at standard area sizes and durations following the standard storm based approach.

No MCCs were evaluated for PMP development. Therefore, PMP depths derived for areas less than 500-square miles and at durations less than 24-hours are for general storms only. These values may be less than would have been determined if MCCs were included in the calculation.

The most recent storm used to derive PMP values in HMR 51 occurred in 1972 (Attachment, Reference 1) and the most recent storm in HMR 52 occurred in 1973 (Table 21, Reference 2). This calculation updated the storm database to include storms through 2014.

HMR 51 and HMR 52 did not use computer based technologies in the storm analyses procedures. This calculation used computer technology and GIS to more accurately analyze storm rainfall patterns and implement the spatially distributed PMP values.

HMR 51 and HMR 52 did not have weather radar to help spatially distribute rainfall among rain gauge locations. SPAS storm analyses incorporates this information when available to provide the most advanced spatial representation of rainfall storm patterns possible.

Understanding of meteorological processes, interactions, and storm patterns have advanced greatly since the publication of HMR 51. Satellite and radar technology have greatly added to the understanding of storm patterns over the last 40 years. This calculation incorporated the state-of-the-science understanding and technology associated with analyzing extreme rainfall events.

Storm based analysis of expected meteorological conditions associated with rain-on-snow scenarios were not developed in HMR 51 or HMR 52. This calculation explicitly evaluated meteorological parameters that would reasonably be expected to occur during a cool-season PMP event.

The final results of this analysis are the following: (1) the all-season PMP depths (Table 9), (2) the cool-season PMP depths (Table 10), and (3) LIP depths (Table 7).

NF-3.5-2B Page 70 of 71

CALCULATION CONTINUATION SHEET Client/Dept. Xcel -Monticello Record No. 180999.51.1008 Project Monticello Nuclear Generating Plant Flood Hazard Analysis Project No. 180999 Calculation No. 180999.51.1008 File No. 180999.51.1000 Calculation Title Site Specific PMP and Ancillary Meteorological Analysis Rev. 1 7.0 Attachments -All-Season Short Storm List Data" (80 pages) - Cool-Season Short Storm List Data " (37 pages) -Local Intense Precipitation Short Storm List Data" (894 pages) - 100-year Return Frequency Average Dew Point Climatology Maps Used in the Storm Maximization and Transposition Calculations (36 pages) - "Procedure for using Dew Point Temperatures for Storm Maximization and Transposition (5 pages) - Procedure for Deriving PMP Values from Storm Depth-Area-Duration Analyses" (6 pages) - Depth-Area and Depth-Duration Curves (13 pages)

NF-3.5-2B Page 71 of 71

180999.51.1008 Revision 1 Attachment 1 Page 1 of 80 ATTACHMENT 1: All-Season Short Storm List Data Table 1: List of storms used in the all-season PMP development

180999.51.1008 Revision 1 Attachment 1 Page 2 of 80 Table 2: Storm spreadsheet for Aurora College, IL July 1996

180999.51.1008 Revision 1 Attachment 1 Page 3 of 80 Attachment 1 Figure 1: Moisture inflow map for Aurora College, IL July 1996 Table 3: Depth-area-duration values for Aurora College, IL July 1996

180999.51.1008 Revision 1 Attachment 1 Page 4 of 80 Figure 2: Depth-area-duration chart for Aurora College, IL July 1996 Attachment 1 Figure 3: Mass curve chart for Aurora College, IL July 1996

180999.51.1008 Revision 1 Attachment 1 Page 5 of 80 Figure 4: Total storm isohyetal analysis for Aurora College, IL July 1996

180999.51.1008 Revision 1 Attachment 1 Page 6 of 80 Table 4: Storm spreadsheet for Big Rapids, MI September 1986

180999.51.1008 Revision 1 Attachment 1 Page 7 of 80 Attachment 1 Figure 5: Moisture inflow map for Big Rapids, MI September 1986 Table 5: Depth-area-duration values for Big Rapids, MI September 1986

180999.51.1008 Revision 1 Attachment 1 Page 8 of 80 Figure 6: Depth-area-duration chart for Big Rapids, MI September 1986

180999.51.1008 Revision 1 Attachment 1 Page 9 of 80 Figure 7: Mass curve chart for Big Rapids, MI September 1986

180999.51.1008 Revision 1 Attachment 1 Page 10 of 80 Figure 8: Total storm isohyetal analysis for Big Rapids, MI September 1986

180999.51.1008 Revision 1 Attachment 1 Page 11 of 80 Table 6: Storm spreadsheet for Cole Camp, MO August 1946

180999.51.1008 Revision 1 Attachment 1 Page 12 of 80 Figure 9: Moisture inflow map for Cole Camp, MO August 1946

180999.51.1008 Revision 1 Attachment 1 Page 13 of 80 Table 7: Depth-area-duration values for Cole Camp, MO August 1946

180999.51.1008 Revision 1 Attachment 1 Page 14 of 80 Figure 10 and Attachment 1 Figure 11: Isohyetal map and Mass curve chart for Cole Camp, MO August 1946

180999.51.1008 Revision 1 Attachment 1 Page 15 of 80 Table 8: Storm spreadsheet for Collinsville, IL August 1946

180999.51.1008 Revision 1 Attachment 1 Page 16 of 80 Figure 12: Moisture inflow map for Collinsville, IL August 1946

180999.51.1008 Revision 1 Attachment 1 Page 17 of 80 Table 9: Depth-area-duration values for Collinsville, IL August 1946

180999.51.1008 Revision 1 Attachment 1 Page 18 of 80 Figure 13 and Attachment 1 Figure 14: Isohyetal map and Mass curve chart for Collinsville, IL August 1946

180999.51.1008 Revision 1 Attachment 1 Page 19 of 80 Table 10: Storm spreadsheet for Dubuque, IA July 2011

180999.51.1008 Revision 1 Attachment 1 Page 20 of 80 Figure 15: Moisture inflow map for Dubuque, IA July 2011

180999.51.1008 Revision 1 Attachment 1 Page 21 of 80 Table 11: Depth-area-duration values for Dubuque, IA July 2011

180999.51.1008 Revision 1 Attachment 1 Page 22 of 80 Figure 16: Depth-area-duration chart for Dubuque, IA July 2011

180999.51.1008 Revision 1 Attachment 1 Page 23 of 80 Figure 17: Mass curve chart for Dubuque, IA July 2011

180999.51.1008 Revision 1 Attachment 1 Page 24 of 80 Figure 18: Total storm isohyetal analysis for Dubuque, IA July 2011

180999.51.1008 Revision 1 Attachment 1 Page 25 of 80 Table 12: Storm spreadsheet for Duluth, MN June 2012

180999.51.1008 Revision 1 Attachment 1 Page 26 of 80 Figure 19: Moisture inflow map for Duluth, MN June 2012

180999.51.1008 Revision 1 Attachment 1 Page 27 of 80 Table 13: Depth-area-duration values for Duluth, MN June 2012

180999.51.1008 Revision 1 Attachment 1 Page 28 of 80 Figure 20: Depth-area-duration chart for Duluth, MN June 2012

180999.51.1008 Revision 1 Attachment 1 Page 29 of 80 Figure 21: Mass curve chart for Duluth, MN June 2012

180999.51.1008 Revision 1 Attachment 1 Page 30 of 80 Figure 22: Total storm isohyetal analysis for Duluth, MN June 2012

180999.51.1008 Revision 1 Attachment 1 Page 31 of 80 Table 14: Storm spreadsheet for Edgerton, MO July 1965

180999.51.1008 Revision 1 Attachment 1 Page 32 of 80 Figure 23: Moisture inflow map for Edgerton, MO July 1965

180999.51.1008 Revision 1 Attachment 1 Page 33 of 80 Table 15: Depth-area-duration values for Edgerton, MO July 1965

180999.51.1008 Revision 1 Attachment 1 Page 34 of 80 Figure 24: Depth-area-duration chart for Edgerton, MO July 1965 Attachment 1 Figure 25: Mass curve chart for Edgerton, MO July 1965

