STOKE-052 Final Report

DAM HYDRAULIC CAPACITY
ASSESSMENT REPORT
(DRAFT)
TOWN FORK CREEK WS DAM #14A
STOKE-052
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 #14A 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 =
569.8
457.3
474.9
492.9
511.5
530.5
549.9
759.2
759.7
760.2
760.7
761.2
ELEVATION
756.7
757.2
757.7
758.2
758.7
35.7
41.8
48.2
STORAGE (ACRE-FT)
0.0
4.4
9.0
13.8
18.8
24.1
29.8
740.7
737.7
738.2
738.7
739.2
739.7
740.2
748.2
757.4
ELEVATION
736.2
736.7
737.2
STORAGE (ACRE-FT)
407.2
423.5
440.2
66.98
72
SCS Type 2
SPILLWAY
Primary
Auxiliary
TYPE
Riser / Barrel
Grass Lined Trapezoidal Channel
ELEVATION
24 HOUR - 200 YEAR EVENT, 9.46 INCHES, ELEVATION 758.5 (4.7 FT FREE-BOARD)
24 HOUR - 100 YEAR EVENT, 8.36 INCHES, ELEVATION 757.9 (5.3 FT FREE-BOARD)
24 HOUR - 50 YEAR EVENT, 7.35 INCHES, ELEVATION 756.4 (6.8 FT FREE-BOARD)
24 HOUR - 25 YEAR EVENT, 6.41 INCHES, ELEVATION 753.1 (10.1 FT FREE-BOARD)
SUMMARY OF INPUT PARAMETERS
2.69
SUMMARY SHEET OF HYDRAULIC CAPACITY RESULTS
TOWN FORK CREEK WS DAM #14A, STOKE-052
ANALYSIS PERFORMED BY: S. MURPHY, HDR
TOP OF DAM ELEVATION = 763.2
24 HOUR - 1000 YEAR EVENT, 12.4 INCHES, ELEVATION 760 (3.2 FT FREE-BOARD)
24 HOUR - 500 YEAR EVENT, 11.1 INCHES, ELEVATION 759.4 (3.8 FT FREE-BOARD)
STOKE-052TOWN FORK CREEK WS DAM #14A OCTOBER 27, 2020
1351.2
NOT TO SCALE
1165.5
1195.4
1225.8
1256.5
1287.7
1319.3
994.9
1022.3
1050.0
1078.2
1106.9
1136.0
839.0
864.0
889.5
915.2
941.4
968.0
697.2
719.8
742.8
766.3
790.1
814.4
590.1
610.7
631.8
653.2
675.0
774.2
774.7
775.2
775.7
776.2
771.2
771.7
772.2
772.7
773.2
773.7
768.2
768.7
769.2
769.7
770.2
770.7
765.2
765.7
766.2
766.7
767.2
767.7
762.2
762.7
763.2
763.7
764.2
764.7
761.7
345.8
360.7
375.8
391.3
263.3
276.3
289.6
303.2
317.1
331.3
190.6
202.0
213.8
225.8
238.0
250.5
128.0
137.7
147.7
157.9
168.5
179.4
76.5
84.3
92.4
100.8
109.6
118.7
54.9
61.9
69.1
755.7
756.2
752.7
753.2
753.7
754.2
754.7
755.2
749.7
750.2
750.7
751.2
751.7
752.2
746.7
747.2
747.7
748.2
748.7
749.2
743.7
744.2
744.7
745.2
745.7
746.2
741.2
741.7
742.2
742.7
743.2
STOKE-052TOWN FORK CREEK WS DAM #14A 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 #14A - STOKE-052 - Watershed Boundary
Legend
Longest FlowPath
Watershed Bound ary
0 0.8 1.60.4 Miles
Date: 10 /2/2020
/Drainage Area: 2.69 Square MilesFlowpath Length: 3.5 miles

APPENDIX B

Lag Time Calculation
Dam No:STOKE-052 Date:10/26/2020
Dam Name:Town Fork Creek WS Dam #14A 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 =66.9806 from NRCS CN Calculation
S =4.92969 in.
Mean Basin Slope Y =15.4548 %from Watershed Mean slope
Longest Flowpath:3.47 mi.from Watershed Longest flowpath
Flow Length l =18321.6 ft.
