STOKE-051 Final Report

DAM HYDRAULIC CAPACITY
ASSESSMENT REPORT
(DRAFT)
TOWN FORK CREEK WS DAM #13
STOKE-051
STOKES COUNTY, NC
PREPARED BY:
HDR Engineering Inc. of the
Carolinas under contract with
WOOD E&I Solutions
2020

EXECUTIVE SUMMARY
A hydraulic capacity analysis was completed for the Town Fork Creek WS Dam #13 in Stokes
County, North Carolina. The purpose of the study was to analyze the existing potential of the dam
for overtopping during predetermined specified rainfall events using the North Carolina Dam
Safety defined process and templates. The analyses were completed using the United States
Army Corps of Engineers developed software Hydrologic Engineering Center – Hydrologic
Modeling System (HEC-HMS) in combination with Arc-GIS to develop required input parameters.
The rainfall events included in the analyses consist of 24-hour durations with return periods of
25 years, 50 years, 100 years, 200 years, 500 years and 1000 years. Results of the analyses
indicate that this structure is hydraulically adequate for 25 years, 50 years, 100 years, 200 years,
500 years, and 1000 years rainfall events. Data, input parameters, and final results can be found
on the attached summary sheets and in the appendices of this report as well as in the associated
electronic file in which all program files are stored.
Drainage Area (Sq. Mi.)=
Curve Number =
Lag Time (min.)=
Rainfall Distribution Methods =
547.2
455.8
470.5
485.4
500.6
515.9
531.5
727.4
727.9
728.4
728.9
729.4
ELEVATION
724.9
725.4
725.9
726.4
726.9
43.9
51.1
58.6
STORAGE (ACRE-FT)
0.0
5.6
11.3
17.9
23.9
30.3
36.9
708.9
705.9
706.4
706.9
707.4
707.9
708.4
716.4
721.6
ELEVATION
704.4
704.9
705.4
STORAGE (ACRE-FT)
412.6
426.8
441.2
66.88
56
SCS Type 2
SPILLWAY
Primary
Auxiliary
TYPE
Riser / Barrel
Grass Lined Trapezoidal Channel
ELEVATION
24 HOUR - 200 YEAR EVENT, 9.36 INCHES, ELEVATION 722.7 (2.1 FT FREE-BOARD)
24 HOUR - 100 YEAR EVENT, 8.29 INCHES, ELEVATION 721.8 (3 FT FREE-BOARD)
24 HOUR - 50 YEAR EVENT, 7.3 INCHES, ELEVATION 719.6 (5.2 FT FREE-BOARD)
24 HOUR - 25 YEAR EVENT, 6.37 INCHES, ELEVATION 717.5 (7.3 FT FREE-BOARD)
SUMMARY OF INPUT PARAMETERS
2
SUMMARY SHEET OF HYDRAULIC CAPACITY RESULTS
TOWN FORK CREEK WS DAM #13, STOKE-051
ANALYSIS PERFORMED BY: S. MURPHY, HDR
TOP OF DAM ELEVATION = 724.8
24 HOUR - 1000 YEAR EVENT, 12.2 INCHES, ELEVATION 724.5 (0.3 FT FREE-BOARD)
24 HOUR - 500 YEAR EVENT, 10.9 INCHES, ELEVATION 723.7 (1.1 FT FREE-BOARD)
STOKE-051TOWN FORK CREEK WS DAM #13 OCTOBER 27, 2020
1309.5
NOT TO SCALE
1125.6
1155.2
1185.2
1215.6
1246.4
1277.6
956.1
983.4
1011.0
1039.1
1067.5
1096.4
800.6
825.5
850.8
876.5
902.7
929.2
662.3
684.0
706.1
728.9
752.2
776.2
563.2
580.8
600.4
620.5
641.1
742.4
742.9
743.4
743.9
744.4
739.4
739.9
740.4
740.9
741.4
741.9
736.4
736.9
737.4
737.9
738.4
738.9
733.4
733.9
734.4
734.9
735.4
735.9
730.4
730.9
731.4
731.9
732.4
732.9
729.9
357.8
371.3
384.9
398.7
281.4
293.7
306.1
318.7
331.6
344.6
211.7
222.9
234.2
245.8
257.5
269.3
148.3
158.5
168.8
179.3
190.0
200.8
91.6
100.5
109.7
119.0
128.6
138.4
66.4
74.6
83.0
723.9
724.4
720.9
721.4
721.9
722.4
722.9
723.4
717.9
718.4
718.9
719.4
719.9
720.4
714.9
715.4
715.9
716.4
716.9
717.4
711.9
712.4
712.9
713.4
713.9
714.4
709.4
709.9
710.4
710.9
711.4
STOKE-051TOWN FORK CREEK WS DAM #13 OCTOBER 27, 2020