180999.51.1008 Revision 1 Attachment 1 Page 35 of 80 Figure 26: Total storm isohyetal analysis for Edgerton, MO July 1965

180999.51.1008 Revision 1 Attachment 1 Page 36 of 80 Table 16: Storm spreadsheet for Hayward, WI August 1941

180999.51.1008 Revision 1 Attachment 1 Page 37 of 80 Figure 27: Moisture inflow map for Hayward, WI August 1941

180999.51.1008 Revision 1 Attachment 1 Page 38 of 80 Table 17: Depth-area-duration values for Hayward, WI August 1941

180999.51.1008 Revision 1 Attachment 1 Page 39 of 80 Figure 28 and Attachment 1 Figure 29: Isohyetal map and Mass curve chart for Hayward, WI August 1941

180999.51.1008 Revision 1 Attachment 1 Page 40 of 80 Table 18: Storm spreadsheet for Hokah, MN, August 2007

180999.51.1008 Revision 1 Attachment 1 Page 41 of 80 Figure 30: Moisture inflow map for Hokah, MN, August 2007

180999.51.1008 Revision 1 Attachment 1 Page 42 of 80 Table 19: Depth-area-duration values for Hokah, MN, August 2007

180999.51.1008 Revision 1 Attachment 1 Page 43 of 80 Figure 31: Depth-area-duration chart for Hokah, MN, August 2007

180999.51.1008 Revision 1 Attachment 1 Page 44 of 80 Figure 32: Mass curve chart for Hokah, MN, August 2007

180999.51.1008 Revision 1 Attachment 1 Page 45 of 80 Figure 33: Total storm isohyetal analysis for Hokah, MN, August 2007

180999.51.1008 Revision 1 Attachment 1 Page 46 of 80 Table 20: Storm spreadsheet for Ida Grove, IA August 1962

180999.51.1008 Revision 1 Attachment 1 Page 47 of 80 Figure 34: Moisture inflow map for Ida Grove, IA August 1962

180999.51.1008 Revision 1 Attachment 1 Page 48 of 80 Figure 35 and Attachment 1 Table 21: Total storm isohyetal analysis and Depth-area-duration values for Ida Grove, IA August 1962

180999.51.1008 Revision 1 Attachment 1 Page 49 of 80 Table 22: Storm spreadsheet for Ironwood, MI July 1909

180999.51.1008 Revision 1 Attachment 1 Page 50 of 80 Figure 36: Moisture inflow map for Ironwood, MI July 1909

180999.51.1008 Revision 1 Attachment 1 Page 51 of 80 Table 23: Depth-area-duration values for Ironwood, MI July 1909

180999.51.1008 Revision 1 Attachment 1 Page 52 of 80 Figure 37 and Attachment 1 Figure 38: Isohyetal map and Mass curve chart for Ironwood, MI July 1909

180999.51.1008 Revision 1 Attachment 1 Page 53 of 80 Table 24: Storm spreadsheet for Lambert, MN July 1897

180999.51.1008 Revision 1 Attachment 1 Page 54 of 80 Figure 39: Moisture inflow map for Lambert, MN July 1897

180999.51.1008 Revision 1 Attachment 1 Page 55 of 80 Table 25: Depth-area-duration values for Lambert, MN July 1897

180999.51.1008 Revision 1 Attachment 1 Page 56 of 80 Figure 40 and Attachment 1 Figure 41: Isohyetal map and Mass curve chart for Lambert, MN July 1897

180999.51.1008 Revision 1 Attachment 1 Page 57 of 80 Table 26: Storm spreadsheet for Medford, WI June 1905

180999.51.1008 Revision 1 Attachment 1 Page 58 of 80 Figure 42: Moisture inflow map for Medford, WI June 1905

180999.51.1008 Revision 1 Attachment 1 Page 59 of 80 Table 27: Depth-area-duration values for Medford, WI June 1905

180999.51.1008 Revision 1 Attachment 1 Page 60 of 80 Figure 43 and Attachment 1 Figure 44: Isohyetal map and Mass curve chart for Medford, WI June 1905

180999.51.1008 Revision 1 Attachment 1 Page 61 of 80 Table 28: Storm spreadsheet for Prague, NE August 1959

180999.51.1008 Revision 1 Attachment 1 Page 62 of 80 Figure 45: Moisture inflow map for Prague, NE August 1959

180999.51.1008 Revision 1 Attachment 1 Page 63 of 80 Table 29 and Attachment 1 Figure 46: Depth-area-duration values and Depth-area-duration chart for Prague, NE August 1959

180999.51.1008 Revision 1 Attachment 1 Page 64 of 80 Figure 47: Mass curve chart for Prague, NE August 1959

180999.51.1008 Revision 1 Attachment 1 Page 65 of 80 Figure 48: Total storm isohyetal analysis for Prague, NE August 1959

180999.51.1008 Revision 1 Attachment 1 Page 66 of 80 Table 30: Storm spreadsheet for Warroad, MN June 2002

180999.51.1008 Revision 1 Attachment 1 Page 67 of 80 Figure 49: Moisture inflow map for Warroad, MN June 2002

180999.51.1008 Revision 1 Attachment 1 Page 68 of 80 Table 31: Depth-area-duration values for Warroad, MN June 2002

180999.51.1008 Revision 1 Attachment 1 Page 69 of 80 Figure 50: Depth-area-duration chart for Warroad, MN June 2002

180999.51.1008 Revision 1 Attachment 1 Page 70 of 80 Figure 51: Mass curve chart for Warroad, MN June 2002

180999.51.1008 Revision 1 Attachment 1 Page 71 of 80 Figure 52: Total storm isohyetal analysis for Warroad, MN June 2002

180999.51.1008 Revision 1 Attachment 1 Page 72 of 80 Table 32: Storm spreadsheet for Woodburn, IA August 1903

180999.51.1008 Revision 1 Attachment 1 Page 73 of 80 Figure 53: Moisture inflow map for Woodburn, IA August 1903

180999.51.1008 Revision 1 Attachment 1 Page 74 of 80 Table 33: Depth-area-duration values for Woodburn, IA August 1903

180999.51.1008 Revision 1 Attachment 1 Page 75 of 80 Figure 54 and Attachment 1 Figure 55: Isohyetal map and Mass curve chart for Woodburn, IA August 1903

180999.51.1008 Revision 1 Attachment 1 Page 76 of 80 Table 34: Storm spreadsheet for Wooster, OH July 1969

180999.51.1008 Revision 1 Attachment 1 Page 77 of 80 Attachment 1 Figure 56: Moisture inflow map for Wooster, OH July 1969 Table 35: Depth-area-duration values for Wooster, OH July 1969