Time of Concentration Tc =2.00 Hours Tc =120 mins
Lag Time TL =1.20 Hours TL =72 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 46579 100 4657887 1892 100 189184 193738 100 19373778
Developed, Open Space Open space - Fair condition (grass cover 50% to 75%)0 49 0 2119306 69 146232091 1013167 79 80040220 9581 84 804830
Developed, Low Intensity Residential districts by average lot size: 1/3 acre 0 57 0 285816 72 20578763 90361 81 7319251 24170 86 2078604
Developed, Medium Intensity Residential districts by average lot size: 1/8 acre 0 77 0 4341 85 368970 3410 90 306863 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 11431 86 983063 0 91 0 95141 94 8943222
Deciduous Forest Woods - Fair 0 36 0 27369915 60 1642194891 13411758 73 979058345 152127 79 12018021
Evergreen Forest Woods - Fair 0 36 0 3271382 60 196282940 3293210 73 240404348 8289 79 654823
Mixed Forest Woods - Fair 0 36 0 2830585 60 169835076 1686216 73 123093736 18922 79 1494870
Shrub/Scrub Brush - Fair 0 35 0 2322852 56 130079734 1697839 70 118848729 0 77 0
Herbaceuous Herbaceuous - Fair 0 60 0 2011736 71 142833260 2028009 81 164268737 957 89 85194
Hay/Pasture Pasture - Fair 0 49 0 6025476 69 415757837 4964604 79 392203710 79194 84 6652295
Cultivated Crops Row crops (SR + CR) - Poor 0 71 0 43586 80 3486912 7973 87 693653 0 90 0
Woody Wetlands Not Available 0 80 0 0 85 0 0 90 0 0 95 0
Emergent Herbaceuous Wetlands Not Available 0 80 0 0 85 0 0 90 0 0 95 0 Weighted CN=66.98
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: 36.325592°
Longitude: -80.207058°
Elevation (USGS): 950.53 ft
PRECIPITATION FREQUENCY ESTIMATES
by
duration
for ARI
(years):1 2 5 10 25 50 100 200 500 1000
5-min:0.369 0.439 0.518 0.574 0.639 0.683 0.725 0.762 0.805 0.836
10-min:0.589 0.703 0.83 0.917 1.02 1.09 1.15 1.21 1.27 1.32
15-min:0.737 0.883 1.05 1.16 1.29 1.38 1.46 1.52 1.6 1.65
30-min:1.01 1.22 1.49 1.68 1.91 2.08 2.23 2.37 2.55 2.68
60-min:1.26 1.53 1.91 2.19 2.55 2.81 3.07 3.33 3.66 3.91
2-hr:1.51 1.84 2.32 2.67 3.15 3.53 3.91 4.29 4.8 5.2
3-hr:1.64 2 2.51 2.91 3.43 3.84 4.26 4.68 5.25 5.7
6-hr:2.03 2.46 3.09 3.59 4.27 4.82 5.39 5.98 6.81 7.47
12-hr:2.47 3 3.79 4.42 5.3 6.03 6.8 7.62 8.8 9.76
24-hr:2.93 3.55 4.5 5.28 6.41 7.35 8.36 9.46 11.1 12.4
2-day:3.46 4.18 5.26 6.13 7.36 8.36 9.43 10.6 12.2 13.5
3-day:3.66 4.42 5.55 6.47 7.76 8.82 9.94 11.1 12.9 14.3
4-day:3.86 4.66 5.85 6.81 8.16 9.27 10.5 11.7 13.5 15
7-day:4.4 5.28 6.52 7.53 8.94 10.1 11.3 12.6 14.4 15.9
10-day:5 5.98 7.3 8.36 9.84 11 12.3 13.5 15.3 16.8
20-day:6.76 8.03 9.62 10.9 12.6 13.9 15.3 16.7 18.6 20
30-day:8.36 9.88 11.6 12.9 14.6 15.9 17.2 18.4 20.1 21.3
45-day:10.5 12.4 14.4 15.9 17.8 19.2 20.6 22 23.7 25
60-day:12.6 14.7 16.9 18.5 20.5 22 23.4 24.8 26.6 27.8
Date/time (GMT): Mon Oct 26 18:50:59 2020
pyRunTime: 0.0511298179626

APPENDIX F
Outlet Works Rating Curves

Total outlet discharge from the spillway system