APPENDIX A
Watershed Boundary

Sources: Esri, HERE, Garmin, USGS, Intermap, INCREMENT P,NRCan, Esri Japan, METI, Esri China (Hong Kong), Esri Korea,Esri (Thailand), NGCC, (c) OpenStreetMap contributors, and theGIS User Community
Town Fork Creek WS Dam #13 - STOKE-051 - Watershed Boundary
Legend
Longest FlowPath
Watershed Bound ary
0 0.55 1.10.275 Miles
Date: 10 /2/2020
/Drainage Ar ea: 2.0 Square MilesFlowpath Length: 2.8 miles

APPENDIX B

Lag Time Calculation
Dam No:STOKE-051 Date:10/26/2020
Dam Name:Town Fork Creek WS Dam #13 Engineer:K. Trefzger
Maximum Potential Retention (inches):S =(1000/cn')-10
Time of Concentration (hours):Tc =l0.8*(S+1)0.7
1140*Y0.5
Basin Data:Input Values in yellow
Curve Number CN =66.8762 from NRCS CN Calculation
S =4.95301 in.
Mean Basin Slope Y =18.1123 %from Watershed Mean slope
Longest Flowpath:2.82 mi.from Watershed Longest flowpath
Flow Length l =14889.6 ft.
Time of Concentration Tc =1.57 Hours Tc =94 mins
Lag Time TL =0.94 Hours TL =56 mins

APPENDIX C
NRCS Curve Number Summary Sheet

Change CN according to TR-55 (see tables below)
NLCD (2016) Landuse TR-55 Landuse HSG A (sq. ft.)CN HSG B (sq. ft.)CN HSG C (sq. ft.)CN HSG D (sq. ft.)CN
Open Water Not Available 0 100 0 81443 100 8144347 51747 100 5174700 647387 100 64738725
Developed, Open Space Open space - Fair condition (grass cover 50% to 75%)0 49 0 833995 69 57545631 1546694 79 122188842 0 84 0
Developed, Low Intensity Residential districts by average lot size: 1/3 acre 0 57 0 36488 72 2627124 112437 81 9107403 0 86 0
Developed, Medium Intensity Residential districts by average lot size: 1/8 acre 0 77 0 0 85 0 0 90 0 0 92 0
Developed, High Intensity Urban districts - Commercial and business 0 89 0 0 92 0 0 94 0 0 95 0
Barren Land Newly graded areas 0 77 0 0 86 0 0 91 0 0 94 0
Deciduous Forest Woods - Fair 0 36 0 21132991 60 1267979463 8947055 73 653135029 207825 79 16418181
Evergreen Forest Woods - Fair 0 36 0 4095650 60 245738972 3905994 73 285137565 34070 79 2691569
Mixed Forest Woods - Fair 0 36 0 4461015 60 267660892 2316131 73 169077551 25496 79 2014158
Shrub/Scrub Brush - Fair 0 35 0 173474 56 9714566 273252 70 19127661 612 77 47095
Herbaceuous Herbaceuous - Fair 0 60 0 691379 71 49087874 899657 81 72872230 45532 89 4052330
Hay/Pasture Pasture - Fair 0 49 0 1949524 69 134517160 3198511 79 252682368 3178 84 266963
Cultivated Crops Row crops (SR + CR) - Poor 0 71 0 0 80 0 9663 87 840662 0 90 0
Woody Wetlands Not Available 0 80 0 0 85 0 41218 90 3709653 7223 95 686181
Emergent Herbaceuous Wetlands Not Available 0 80 0 0 85 0 0 90 0 0 95 0 Weighted CN=66.88
NOTE: Curve Numbers are from SCS TR-55 with the exception of assumed HSG A (CN=60) for Herbaceous,Open Water, Woody Wetlands, and Emergent Herbaceous
Wetlands.
NOTE: double-check all the land types are being calculated and texts are accurate
NOTE: double-check the exported attribute table has the same table format as the "Export_Output" table