180999.51.1008 Revision 1 Attachment 1 Page 78 of 80 Figure 57: Depth-area-duration chart for Wooster, OH July 1969

180999.51.1008 Revision 1 Attachment 1 Page 79 of 80 Figure 58: Mass curve chart for Wooster, OH July 1969

180999.51.1008 Revision 1 Attachment 1 Page 80 of 80 Figure 59: Total storm isohyetal analysis for Wooster, OH July 1969

180999.51.1008 Revision 1 Attachment 2 Page 1 of 37 ATTACHMENT 2: Cool-Season Short Storm List Data Table 1: List of storm used in the cool-season PMP development

180999.51.1008 Revision 1 Attachment 2 Page 2 of 37 Table 2: Storm spreadsheet for Ashland, WI April 2001

180999.51.1008 Revision 1 Attachment 2 Page 3 of 37 Figure 1: Moisture inflow map for Ashland, WI April 2001

180999.51.1008 Revision 1 Attachment 2 Page 4 of 37 Table 3: Depth-area-duration values for Ashland, WI April 2001

180999.51.1008 Revision 1 Attachment 2 Page 5 of 37 Figure 2: Depth-area-duration chart for Ashland, WI April 2001

180999.51.1008 Revision 1 Attachment 2 Page 6 of 37 Figure 3: Mass curve chart for Ashland, WI April 2001

180999.51.1008 Revision 1 Attachment 2 Page 7 of 37 Figure 4: Total storm isohyetal analysis for Ashland, WI April 2001

180999.51.1008 Revision 1 Attachment 2 Page 8 of 37 Table 4: Storm spreadsheet for Bellefontaine, OH March 1913

180999.51.1008 Revision 1 Attachment 2 Page 9 of 37 Figure 5: Moisture inflow map for Bellefontaine, OH March 1913

180999.51.1008 Revision 1 Attachment 2 Page 10 of 37 Table 5: Depth-area-duration values for Bellefontaine, OH March 1913

180999.51.1008 Revision 1 Attachment 2 Page 11 of 37 Figure 6 and Attachment 2 Figure 7: Isohyetal map and Mass curve chart for Bellefontaine, OH March 1913

180999.51.1008 Revision 1 Attachment 2 Page 12 of 37 Table 6: Storm spreadsheet for Conception, MO May 1919

180999.51.1008 Revision 1 Attachment 2 Page 13 of 37 Figure 8: Moisture inflow map for Conception, MO May 1919

180999.51.1008 Revision 1 Attachment 2 Page 14 of 37 Table 7: Depth-area-duration values for Conception, MO May 1919

180999.51.1008 Revision 1 Attachment 2 Page 15 of 37 Figure 9 and Attachment 2 Figure 10: Isohyetal map and Mass curve chart for Conception, MO May 1919

180999.51.1008 Revision 1 Attachment 2 Page 16 of 37 Table 8: Storm spreadsheet for Lansing, MI April 1975

180999.51.1008 Revision 1 Attachment 2 Page 17 of 37 Figure 11: Moisture inflow map for Lansing, MI April 1975

180999.51.1008 Revision 1 Attachment 2 Page 18 of 37 Figure 12 and Attachment 2 Table 9: Total storm isohyetal analysis and Depth-area-duration values for Lansing, MI April 1975

180999.51.1008 Revision 1 Attachment 2 Page 19 of 37 Table 10: Storm spreadsheet for Louisville, KY February 1997

180999.51.1008 Revision 1 Attachment 2 Page 20 of 37 Figure 13: Moisture inflow map for Louisville, KY February 1997

180999.51.1008 Revision 1 Attachment 2 Page 21 of 37 Table 11: Depth-area-duration values for Louisville, KY February 1997

180999.51.1008 Revision 1 Attachment 2 Page 22 of 37 Figure 14: Depth-area-duration chart for Louisville, KY February 1997

180999.51.1008 Revision 1 Attachment 2 Page 23 of 37 Figure 15: Mass curve chart for Louisville, KY February 1997

180999.51.1008 Revision 1 Attachment 2 Page 24 of 37 Figure 16: Total storm isohyetal analysis for Louisville, KY February 1997

180999.51.1008 Revision 1 Attachment 2 Page 25 of 37 Table 12: Storm spreadsheet for Madisonville, KY March 1964

180999.51.1008 Revision 1 Attachment 2 Page 26 of 37 Figure 17: Moisture inflow map for Madisonville, KY March 1964

180999.51.1008 Revision 1 Attachment 2 Page 27 of 37 Table 13: Depth-area-duration values for Madisonville, KY March 1964

180999.51.1008 Revision 1 Attachment 2 Page 28 of 37 Figure 18: Depth-area-duration chart for Madisonville, KY March 1964 Attachment 2 Figure 19: Mass curve chart for Madisonville, KY March 1964

180999.51.1008 Revision 1 Attachment 2 Page 29 of 37 Figure 20: Total storm isohyetal analysis for Madisonville, KY March 1964

180999.51.1008 Revision 1 Attachment 2 Page 30 of 37 Table 14: Storm spreadsheet for Oconto, WI April 1919

180999.51.1008 Revision 1 Attachment 2 Page 31 of 37 Figure 21: Moisture inflow map for Oconto, WI April 1919

180999.51.1008 Revision 1 Attachment 2 Page 32 of 37 Table 15: Depth-area-duration values for Oconto, WI April 1919

180999.51.1008 Revision 1 Attachment 2 Page 33 of 37 Figure 22 and Attachment 2 Figure 23: Isohyetal map and Mass curve chart for Oconto, WI April 1919

180999.51.1008 Revision 1 Attachment 2 Page 34 of 37 Table 16: Storm spreadsheet for Tuscumbia, MO March 1927

180999.51.1008 Revision 1 Attachment 2 Page 35 of 37 Figure 24: Moisture inflow map for Tuscumbia, MO March 1927

180999.51.1008 Revision 1 Attachment 2 Page 36 of 37 Table 17: Depth-area-duration values for Tuscumbia, MO March 1927

180999.51.1008 Revision 1 Attachment 2 Page 37 of 37 Figure 25 and Attachment 2 Figure 26: Isohyetal map and Mass curve chart for Tuscumbia, MO March 1927

180999.51.1008 Revision 1 Attachment 3 ATTACHMENT 3: Local Intense Precipitation Short Storm List Data Page 1 of 84 Table 1: List of storm used in the Local Intense Precipitation PMP development

180999.51.1008 Revision 1 Attachment 3 Page 2 of 84 Table 2: Storm spreadsheet for Aurora College, IL July 1996

180999.51.1008 Revision 1 Attachment 3 Page 3 of 84 Attachment 3 Figure 1: Moisture inflow map for Aurora College, IL July 1996 Table 3: Depth-area-duration values for Aurora College, IL July 1996

180999.51.1008 Revision 1 Attachment 3 Page 4 of 84 Figure 2: Depth-area-duration chart for Aurora College, IL July 1996 Attachment 3 Figure 3: Mass curve chart for Aurora College, IL July 1996

180999.51.1008 Revision 1 Attachment 3 Page 5 of 84 Figure 4: Total storm isohyetal analysis for Aurora College, IL July 1996