Client:NCEM Date:10/23/2020
Project:Overtopping Study Engineer:T.Carter
Dam:Town Fork Creek WS Dam #14A Dam No.STOKE-052
Reservior Water
Level (RWS)
Elevation (ft)
Total discharge from the
spillway system (cfs)
(from Hydrocad)
736.2 0.0
737.0 4.3
737.8 12.0
738.6 17.2
739.4 21.1
740.2 24.4
741.0 27.2
741.8 29.8
742.6 32.2
743.4 34.4
744.2 36.5
745.0 38.4
745.8 40.3
746.6 42.1
747.4 43.8
748.2 45.4
749.0 81.5
749.8 105.9
750.6 107.1
751.4 108.4
752.2 109.6
753.0 110.7
753.8 111.9
754.6 113.1
755.4 114.2
756.2 115.4
757.0 116.5
757.8 265.7
758.6 899.9
759.4 1825.2
760.2 2986.5
761.0 4359.0
761.8 5928.3
762.6 7685.5
763.4 9624.5
764.2 11741.3
765.0 14033.1
765.8 16294.8
766.6 18068.0
767.4 19622.9
768.2 21037.8
769.0 22349.6
769.8 23580.0
770.6 24743.8
771.4 25851.3
772.2 26910.4
773.0 27927.4
0.0
5000.0
10000.0
15000.0
20000.0
25000.0
30000.0
730.0 735.0 740.0 745.0 750.0 755.0 760.0 765.0 770.0 775.0Total discharge from the spillway system (cfs)Reservior Water Level (RWS) Elevation (ft)
The whole spillway system rating curve (cfs)
STOKE-052 Town Fork Creek WS Dam #14A
Rainfall not specifiedSTOKE-052
Printed 10/23/2020Prepared by HDR, Inc
Page 1HydroCAD® 10.00-25 s/n 07102 © 2019 HydroCAD Software Solutions LLC
Summary for Pond 1P: STOKE-052 Town Fork Creek WS Dam #14A
Volume Invert Avail.Storage Storage Description
#1 736.20' 58,857,739 cf Custom Stage Data (Prismatic) Listed below (Recalc)
STOKE-052 Town Fork Creek WS Dam #14A
Rainfall not specifiedSTOKE-052
Printed 10/23/2020Prepared 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)
736.20 386,133 0 0
736.70 390,020 194,038 194,038
737.20 406,787 199,202 393,240
737.70 424,951 207,935 601,175
738.20 448,174 218,281 819,456
738.70 479,365 231,885 1,051,341
739.20 502,686 245,513 1,296,853
739.70 524,717 256,851 1,553,704
740.20 547,861 268,145 1,821,849
740.70 570,527 279,597 2,101,446
741.20 593,350 290,969 2,392,415
741.70 614,756 302,027 2,694,441
742.20 639,033 313,447 3,007,889
742.70 664,863 325,974 3,333,863
743.20 692,578 339,360 3,673,223
743.70 718,701 352,820 4,026,043
744.20 747,041 366,436 4,392,478
744.70 776,973 381,004 4,773,482
745.20 804,395 395,342 5,168,824
745.70 830,938 408,833 5,577,657
746.20 855,293 421,558 5,999,215
746.70 878,984 433,569 6,432,784
747.20 905,137 446,030 6,878,814
747.70 934,951 460,022 7,338,836
748.20 962,559 474,378 7,813,214
748.70 987,197 487,439 8,300,653
749.20 1,011,504 499,675 8,800,328
749.70 1,034,355 511,465 9,311,793
750.20 1,057,031 522,847 9,834,639
750.70 1,078,750 533,945 10,368,584
751.20 1,101,416 545,042 10,913,626
751.70 1,123,086 556,126 11,469,751
752.20 1,145,430 567,129 12,036,880
752.70 1,171,807 579,309 12,616,190
753.20 1,197,246 592,263 13,208,453
753.70 1,223,477 605,181 13,813,634
754.20 1,250,801 618,570 14,432,203
754.70 1,277,568 632,092 15,064,295