APPENDIX D
Hyetograph Results Used for Analysis

0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24Cumulative Depth (in)Time (hrs)
Hyetographs for 24-Hour SCS Type II Rainfall Distributions
25YR
50YR
100YR
200YR
500YR
1000YR

APPENDIX E
NOAA Atlas 14 Rainfall Table

Point precipitation frequency estimates (inches)
NOAA Atlas 14 Volume 2 Version 3
Data type: Precipitation depth
Time series type: Partial duration
Project area: Ohio River Basin
Location name (ESRI Maps): Walnut Cove, North Carolina USA
Station Name: -
Latitude: 36.30938°
Longitude: -80.223418°
Elevation (USGS): 778.65 ft
PRECIPITATION FREQUENCY ESTIMATES
by
duration
for ARI
(years):1 2 5 10 25 50 100 200 500 1000
5-min:0.369 0.44 0.519 0.574 0.639 0.684 0.725 0.763 0.807 0.838
10-min:0.59 0.703 0.831 0.918 1.02 1.09 1.15 1.21 1.28 1.32
15-min:0.737 0.884 1.05 1.16 1.29 1.38 1.46 1.53 1.61 1.66
30-min:1.01 1.22 1.49 1.68 1.91 2.08 2.23 2.38 2.56 2.68
60-min:1.26 1.53 1.91 2.19 2.55 2.81 3.07 3.33 3.67 3.92
2-hr:1.51 1.84 2.32 2.67 3.15 3.53 3.9 4.28 4.8 5.2
3-hr:1.63 1.99 2.51 2.9 3.43 3.84 4.25 4.68 5.25 5.7
6-hr:2.02 2.46 3.09 3.59 4.27 4.81 5.38 5.97 6.8 7.46
12-hr:2.47 3 3.78 4.4 5.29 6.01 6.78 7.59 8.76 9.72
24-hr:2.93 3.55 4.49 5.26 6.37 7.3 8.29 9.36 10.9 12.2
2-day:3.45 4.17 5.24 6.1 7.31 8.3 9.35 10.5 12 13.3
3-day:3.65 4.41 5.54 6.44 7.71 8.75 9.85 11 12.7 14.1
4-day:3.86 4.65 5.83 6.77 8.11 9.2 10.3 11.6 13.3 14.8
7-day:4.39 5.27 6.5 7.5 8.89 10 11.2 12.5 14.2 15.7
10-day:5 5.97 7.28 8.33 9.78 11 12.2 13.4 15.2 16.6
20-day:6.75 8.01 9.59 10.8 12.5 13.9 15.2 16.6 18.5 19.9
30-day:8.35 9.86 11.6 12.9 14.5 15.8 17.1 18.3 20 21.2
45-day:10.5 12.4 14.3 15.8 17.7 19.1 20.5 21.9 23.6 24.9
60-day:12.6 14.7 16.8 18.4 20.4 21.9 23.3 24.7 26.4 27.7
Date/time (GMT): Mon Oct 26 18:41:51 2020
pyRunTime: 0.0415620803833