180999.51.1008 Revision 1 Attachment 3 Page 6 of 84 Table 4: Storm spreadsheet for Beaulieu, MN July 1909

180999.51.1008 Revision 1 Attachment 3 Page 7 of 84 Figure 5: Moisture inflow map for Beaulieu, MN July 1909

180999.51.1008 Revision 1 Attachment 3 Page 8 of 84 Table 5: Depth-area-duration values for Beaulieu, MN July 1909

180999.51.1008 Revision 1 Attachment 3 Page 9 of 84 Figure 6 and Attachment 3 Figure 7: Isohyetal map and Mass curve chart for Beaulieu, MN July 1909

180999.51.1008 Revision 1 Attachment 3 Page 10 of 84 Table 6: Storm spreadsheet for Boyden, IA September 1926

180999.51.1008 Revision 1 Attachment 3 Page 11 of 84 Figure 8: Moisture inflow map for Boyden, IA September 1926

180999.51.1008 Revision 1 Attachment 3 Page 12 of 84 Table 7: Depth-area-duration values for Boyden, IA September 1926

180999.51.1008 Revision 1 Attachment 3 Page 13 of 84 Figure 9 and Attachment 3 Figure 10: Isohyetal map and Mass curve chart for Boyden, IA September 1926

180999.51.1008 Revision 1 Attachment 3 Page 14 of 84 Table 8: Storm spreadsheet for Cooper, MI August 1914

180999.51.1008 Revision 1 Attachment 3 Page 15 of 84 Figure 11: Moisture inflow map for Cooper, MI August 1914

180999.51.1008 Revision 1 Attachment 3 Page 16 of 84 Table 9: Depth-area-duration values for Cooper, MI August 1914

180999.51.1008 Revision 1 Attachment 3 Page 17 of 84 Figure 12 and Attachment 3 Figure 13: Isohyetal map and Mass curve chart for Cooper, MI August 1914

180999.51.1008 Revision 1 Attachment 3 Page 18 of 84 Table 10: Storm spreadsheet for David City, NE June 1963

180999.51.1008 Revision 1 Attachment 3 Page 19 of 84 Attachment 3 Figure 14: Moisture inflow map for David City, NE June 1963 Table 11: Depth-area-duration values for David City, NE June 1963

180999.51.1008 Revision 1 Attachment 3 Page 20 of 84 Figure 15: Depth-area-duration chart for David City, NE June 1963 Attachment 3 Figure 16: Mass curve chart for David City, NE June 1963

180999.51.1008 Revision 1 Attachment 3 Page 21 of 84 Figure 17: Total storm isohyetal analysis for David City, NE June 1963

180999.51.1008 Revision 1 Attachment 3 Page 22 of 84 Table 12: Storm spreadsheet for Dubuque, IA July 2011

180999.51.1008 Revision 1 Attachment 3 Page 23 of 84 Attachment 3 Figure 18: Moisture inflow map for Dubuque, IA July 2011 Table 13: Depth-area-duration values for Dubuque, IA July 2011

180999.51.1008 Revision 1 Attachment 3 Page 24 of 84 Figure 19: Depth-area-duration chart for Dubuque, IA July 2011 Attachment 3 Figure 20: Mass curve chart for Dubuque, IA July 2011

180999.51.1008 Revision 1 Attachment 3 Page 25 of 84 Figure 21: Total storm isohyetal analysis for Dubuque, IA July 2011

180999.51.1008 Revision 1 Attachment 3 Page 26 of 84 Table 14: Storm spreadsheet for Dumont, IA June 1951

180999.51.1008 Revision 1 Attachment 3 Page 27 of 84 Figure 22: Moisture inflow map for Dumont, IA June 1951

180999.51.1008 Revision 1 Attachment 3 Page 28 of 84 Table 15: Depth-area-duration values for Dumont, IA June 1951

180999.51.1008 Revision 1 Attachment 3 Page 29 of 84 Figure 23 and Attachment 3 Figure 24: Isohyetal map and Mass curve chart for Dumont, IA June 1951

180999.51.1008 Revision 1 Attachment 3 Page 30 of 84 Table 16: Storm spreadsheet for Enid, OK October 1973

180999.51.1008 Revision 1 Attachment 3 Page 31 of 84 Attachment 3 Figure 25: Moisture inflow map for Enid, OK October 1973 Table 17: Depth-area-duration values for Enid, OK October 1973

180999.51.1008 Revision 1 Attachment 3 Page 32 of 84 Figure 26: Depth-area-duration chart for Enid, OK October 1973 Attachment 3 Figure 27: Mass curve chart for Enid, OK October 1973

180999.51.1008 Revision 1 Attachment 3 Page 33 of 84 Figure 28: Total storm isohyetal analysis for Enid, OK October 1973

180999.51.1008 Revision 1 Attachment 3 Page 34 of 84 Table 18: Storm spreadsheet for Fall River, KS June 2007

180999.51.1008 Revision 1 Attachment 3 Page 35 of 84 Figure 29: Moisture inflow map for Fall River, KS June 2007

180999.51.1008 Revision 1 Attachment 3 Page 36 of 84 Table 19: Depth-area-duration values for Fall River, KS June 2007

180999.51.1008 Revision 1 Attachment 3 Page 37 of 84 Figure 30: Depth-area-duration chart for Fall River, KS June 2007

180999.51.1008 Revision 1 Attachment 3 Page 38 of 84 Figure 31: Mass curve chart for Fall River, KS June 2007

180999.51.1008 Revision 1 Attachment 3 Page 39 of 84 Figure 32: Total storm isohyetal analysis for Fall River, KS June 2007

180999.51.1008 Revision 1 Attachment 3 Page 40 of 84 Table 20: Storm spreadsheet for Forest City, MN June 1983

180999.51.1008 Revision 1 Attachment 3 Page 41 of 84 Figure 33: Moisture inflow map for Forest City, MN June 1983

180999.51.1008 Revision 1 Attachment 3 Page 42 of 84 Table 21 and Attachment 3 Figure 34: Depth-area-duration values and Depth-area-duration chart for Forest City, MN June 1983

180999.51.1008 Revision 1 Attachment 3 Page 43 of 84 Figure 35: Mass curve chart for Forest City, MN June 1983

180999.51.1008 Revision 1 Attachment 3 Page 44 of 84 Figure 36: Total storm isohyetal analysis for Forest City, MN June 1983

180999.51.1008 Revision 1 Attachment 3 Page 45 of 84 Table 22: Storm spreadsheet for Grant Township, NE June 1940

180999.51.1008 Revision 1 Attachment 3 Page 46 of 84 Figure 37: Moisture inflow map for Grant Township, NE June 1940

180999.51.1008 Revision 1 Attachment 3 Page 47 of 84 Table 23: Depth-area-duration values for Grant Township, NE June 1940

180999.51.1008 Revision 1 Attachment 3 Page 48 of 84 Figure 38 and Attachment 3 Figure 39: Isohyetal map and Mass curve chart for Grant Township, NE June 1940

180999.51.1008 Revision 1 Attachment 3 Page 49 of 84 Table 24: Storm spreadsheet for Holt, MO June 1947

180999.51.1008 Revision 1 Attachment 3 Page 50 of 84 Figure 40: Moisture inflow map for Holt, MO June 1947

180999.51.1008 Revision 1 Attachment 3 Page 51 of 84 Table 25: Depth-area-duration values for Holt, MO June 1947

180999.51.1008 Revision 1 Attachment 3 Page 52 of 84 Figure 41 and Attachment 3 Figure 42: Isohyetal map and Mass curve chart for Holt, MO June 1947