755.20 1,305,898 645,867 15,710,162
755.70 1,335,801 660,425 16,370,587
756.20 1,367,598 675,850 17,046,436
756.70 1,400,781 692,095 17,738,531
757.20 1,433,896 708,669 18,447,200
757.70 1,471,182 726,270 19,173,470
758.20 1,513,584 746,192 19,919,661
758.70 1,551,006 766,148 20,685,809
759.20 1,593,916 786,231 21,472,039
759.70 1,634,629 807,136 22,279,176
760.20 1,674,502 827,283 23,106,458
STOKE-052 Town Fork Creek WS Dam #14A
Rainfall not specifiedSTOKE-052
Printed 10/23/2020Prepared by HDR, Inc
Page 3HydroCAD® 10.00-25 s/n 07102 © 2019 HydroCAD Software Solutions LLC
760.70 1,714,287 847,197 23,953,656
761.20 1,748,037 865,581 24,819,237
761.70 1,781,992 882,507 25,701,744
762.20 1,816,748 899,685 26,601,429
762.70 1,849,580 916,582 27,518,011
763.20 1,882,998 933,145 28,451,155
763.70 1,918,057 950,264 29,401,419
764.20 1,952,275 967,583 30,369,002
764.70 1,987,031 984,827 31,353,829
765.20 2,023,584 1,002,654 32,356,482
765.70 2,060,762 1,021,087 33,377,569
766.20 2,095,459 1,039,055 34,416,624
766.70 2,129,424 1,056,221 35,472,845
767.20 2,163,525 1,073,237 36,546,082
767.70 2,197,090 1,090,154 37,636,236
768.20 2,229,990 1,106,770 38,743,006
768.70 2,263,379 1,123,342 39,866,348
769.20 2,296,416 1,139,949 41,006,297
769.70 2,330,371 1,156,697 42,162,994
770.20 2,365,273 1,173,911 43,336,905
770.70 2,399,668 1,191,235 44,528,140
771.20 2,437,178 1,209,212 45,737,351
771.70 2,476,240 1,228,355 46,965,706
772.20 2,514,834 1,247,769 48,213,474
772.70 2,553,564 1,267,100 49,480,574
773.20 2,590,117 1,285,920 50,766,494
773.70 2,625,664 1,303,945 52,070,439
774.20 2,661,650 1,321,829 53,392,268
774.70 2,697,461 1,339,778 54,732,046
775.20 2,733,008 1,357,617 56,089,663
775.70 2,767,910 1,375,230 57,464,892
776.20 2,803,477 1,392,847 58,857,739
Device Routing Invert Outlet Devices
#1 Primary 716.40'30.0" Round 30" RCP
L= 352.0' RCP, square edge headwall, Ke= 0.500
Inlet / Outlet Invert= 716.40' / 712.90' S= 0.0099 '/' Cc= 0.900
n= 0.013, Flow Area= 4.91 sf
#2 Device 1 736.20'22.5" W x 18.0" H Vert. Riser Orifice C= 0.600
#3 Device 1 748.20'90.0" W x 15.0" H Vert. Riser Weirs X 2.00 C= 0.600
#4 Secondary 757.40'Emergency Spillway, Cv= 3.10 (C= 3.88)
Head (feet) 0.00 2.00 4.00 6.00 8.00
Width (feet) 150.00 164.00 178.00 192.00 206.00
Primary OutFlow Max=0.00 cfs @ 5.00 hrs HW=0.00' TW=706.00' (Fixed TW Elev= 706.00')
1=30" RCP ( Controls 0.00 cfs)
2=Riser Orifice ( Controls 0.00 cfs)
3=Riser Weirs ( 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-052 Town Fork Creek WS Dam #14A
Rainfall not specifiedSTOKE-052
Printed 10/23/2020Prepared by HDR, Inc
Page 4HydroCAD® 10.00-25 s/n 07102 © 2019 HydroCAD Software Solutions LLC
Stage-Discharge for Pond 1P: STOKE-052 Town Fork Creek WS Dam #14A
Elevation
(feet)
Discharge
(cfs)
Primary
(cfs)
Secondary
(cfs)
736.20 0.00 0.00 0.00
736.60 1.52 1.52 0.00
737.00 4.31 4.31 0.00
737.40 7.91 7.91 0.00