APPENDIX F
Outlet Works Rating Curves

Total outlet discharge from the spillway system
Client:NCEM Date:10/26/2020
Project:Overtopping Study Engineer:T.Carter
Dam:Town Fork Creek WS Dam #13 Dam No.STOKE-051
Reservior Water
Level (RWS)
Elevation (ft)
Total discharge from the
spillway system (cfs)
(from Hydrocad)
704.4 0.0
705.2 4.3
706.0 12.0
706.8 17.2
707.6 21.1
708.4 24.4
709.2 27.2
710.0 29.8
710.8 32.2
711.6 34.4
712.4 36.5
713.2 38.4
714.0 40.3
714.8 42.1
715.6 43.8
716.4 45.4
717.2 81.5
718.0 112.4
718.8 114.0
719.6 115.5
720.4 117.0
721.2 118.4
722.0 205.2
722.8 575.5
723.6 1123.2
724.4 1819.7
725.2 2653.4
726.0 3618.1
726.8 4669.3
727.6 5458.1
728.4 6115.7
729.2 6698.7
730.0 7229.8
730.8 7721.6
731.6 8182.1
732.4 8616.7
733.2 9029.6
734.0 9423.8
734.8 9801.7
735.6 10165.2
736.4 10515.8
737.2 10854.8
738.0 11183.4
738.8 11502.4
739.6 11812.7
740.4 12114.9
741.2 12409.7
0.0
2000.0
4000.0
6000.0
8000.0
10000.0
12000.0
14000.0
700.0 705.0 710.0 715.0 720.0 725.0 730.0 735.0 740.0 745.0Total discharge from the spillway system (cfs)Reservior Water Level (RWS) Elevation (ft)
The whole spillway system rating curve (cfs)
STOKE-051 Town Fork Creek WS Dam #13
Rainfall not specifiedSTOKE-051
Printed 10/26/2020Prepared by HDR, Inc
Page 1HydroCAD® 10.00-25 s/n 07102 © 2019 HydroCAD Software Solutions LLC
Summary for Pond 1P: STOKE-051 Town Fork Creek WS Dam #13
Volume Invert Avail.Storage Storage Description
#1 704.40' 57,025,452 cf Custom Stage Data (Prismatic) Listed below (Recalc)
STOKE-051 Town Fork Creek WS Dam #13
Rainfall not specifiedSTOKE-051
Printed 10/26/2020Prepared by HDR, Inc
Page 2HydroCAD® 10.00-25 s/n 07102 © 2019 HydroCAD Software Solutions LLC
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
704.40 501,084 0 0
704.90 501,084 250,542 250,542
705.40 501,084 250,542 501,084
705.90 517,236 254,580 755,664
706.40 540,205 264,360 1,020,024
706.90 566,113 276,580 1,296,604
707.40 591,543 289,414 1,586,018
707.90 615,771 301,829 1,887,846
708.40 641,572 314,336 2,202,182
708.90 668,037 327,402 2,529,584
709.40 695,693 340,933 2,870,517
709.90 721,113 354,202 3,224,718
710.40 743,135 366,062 3,590,780
710.90 764,365 376,875 3,967,655
711.40 786,406 387,693 4,355,348
711.90 806,709 398,279 4,753,627
712.40 825,430 408,035 5,161,662
712.90 843,447 417,219 5,578,881
713.40 859,795 425,811 6,004,691
713.90 875,146 433,735 6,438,427
714.40 891,543 441,672 6,880,099
714.90 906,973 449,629 7,329,728
715.40 921,689 457,166 7,786,893
715.90 935,195 464,221 8,251,114
716.40 949,131 471,082 8,722,196
716.90 963,828 478,240 9,200,436
717.40 979,746 485,894 9,686,329
717.90 995,771 493,879 10,180,208
718.40 1,011,670 501,860 10,682,069
718.90 1,027,422 509,773 11,191,842
719.40 1,042,949 517,593 11,709,434
719.90 1,059,004 525,488 12,234,923
720.40 1,075,508 533,628 12,768,551
720.90 1,091,045 541,638 13,310,189
721.40 1,108,691 549,934 13,860,123
721.90 1,126,865 558,889 14,419,012
722.40 1,145,107 567,993 14,987,005