180999.51.1008 Revision 1 Attachment 3 Page 53 of 84 Table 26: Storm spreadsheet for Kelso, MO August 1952

180999.51.1008 Revision 1 Attachment 3 Page 54 of 84 Figure 43: Moisture inflow map for Kelso, MO August 1952

180999.51.1008 Revision 1 Attachment 3 Page 55 of 84 Table 27: Depth-area-duration values for Kelso, MO August 1952

180999.51.1008 Revision 1 Attachment 3 Page 56 of 84 Figure 44 and Attachment 3 Figure 45: Isohyetal map and Mass curve chart for Kelso, MO August 1952

180999.51.1008 Revision 1 Attachment 3 Page 57 of 84 Table 28: Storm spreadsheet for Larrabee, IA June 1891

180999.51.1008 Revision 1 Attachment 3 Page 58 of 84 Figure 46: Moisture inflow map for Larrabee, IA June 1891

180999.51.1008 Revision 1 Attachment 3 Page 59 of 84 Table 29: Depth-area-duration values for Larrabee, IA June 1891

180999.51.1008 Revision 1 Attachment 3 Page 60 of 84 Figure 47 and Attachment 3 Figure 48: Isohyetal map and Mass curve chart for Larrabee, IA June 1891

180999.51.1008 Revision 1 Attachment 3 Page 61 of 84 Table 30: Storm spreadsheet for Minneapolis, MN July 1987

180999.51.1008 Revision 1 Attachment 3 Page 62 of 84 Attachment 3 Figure 49: Moisture inflow map for Minneapolis, MN July 1987 Table 31: Depth-area-duration values for Minneapolis, MN July 1987

180999.51.1008 Revision 1 Attachment 3 Page 63 of 84 Figure 50: Depth-area-duration chart for Minneapolis, MN July 1987 Attachment 3 Figure 51: Mass curve chart for Minneapolis, MN July 1987

180999.51.1008 Revision 1 Attachment 3 Page 64 of 84 Figure 52: Total storm isohyetal analysis for Minneapolis, MN July 1987

180999.51.1008 Revision 1 Attachment 3 Page 65 of 84 Table 32: Storm spreadsheet for Mounds, OK May 1943

180999.51.1008 Revision 1 Attachment 3 Page 66 of 84 Figure 53: Moisture inflow map for Mounds, OK May 1943

180999.51.1008 Revision 1 Attachment 3 Page 67 of 84 Table 33: Depth-area-duration values for Mounds, OK May 1943

180999.51.1008 Revision 1 Attachment 3 Page 68 of 84 Figure 54 and Attachment 3 Figure 55: Isohyetal map and Mass curve chart for Mounds, OK May 1943

180999.51.1008 Revision 1 Attachment 3 Page 69 of 84 Table 34: Storm spreadsheet for Neosho Falls, KS September 1926

180999.51.1008 Revision 1 Attachment 3 Page 70 of 84 Figure 56: Moisture inflow map for Neosho Falls, KS September 1926

180999.51.1008 Revision 1 Attachment 3 Page 71 of 84 Table 35: Depth-area-duration values for Neosho Falls, KS September 1926

180999.51.1008 Revision 1 Attachment 3 Page 72 of 84 Figure 57 and Attachment 3 Figure 58: Isohyetal map and Mass curve chart for Neosho Falls, KS September 1926

180999.51.1008 Revision 1 Attachment 3 Page 73 of 84 Table 36: Storm spreadsheet for Stanton, NE June 1944

180999.51.1008 Revision 1 Attachment 3 Page 74 of 84 Figure 59: Moisture inflow map for Stanton, NE June 1944

180999.51.1008 Revision 1 Attachment 3 Page 75 of 84 Table 37: Depth-area-duration values for Stanton, NE June 1944

180999.51.1008 Revision 1 Attachment 3 Page 76 of 84 Figure 60 and Attachment 3 Figure 61: Isohyetal map and Mass curve chart for Stanton, NE June 1944

180999.51.1008 Revision 1 Attachment 3 Page 77 of 84 Table 38: Storm spreadsheet for Woodburn, IA August 1903

180999.51.1008 Revision 1 Attachment 3 Page 78 of 84 Figure 62: Moisture inflow map for Woodburn, IA August 1903

180999.51.1008 Revision 1 Attachment 3 Page 79 of 84 Table 39: Depth-area-duration values for Woodburn, IA August 1903

180999.51.1008 Revision 1 Attachment 3 Page 80 of 84 Figure 63 and Attachment 3 Figure 64: Isohyetal map and Mass curve chart for Woodburn, IA August 1903

180999.51.1008 Revision 1 Attachment 3 Page 81 of 84 Table 40: Storm spreadsheet for Wooster, OH July 1969

180999.51.1008 Revision 1 Attachment 3 Page 82 of 84 Attachment 3 Figure 65: Moisture inflow map for Wooster, OH July 1969 Table 41: Depth-area-duration values for Wooster, OH July 1969

180999.51.1008 Revision 1 Attachment 3 Page 83 of 84 Figure 66: Depth-area-duration chart for Wooster, OH July 1969 Attachment 3 Figure 67: Mass curve chart for Wooster, OH July 1969

180999.51.1008 Revision 1 Attachment 3 Page 84 of 84 Figure 68: Total storm isohyetal analysis for Wooster, OH July 1969

180999.51.1008 Revision 1 Attachment 4 Page 1 of 36 ATTACHMENT 4: 100-year Return Frequency Average Dew Point Climatology Maps Used in the Storm Maximization and Transposition Calculations Attachment 4 Figure 1: January 6-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 2 of 36 Figure 2: February 6-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 3 of 36 Figure 3: March 6-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 4 of 36 Figure 4: April 6-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 5 of 36 Figure 5: May 6-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 6 of 36 Figure 6: June 6-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 7 of 36 Figure 7: July 6-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 8 of 36 Figure 8: August 6-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 9 of 36 Figure 9: September 6-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 10 of 36 Figure 10: October 6-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 11 of 36 Figure 11: November 6-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 12 of 36 Figure 12: December 6-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 13 of 36 Figure 13: January 12-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 14 of 36 Figure 14: February 12-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 15 of 36 Figure 15: March 12-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 16 of 36 Figure 16: April 12-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 17 of 36 Figure 17: May 12-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 18 of 36 Figure 18: June 12-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 19 of 36 Figure 19: July 12-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 20 of 36 Figure 20: August 12-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 21 of 36 Figure 21: September 12-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 22 of 36 Figure 22: October 12-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 23 of 36 Figure 23: November 12-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 24 of 36 Figure 24: December 12-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 25 of 36 Figure 25: January 24-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 26 of 36 Figure 26: February 24-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 27 of 36 Figure 27: March 24-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 28 of 36 Figure 28: April 24-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 29 of 36 Figure 29: May 24-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 30 of 36 Figure 30: June 24-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 31 of 36 Figure 31: July 24-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 32 of 36 Figure 32: August 24-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 33 of 36 Figure 33: September 24-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 34 of 36 Figure 34: October 24-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 35 of 36 Figure 35: November 24-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 4 Page 36 of 36 Figure 36: December 24-hour 100-year maximum dew point climatology

180999.51.1008 Revision 1 Attachment 5 Page 1 of 5 ATTACHMENT 5: Procedure for using Dew Point Temperatures for Storm Maximization and Transposition Maximum dew point temperatures (hereafter referred to as dew points) have historically been used for two primary purposes in the PMP computation process:

1. Increase the observed rainfall amounts to a maximum value based on a potential increase in atmospheric moisture available to the storm.