737.80 11.99 11.99 0.00
738.20 14.90 14.90 0.00
738.60 17.24 17.24 0.00
739.00 19.28 19.28 0.00
739.40 21.11 21.11 0.00
739.80 22.79 22.79 0.00
740.20 24.36 24.36 0.00
740.60 25.83 25.83 0.00
741.00 27.21 27.21 0.00
741.40 28.53 28.53 0.00
741.80 29.79 29.79 0.00
742.20 31.00 31.00 0.00
742.60 32.17 32.17 0.00
743.00 33.29 33.29 0.00
743.40 34.37 34.37 0.00
743.80 35.43 35.43 0.00
744.20 36.45 36.45 0.00
744.60 37.44 37.44 0.00
745.00 38.41 38.41 0.00
745.40 39.35 39.35 0.00
745.80 40.27 40.27 0.00
746.20 41.18 41.18 0.00
746.60 42.06 42.06 0.00
747.00 42.92 42.92 0.00
747.40 43.77 43.77 0.00
747.80 44.60 44.60 0.00
748.20 45.41 45.41 0.00
748.60 58.40 58.40 0.00
749.00 81.45 81.45 0.00
749.40 105.30 105.30 0.00
749.80 105.92 105.92 0.00
750.20 106.53 106.53 0.00
750.60 107.14 107.14 0.00
751.00 107.75 107.75 0.00
751.40 108.35 108.35 0.00
751.80 108.95 108.95 0.00
752.20 109.55 109.55 0.00
752.60 110.14 110.14 0.00
753.00 110.73 110.73 0.00
753.40 111.32 111.32 0.00
753.80 111.91 111.91 0.00
754.20 112.49 112.49 0.00
754.60 113.07 113.07 0.00
755.00 113.64 113.64 0.00
755.40 114.21 114.21 0.00
755.80 114.78 114.78 0.00
756.20 115.35 115.35 0.00
Elevation
(feet)
Discharge
(cfs)
Primary
(cfs)
Secondary
(cfs)
756.60 115.91 115.91 0.00
757.00 116.48 116.48 0.00
757.40 117.03 117.03 0.00
757.80 265.73 117.59 148.14
758.20 540.26 118.14 422.12
758.60 899.88 118.69 781.19
759.00 1,330.74 119.24 1,211.50
759.40 1,825.19 119.79 1,705.40
759.80 2,378.27 120.33 2,257.94
760.20 2,986.54 120.87 2,865.67
760.60 3,647.43 121.41 3,526.02
761.00 4,358.99 121.95 4,237.04
761.40 5,119.68 122.48 4,997.20
761.80 5,928.29 123.01 5,805.27
762.20 6,783.81 123.54 6,660.27
762.60 7,685.45 124.07 7,561.38
763.00 8,632.52 124.59 8,507.93
763.40 9,624.48 125.12 9,499.37
763.80 10,660.87 125.64 10,535.23
764.20 11,741.30 126.15 11,615.14
764.60 12,865.45 126.67 12,738.78
765.00 14,033.07 127.18 13,905.89
765.40 15,243.94 127.70 15,116.25
765.80 16,294.84 128.20 16,166.64
766.20 17,217.37 128.71 17,088.66
766.60 18,068.02 129.22 17,938.80
767.00 18,866.23 129.72 18,736.51
767.40 19,622.87 130.22 19,492.64
767.80 20,345.04 130.72 20,214.32
768.20 21,037.82 131.22 20,906.60
768.60 21,705.00 131.72 21,573.29
769.00 22,349.58 132.21 22,217.36
769.40 22,973.93 132.70 22,841.22
769.80 23,580.02 133.20 23,446.82
770.20 24,169.50 133.68 24,035.81
770.60 24,743.76 134.17 24,609.59
771.00 25,304.01 134.66 25,169.35
771.40 25,851.28 135.14 25,716.14
771.80 26,386.49 135.62 26,250.87
772.20 26,910.44 136.10 26,774.34
772.60 27,423.85 136.58 27,287.27
773.00 27,927.36 137.06 27,790.30
773.40 28,421.54 137.53 28,284.00
773.80 28,906.91 138.01 28,768.90
774.20 29,383.94 138.48 29,245.46
774.60 29,853.07 138.95 29,714.12
775.00 30,314.68 139.42 30,175.26
775.40 30,769.14 139.88 30,629.25
775.80 31,216.77 140.35 31,076.43
776.20 31,657.90 140.81 31,517.08