722.90 1,161,533 576,660 15,563,665
723.40 1,177,617 584,788 16,148,452
723.90 1,193,770 592,847 16,741,299
724.40 1,210,400 601,043 17,342,342
724.90 1,226,738 609,285 17,951,626
725.40 1,243,447 617,546 18,569,172
725.90 1,260,303 625,938 19,195,110
726.40 1,276,445 634,187 19,829,297
726.90 1,292,949 642,349 20,471,645
727.40 1,310,000 650,737 21,122,383
727.90 1,327,568 659,392 21,781,775
728.40 1,346,035 668,401 22,450,175
STOKE-051 Town Fork Creek WS Dam #13
Rainfall not specifiedSTOKE-051
Printed 10/26/2020Prepared by HDR, Inc
Page 3HydroCAD® 10.00-25 s/n 07102 © 2019 HydroCAD Software Solutions LLC
728.90 1,364,102 677,534 23,127,710
729.40 1,382,832 686,734 23,814,443
729.90 1,401,768 696,150 24,510,593
730.40 1,694,365 774,033 25,284,626
730.90 1,725,811 855,044 26,139,670
731.40 1,774,063 874,969 27,014,639
731.90 1,820,684 898,687 27,913,326
732.40 1,864,717 921,350 28,834,676
732.90 1,911,406 944,031 29,778,707
733.40 1,956,885 967,073 30,745,779
733.90 2,007,285 991,043 31,736,822
734.40 2,058,799 1,016,521 32,753,343
734.90 2,106,182 1,041,245 33,794,588
735.40 2,148,145 1,063,582 34,858,170
735.90 2,186,846 1,083,748 35,941,918
736.40 2,224,297 1,102,786 37,044,703
736.90 2,260,488 1,121,196 38,165,900
737.40 2,294,209 1,138,674 39,304,574
737.90 2,326,787 1,155,249 40,459,823
738.40 2,359,775 1,171,641 41,631,463
738.90 2,392,871 1,188,162 42,819,625
739.40 2,426,631 1,204,876 44,024,500
739.90 2,461,572 1,222,051 45,246,551
740.40 2,495,068 1,239,160 46,485,711
740.90 2,529,033 1,256,025 47,741,736
741.40 2,562,285 1,272,830 49,014,566
741.90 2,596,016 1,289,575 50,304,141
742.40 2,630,195 1,306,553 51,610,694
742.90 2,664,326 1,323,630 52,934,324
743.40 2,702,529 1,341,714 54,276,038
743.90 2,747,256 1,362,446 55,638,484
744.40 2,800,615 1,386,968 57,025,452
Device Routing Invert Outlet Devices
#1 Primary 688.60'30.0" Round 30" RCP
L= 224.0' RCP, square edge headwall, Ke= 0.500
Inlet / Outlet Invert= 688.60' / 686.40' S= 0.0098 '/' Cc= 0.900
n= 0.013, Flow Area= 4.91 sf
#2 Device 1 704.40'22.5" W x 18.0" H Vert. Riser Orifice C= 0.600
#3 Device 1 716.40'90.0" W x 15.0" H Vert. Riser Weir X 2.00 C= 0.600
#4 Secondary 721.60'Emergency Spillway, Cv= 3.10 (C= 3.88)
Head (feet) 0.00 1.00 2.00 3.00 4.00 5.00
Width (feet) 86.00 92.60 99.20 105.80 112.40 119.00
Primary OutFlow Max=0.00 cfs @ 5.00 hrs HW=0.00' TW=683.10' (Fixed TW Elev= 683.10')
1=30" RCP ( Controls 0.00 cfs)
2=Riser Orifice ( Controls 0.00 cfs)
3=Riser Weir ( Controls 0.00 cfs)
Secondary OutFlow Max=0.00 cfs @ 5.00 hrs HW=0.00' (Free Discharge)
4=Emergency Spillway ( Controls 0.00 cfs)
STOKE-051 Town Fork Creek WS Dam #13
Rainfall not specifiedSTOKE-051
Printed 10/26/2020Prepared by HDR, Inc
Page 4HydroCAD® 10.00-25 s/n 07102 © 2019 HydroCAD Software Solutions LLC
Stage-Discharge for Pond 1P: STOKE-051 Town Fork Creek WS Dam #13
Elevation
(feet)
Discharge
(cfs)
Primary
(cfs)
Secondary
(cfs)
704.40 0.00 0.00 0.00