2. Adjust the available atmospheric moisture to account for any increases or decreases associated with the maximized storm potentially occurring at another location within the transposition limits for that storm.

HMR and WMO procedures for storm maximization use a representative storm dew point as the parameter to represent available moisture to a storm. Prior to the mid-1980s, maps of maximum dew point values from the Climatic Atlas of the United States, Environmental Data Services, Department of Commerce, were the source for maximum dew point values. HMR 55 published in 1984 updated maximum dew point values for a portion of the United States from the Continental Divide eastward into the central plains.

A regional PMP study for Michigan and Wisconsin produced return frequency maps using the L-moments method. The Review Committee for that study included representatives from NWS, FERC, Bureau of Reclamation, and others. They agreed that the 50-year return frequency values were appropriate for use in PMP calculations. HMR 57 was published in 1994 and HMR 59 in 1999. These latest NWS publications also update the maximum dew point climatology but use maximum observed dew points instead of return frequency values. For this study, the 100-year return frequency dew point climatology maps were appropriate because this added a layer of conservatism and the extra 17 years of data available since the EPRI and Nebraska studies allow the 100-year return frequency to be more reliable. Storm precipitation amounts are maximized using the ratio of precipitable water for the maximum observed dew point to precipitable water for the storm representative dew point, assuming a vertically saturated atmosphere.

This procedure was followed in this study using the updated maximum dew point climatology developed in Appendix 4.

The procedure for determining a storm representative dew point begins with the determination of the inflow wind vector (direction and magnitude) for the air mass that contains the atmospheric moisture available to the storm. Beginning and ending times of the rainfall event at locations of the most extreme rainfall amounts are determined using rainfall mass curves from those locations.

The storm inflow wind vector is determined using available wind data. The inflow wind vector has historically been determined using winds reported by weather stations, together with upper air winds, when available. Recently, re-analyzed weather and weather model data representing various atmospheric parameters including wind direction and speed in the atmosphere have become available for use from the HYSPLIT trajectory model and the North American Reanalysis Project. These analyses are

180999.51.1008 Revision 1 Attachment 5 Page 2 of 5 available back to 1948. Use of these wind fields in the lower portion of the atmosphere provides much improved reliability in the determination of the storm inflow wind vectors. The program is available through an online interface through the Air Resources Laboratory section of NOAA. Users are able to enter in specific parameters that then produce a trajectory from a starting point going backwards (or forwards) for a specified amount of time. Users can define variables such as the starting point (using latitude and longitude or a map interface), the date and time to start the trajectory, the length of time to run the trajectory, and the pressure level at which to delineate the inflow vector. Figure 1 shows an example inflow vectors generated by HYSPLIT at three levels: 700mb, 850mb, and surface. The data generated from the HYSPLIT runs is then used in conjunction with standard methods to help delineate the source region of the air mass responsible for the storm precipitation. Also, this serves as another tool to determine from which weather stations to derive hourly dew point data for storm representative dew point analysis.

180999.51.1008 Revision 1 Attachment 5 Page 3 of 5 Figure 1: HYSPLIT trajectory model results for Ashland, WI April 2001 The inflow wind vector is followed upwind until a location is reached that is outside of the storm rainfall. The nearest weather stations that report dew point values are identified. At least two stations are desired but a single station with reliable dew points observations can be used. The time period used to identify the appropriate dew point values is determined by computing the time required for the air mass to be transported from the location of the weather station to the location of maximum rainfall.

180999.51.1008 Revision 1 Attachment 5 Page 4 of 5 The start time of the extreme rainfall is then adjusted back in time to account for transit time from the dew point observing station to the maximum rainfall location.

For example, consider the following case:

1. Rainfall begins at 11:00am and ends at 6:00pm the following day at the location of maximum rainfall,

2. The storm representative dew point location (the location of the weather stations observing the dew points) is 100 miles from the maximum rainfall location in the direction of the inflow wind vector, and

3. The inflow wind speed is 20 mph.

The transit time for the air mass from the weather stations to the maximum rainfall location is five hours (100 miles divided by 20 mph). The time to begin using the dew point observations is five hours before the rainfall began (11:00am minus 5 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months =

6:00am) and the time to stop using the dew point observations is five hours before the rainfall ended (6:00pm minus 5 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months = 1:00pm the following day). Dew point observations taken between these times are used to determine the storm representative average 24-hour 1,000mb dew point value. The storm representative dew point location can come from a single location if only one station is used or from a location between the reporting weather stations if more than one station is used. The vector connecting this location and the location of maximum rainfall becomes the wind inflow vector used for storm transpositioning.

The storm representative dew point determined from the weather dew point observations needs to be corrected to the 1000mb level. The elevation of the storm representative dew point location is used in this correction. The correction factor of 2.4oF per 1,000 feet of elevation is used. This is the same correction factor used in the Climatic Atlas of the United States. For example, a storm representative dew point of 72oF at a station location with an elevation of 800 feet above sea level is corrected with a factor of 800 X 2.7 /1,000 = 2.2oF. The dew point value corrected to 1,000mb (sea level) is 72oF +

2.2oF = 74oF after rounding.

The procedure that computes the in-place maximized rainfall for a storm provides an estimate of the maximum amount of rainfall that could have been produced by the same storm at the same location if the maximum amount of atmospheric moisture had been available. This procedure requires that a maximum value for the storm representative dew point be determined. The maximum dew point value is selected at the same location where the storm dew point was determined using a maximum dew point climatology. The maximum dew point values must be corrected to 1,000mb. The precipitable water in the atmosphere is determined using the storm representative and maximum dew point values. Precipitable water is defined in this study as the total amount of moisture in a column of the atmosphere from sea level to 30,000 feet assuming a vertically saturated atmosphere. Values of atmospheric precipitable water are determined using the moist pseudo-adiabatic assumption, i.e. assume that for the given 1,000mb dew point value, the atmosphere holds the maximum amount of moisture

180999.51.1008 Revision 1 Attachment 5 Page 5 of 5 possible. The ratio of the precipitable water associated with the maximum 1,000mb dew point to the precipitable water associated with the 1,000mb storm representative dew point is the maximization factor.

For example, consider the following case:

1,000mb storm representative dew point: 72oF 1,000mb maximum dew point: 76oF Precipitable water associated with a 1,000mb dew point of 72oF: 2.47 Precipitable water associated with a 1,000mb dew point of 76oF: 2.99 Maximization factor: PW(76oF)/PW(72oF) = 2.99 /2.47 = 1.21 For transpositioning, the storm inflow vector (determined by connecting the storm representative dew point location with the location of maximum rainfall) is moved to the basin location being studied. The new location of the upwind end of the vector is determined. The maximum dew point associated with that location is then selected using the same maximum dew point climatology map used for in-place maximization. The transpositioning factor is the ratio of the precipitable water associated with the maximum 1,000mb dew point value at the transpositioned location to the precipitable water associated with the maximum 1,000mb dew point for the storm representative dew point location.

An example is provided.

1,000mb maximum dew point at the storm representative dew point location: 76oF 1,000mb maximum dew point at the transpositioned location: 74oF Precipitable water associated with a 1,000mb dew point of 76oF: 2.99 Precipitable water associated with a 1,000mb dew point of 74oF: 2.73 Transposition factor: PW(74oF)/PW(76oF) = 2.73 /2.99 = 0.91

180999.51.1008 Revision 1 Attachment 6 Page 1 of 6 ATTACHMENT 6: Procedure for Deriving PMP Values from Storm Depth-Area-Duration Analyses Although PMP rainfall amounts are theoretical values, there currently is no theoretical method for determining the values. The accepted procedure for determining PMP values begins with the identification of the largest identified historic observed rainfall amounts in the region and applies the following procedures:

1. Increase the rainfall amounts to some maximized value (in-place maximization),

2. Adjust the "maximized" rainfall amounts to the potential situation where the historic storm occurs over the basin being studied (transposition),

3. Adjust the "maximized transpositioned" rainfall amounts for elevation changes or intervening topographic barriers which could potentially affect the storm moisture and subsequently the rainfall amounts for the "maximized transpositioned" storm (barrier adjustment).

The procedure begins with the DAD analysis from the largest of the identified storms that have occurred over regions that are climatologically and topographically similar to the area being studied. Identification of the largest rainfall events is relatively straight forward and is accomplished by identifying the largest station rainfall amounts and correlating the dates among adjacent stations to identify the areal extent of the heavy rainfall and the storm period. The DAD for each storm is computed using isohyetal analyses for each hour during the storm and determining the largest rainfall totals for each duration of interest over each area size of interest. HMR 51 uses temporal periods of 6-, 12-, 24-, 48- and 72- hours. Standard area sizes of 10-, 200-, 1,000-, 5,000-,

10,000- and 20,000-square miles area used. Other durations and area sizes can also be used in the DAD analysis as desired.

The US Army Corps of Engineers, the Bureau of Reclamation and the National Weather Service have performed storm studies and produced DADs for many storms.

This study reviewed additional weather station data to identify extreme rainfall storms that had not been identified and studied previously. The new storms identified primarily occurred since the publication of HMR 51, but additional storms that occurred prior to HMR 51 publication were also identified. DADs that had been previously developed are used in this report. Newly identified storms are analyzed in this study, and DADs are developed for these storms. These DADs quantify the rainfall associated with each storm event, providing the largest rainfall amounts for each of the durations and area sizes used in this study.

Identification of storms that can be transpositioned to the MNGP watershed is largely based on subjective judgments. For a storm to be transpositionable, it should have occurred over a region that is meteorologically and topographically similar to the basin being studied. Storms generally should not be transpositioned across significant topographic features or into different climate regions. Therefore, it is assumed that the

180999.51.1008 Revision 1 Attachment 6 Page 2 of 6 same moisture sources and dynamics that produced these events could have produced a similar storm over the basin.

Maximization of the storm DADs involves deriving the in-place and transposition factors to adjust the observed rainfall to look like it would have occurred had the storm been located over the basin. This accounts for the three factors which could affect a particular storm as it's moved from its original location to the MNGP basin centroid; the storm could have been some amount bigger in-place had more moisture been available, the storm would have had more or less moisture available versus where it originally occurred based on it being moved toward or away from its moisture source, and the storm would have occurred at a lower or higher elevation than its original location. This follows the procedures and calculations described in Attachment E.

For this study, all computations associated with historic storms are computed at the 1,000mb level (approximately sea level). The elevation of the location where the largest rainfall was observed is used as the storm elevation. An adjustment is applied to the storm moisture to account for the elevation of the storm above sea level. For example, if the maximum rainfall occurred at an elevation of 500 feet, the total atmospheric moisture (500 to 30,000 feet) is decreased by the amount of moisture associated with the storm representative dew point between sea level and 500 feet. The adjustment factor uses precipitable water contained in the moisture maximized atmosphere above the storm elevation, i.e., the moisture contained in the entire depth of the moisture maximized atmosphere, minus the moisture contained in the moisture maximized atmosphere below the storm elevation. An adjustment was made to account for the storms elevation (either higher or lower than the basin centroid elevation) and the amount of precipitable water that would be available while taking into consideration upwind elevated barrier, more if the elevation was lower and less if the elevation was higher. This elevation adjustment factor is determined by computing the ratio of precipitable water in the moisture maximized atmosphere above the elevation to the precipitable water in the entire depth of the moisture maximized atmosphere.

The equations for the computation of the in-place maximization factor, transposition and elevation adjustment factors are as follows:

In-place maximization factor =

(storm representative maximum dew point PW - in-place storm elevation maximum dew point PW) / (storm representative dew point PW - in-place storm elevation representative dew point PW)

Transpositioned/elevation to basin factor =

(transpositioned maximum dew point PW - average basin elevation maximum dew point PW)/(storm representative maximum dew point PW - in-place storm elevation representative dew point PW)

Barrier adjustment factor =

180999.51.1008 Revision 1 Attachment 6 Page 3 of 6 (transpositioned maximum dew point or PW - moisture inflow barrier elevation maximum PW)/( transpositioned maximum dew point or PW - average basin elevation maximum dew point or PW)

Multiplication of these terms leads to a simplified computation where all the required adjustments are combined in a single equation.

Total adjustment factor =

(in-place max factor) * (transpositioned/elevation to basin factor) * (barrier adjustment factor)

The total adjustment factor modifies the storm DAD by a factor using two computed values:

1) The maximum atmospheric moisture available to a historic storm if it were to occur over the study basin. This air mass is assumed to contain the maximum amount of atmospheric moisture for the basin location and is adjusted for elevation upwind of the basin and within the basin.

2) The atmospheric moisture available for the historic storm at the location and elevation where it occurred.

The total adjustment factor is applied as a linear multiplier for all rainfall amounts in the storm DAD.

As an example, the DAD from a storm center is maximized, transpositioned/elevation adjusted to the MNGP basin centroid. The following are values for the parameters used in computing the adjustments:

Storm representative: 75.0° F In-place maximum: 76.5° F Transpositioned maximum: 75.0° F Storm elevation: 600' Average basin elevation: 1,000 Total atmospheric precipitable water for 75.0° F: 2.85" Total atmospheric precipitable water for 76.5° F: 3.07" Total atmospheric precipitable water for 75.0o F: 2.85" Adjustment for storm elevation, 1,000mb to 600' at 75.0°F: 0.15" Adjustment for storm elevation, 1,000mb to 600' at 76.5°F: 0.16" Adjustment for ave basin elevation, 1,000mb to 1,000' at 75.0°F: 0.25" Adjustment for inflow barrier elevation, 1,000mb to 1,000' at 75.0°F: 0.25" Total adjustment factor =

(in-place max factor) * (transpositioned/elevation to basin factor) * (barrier adjustment factor)

180999.51.1008 Revision 1 Attachment 6 Page 4 of 6

= ((3.07" - 0.16") / (2.85 " - 0.15")) * ((2.85" - 0.25") / (3.07" - 0.16")) * ((2.85" - 0.25")

/ (2.85" - 0.25")) = (1.08) * (0.90) * (1.00) = 0.96 To explicitly show how each adjustment factor (in-place maximization, transposition and barrier adjustment) affects the total adjustment, separate computation are provided.