704.80 1.52 1.52 0.00
705.20 4.31 4.31 0.00
705.60 7.91 7.91 0.00
706.00 11.99 11.99 0.00
706.40 14.90 14.90 0.00
706.80 17.24 17.24 0.00
707.20 19.28 19.28 0.00
707.60 21.11 21.11 0.00
708.00 22.79 22.79 0.00
708.40 24.36 24.36 0.00
708.80 25.83 25.83 0.00
709.20 27.21 27.21 0.00
709.60 28.53 28.53 0.00
710.00 29.79 29.79 0.00
710.40 31.00 31.00 0.00
710.80 32.17 32.17 0.00
711.20 33.29 33.29 0.00
711.60 34.37 34.37 0.00
712.00 35.43 35.43 0.00
712.40 36.45 36.45 0.00
712.80 37.44 37.44 0.00
713.20 38.41 38.41 0.00
713.60 39.35 39.35 0.00
714.00 40.27 40.27 0.00
714.40 41.18 41.18 0.00
714.80 42.06 42.06 0.00
715.20 42.92 42.92 0.00
715.60 43.77 43.77 0.00
716.00 44.60 44.60 0.00
716.40 45.41 45.41 0.00
716.80 58.40 58.40 0.00
717.20 81.45 81.45 0.00
717.60 111.07 111.07 0.00
718.00 112.41 112.41 0.00
718.40 113.18 113.18 0.00
718.80 113.95 113.95 0.00
719.20 114.71 114.71 0.00
719.60 115.46 115.46 0.00
720.00 116.21 116.21 0.00
720.40 116.96 116.96 0.00
720.80 117.70 117.70 0.00
721.20 118.43 118.43 0.00
721.60 119.16 119.16 0.00
722.00 205.23 119.89 85.34
722.40 364.92 120.61 244.31
722.80 575.54 121.33 454.21
723.20 829.62 122.04 707.58
723.60 1,123.20 122.75 1,000.44
724.00 1,453.79 123.46 1,330.33
724.40 1,819.74 124.16 1,695.58
Elevation
(feet)
Discharge
(cfs)
Primary
(cfs)
Secondary
(cfs)
724.80 2,219.88 124.86 2,095.03
725.20 2,653.38 125.55 2,527.83
725.60 3,119.60 126.24 2,993.36
726.00 3,618.10 126.93 3,491.18
726.40 4,148.55 127.61 4,020.94
726.80 4,669.27 128.29 4,540.98
727.20 5,087.22 128.96 4,958.25
727.60 5,458.13 129.64 5,328.50
728.00 5,798.38 130.30 5,668.07
728.40 6,115.70 130.97 5,984.73
728.80 6,414.75 131.63 6,283.12
729.20 6,698.70 132.29 6,566.41
729.60 6,969.81 132.94 6,836.87
730.00 7,229.81 133.60 7,096.22
730.40 7,480.04 134.24 7,345.80
730.80 7,721.60 134.89 7,586.71
731.20 7,955.36 135.53 7,819.82
731.60 8,182.06 136.17 8,045.89
732.00 8,402.34 136.81 8,265.54
732.40 8,616.73 137.44 8,479.29
732.80 8,825.70 138.07 8,687.63
733.20 9,029.64 138.70 8,890.94
733.60 9,228.91 139.32 9,089.59
734.00 9,423.83 139.95 9,283.89
734.40 9,614.68 140.56 9,474.12
734.80 9,801.71 141.18 9,660.52
735.20 9,985.13 141.79 9,843.34
735.60 10,165.17 142.41 10,022.76
736.00 10,341.99 143.01 10,198.98
736.40 10,515.77 143.62 10,372.15
736.80 10,686.67 144.22 10,542.45
737.20 10,854.82 144.83 10,710.00
737.60 11,020.36 145.42 10,874.94
738.00 11,183.40 146.02 11,037.38
738.40 11,344.06 146.61 11,197.45
738.80 11,502.44 147.20 11,355.23
739.20 11,658.63 147.79 11,510.83
739.60 11,812.72 148.38 11,664.34
740.00 11,964.80 148.96 11,815.84
740.40 12,114.94 149.55 11,965.40
740.80 12,263.22 150.13 12,113.10
741.20 12,409.71 150.70 12,259.01
741.60 12,554.46 151.28 12,403.19
742.00 12,697.55 151.85 12,545.70
742.40 12,839.02 152.42 12,686.60
742.80 12,978.93 152.99 12,825.94
743.20 13,117.33 153.56 12,963.78
743.60 13,254.28 154.12 13,100.15
744.00 13,389.80 154.68 13,235.12
744.40 13,523.96 155.24 13,368.71