In-place maximization factor Storm representative: 75.0° F In-place maximum: 76.5° F Storm atmospheric precipitable water for 75.0° F: 2.85" Maximum atmospheric precipitable water for 76.5° F: 3.07" Adjustment for storm elevation, 1,000mb to 600' at 75.0°F: 0.15" Adjustment for storm elevation, 1,000mb to 600' at 76.5°F: 0.16" In-place maximization factor =

(storm representative maximum dew point PW - in place storm elevation maximum PW)/(storm representative dew point PW - in place storm elevation maximum dew point PW)

= (3.07"- 0.16) / (2.85" - 0.15)

= 2.91 / 2.70

1.08 Transposition factor In-place maximum: 76.5° F Transpositioned maximum: 75.0° F Maximum atmospheric precipitable water for 76.5° F: 3.07 Maximum atmospheric precipitable water for 75.0° F: 2.85 Adjustment for storm elevation, 1,000mb to 600' at 76.5°F: 0.16" Adjustment for storm elevation, 1,000mb to 1,000' at 75.0°F: 0.25" Transposition factor

(transpositioned maximum dew point PW - basin elevation maximum dew point PW)/(storm representative maximum dew point PW - in place storm elevation maximum dew point PW)

= (2.85"- 0.25") / (3.07" - 0.16)

= 2.60 / 2.91

= 0.90 Moisture inflow barrier adjustment factor Transpositioned maximum dew point: 75.0° F Basin effective barrier height: 1,000 Precipitable water for 76.5° F: 3.07" Adjustment for basin ave. elevation, 1,000mb to 1,000' at 76.5°F: 0.25"

180999.51.1008 Revision 1 Attachment 6 Page 5 of 6 Barrier adjustment for basin elevation, 76.5° F, 1,000mb to 1,000': 0.25" Moisture inflow barrier adjustment factor =

(transpositioned maximum dew point PW - effective barrier height elevation maximum dew point PW)/(transpositioned maximum dew point PW - basin elevation maximum PW)

= (3.07"- 0.25) / (3.07" - 0.25)

= 2.82 / 2.82

= 1.00 Total adjustment factor = (In-Place maximization) X (Transposition) X (Barrier Adjustment/Storm elevation)

= 1.084

0.90

1.00

= 0.96 This is the same total adjustment computed earlier (within round-off error) using the single equation to compute the total adjustment factor.

Since these procedures involve linear multiplication, Excel spreadsheets can be used to incorporate the storm DAD and apply the factors to compute the total adjusted DAD. Each storm spreadsheet and all the data used for the calculations are presented for each storm in Attachments 1, 2, and 3.

Once the total adjustment factors are applied to all of the storms being considered, rainfall amounts from largest storms are plotted on a log-linear plot with rainfall depth plotted on the linear scale and area size plotted on the log scale. A separate graph is constructed for each duration period, e.g. 6-hour, 12-hour, etc. The graphs provide curves of the transpositioned maximized adjusted storm rainfall amounts for all area sizes. These DA curves represent the maximum rainfall potential based on standard procedure modifications of the largest observed historic storms in the region surrounding the basins. An enveloping curve is drawn using the largest rainfall values. All of the plotted rainfall amounts either lie on the enveloping curve or below it. The exception is in the case where there is reason to suspect that a value is larger than is reasonable and that rainfall value may be undercut, i.e. the envelop curve should be drawn beneath the value. Undercutting should rarely be done and each case needs to be justified. No undercutting was done in this study. In general, the enveloping curve should provide a smooth transition among the maximum rainfall values for various area sizes. This process of enveloping DA plots provides continuity in space for the rainfall amounts among various area sizes.

After enveloping curves are completed for each of the duration periods, DD curves are plotted on a linear-linear graph, with duration on one axis and depth on the other. Since there is only a single curve for each area size from the enveloped DA plots, all of DA curves can be plotted as a family of curves on a single graph. Enveloping and smoothing of curves is completed for each area size. The curve should provide a smooth

180999.51.1008 Revision 1 Attachment 6 Page 6 of 6 transition among the maximum rainfall values for various durations. This procedure of enveloping DD plots provides continuity in time for the rainfall amounts among various durations.

The final envelopment curves provide the maximum rainfall amounts that represent PMP values for the MNGP basin centroid. Rainfall amounts for each area size and each duration are taken from the curves and used to construct the PMP DAD table.

Enveloped rainfall values were taken from the DA plots and used to construct the DD plots. A curve was constructed for each area size, i.e., 10-; 100-; 200-; 500-; 1,000-;

5,000-; 10,000-; and 20,000-square mile area sizes. Enveloping curves were drawn with smoothing to provide smooth transitions among duration periods.

This procedure of enveloping and smoothing produces maximum rainfall amounts that have continuity in both time and space. Final plots of the DA and DD curves for the basin are provided in this Attachment 7. The final PMP values for the study were taken from the DD curves and used to derive the PMP values.

180999.51.1008 Revision 1 Attachment 7 Page 1 of 13 ATTACHMENT 7: Depth-Area and Depth-Duration Curves Rainfall amounts from the largest storms were plotted on DA plots. Curves were made for each duration period, i.e., 6-, 12-, 24-, 48-, and 72-hour duration periods.

Enveloping curves were drawn using the maximum rainfall values and smoothing was applied to provide smooth transitions among area sizes.

Enveloped rainfall values were taken from the DA plots and used to construct the DD plots. A curve was constructed for each area size, i.e., 10-; 100-; 200-; 500-; 1,000-;

5,000-; 10,000-; 20,000-; 50,000-, and 100,000-square mile area sizes. Enveloping and smoothing was completed to provide smooth transitions among duration periods.

This procedure of enveloping and smoothing produces maximum rainfall amounts that have continuity in both time and space. Final plots of the DA and DD curves for the PINGP basin centroid, for both all season and cool season, are provided in this Attachment. The final PMP values for the study were taken from the DD curves and used to derive the PMP values.

180999.51.1008 Revision 1 Attachment 7 Page 2 of 13 Figure 1: Depth-area chart for the 6-hour duration

180999.51.1008 Revision 1 Attachment 7 Page 3 of 13 Figure 2: Depth-area chart for the 12-hour duration

180999.51.1008 Revision 1 Attachment 7 Page 4 of 13 Figure 3: Depth-area chart for the 24-hour duration

180999.51.1008 Revision 1 Attachment 7 Page 5 of 13 Figure 4: Depth-area chart for the 48-hour duration

180999.51.1008 Revision 1 Attachment 7 Page 6 of 13 Figure 5: Depth-area chart for the 72-hour duration

180999.51.1008 Revision 1 Attachment 7 Page 7 of 13 Figure 6: Depth-duration chart for the all area sizes and durations

180999.51.1008 Revision 1 Attachment 7 Page 8 of 13 Figure 7: Depth-area chart for the cool-season 6-hour duration

180999.51.1008 Revision 1 Attachment 7 Page 9 of 13 Figure 8: Depth-area chart for the cool-season 12-hour duration

180999.51.1008 Revision 1 Attachment 7 Page 10 of 13 Figure 9: Depth-area chart for the cool-season 24-hour duration

180999.51.1008 Revision 1 Attachment 7 Page 11 of 13 Figure 10: Depth-area chart for the cool-season 48-hour duration

180999.51.1008 Revision 1 Attachment 7 Page 12 of 13 Figure 11: Depth-area chart for the cool-season 72-hour duration

180999.51.1008 Revision 1 Attachment 7 Page 13 of 13 Figure 12: Depth-duration chart cool-season

ML15162A310

Text

Reference:

1.0 Purpose and Scope

1.0 Purpose and Scope

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