STOKE-014 Final Report

DAM HYDRAULIC CAPACITY
ASSESSMENT REPORT
(DRAFT)
LITTLE YADKIN RIVER WS DAM #12
STOKE-014
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 Little Yadkin River WS Dam #12 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 =
Primary
Auxiliary
366.8
296.1
307.3
318.7
330.4
342.3
354.4
1102.4
1102.9
1103.4
1103.9
1104.4
ELEVATION
1099.9
1100.4
1100.9
1101.4
1101.9
38.9
STORAGE (ACRE-FT)
0.0
4.0
8.0
12.2
16.4
20.8
25.2
1083.9
1080.9
1081.4
1081.9
1082.4
1082.9
1083.4
1079.4
1084.4
ELEVATION
1079.4
1079.9
1080.4
STORAGE (ACRE-FT)
263.7
274.3
285.1
29.7
34.2
SPILLWAY TYPE
Riser / Barrel
Grass Lined Trapezoidal channel
ELEVATION
SUMMARY OF INPUT PARAMETERS
0.52
24 HOUR - 200 YEAR EVENT, 9.91 INCHES, ELEVATION 1085.5 (2.1 FT FREE-BOARD)
24 HOUR - 100 YEAR EVENT, 8.73 INCHES, ELEVATION 1085 (2.6 FT FREE-BOARD)
24 HOUR - 50 YEAR EVENT, 7.65 INCHES, ELEVATION 1084.7 (2.9 FT FREE-BOARD)
24 HOUR - 25 YEAR EVENT, 6.66 INCHES, ELEVATION 1083.9 (3.7 FT FREE-BOARD)
SUMMARY SHEET OF HYDRAULIC CAPACITY RESULTS
LITTLE YADKIN RIVER WS DAM #12, STOKE-014
ANALYSIS PERFORMED BY: S. MURPHY, HDR
51.56
41
SCS Type 2
TOP OF DAM ELEVATION = 1087.6
24 HOUR - 1000 YEAR EVENT, 13.1 INCHES, ELEVATION 1087.1 (0.5 FT FREE-BOARD)
24 HOUR - 500 YEAR EVENT, 11.6 INCHES, ELEVATION 1086.3 (1.3 FT FREE-BOARD)
STOKE-014LITTLE YADKIN RIVER WS DAM #12 OCTOBER 5, 2020
862.9
NOT TO SCALE
743.7
762.9
782.4
802.1
822.1
842.4
634.6
652.0
669.8
687.8
706.1
724.8
535.3
551.1
567.2
583.7
600.4
617.3
446.2
460.4
474.8
489.5
504.5
519.7
379.4
392.2
405.3
418.7
432.3
1119.4
1114.4
1114.9
1115.4
1115.9
1116.4
1116.9
1117.4
1117.9
1118.4
1111.4
1111.9
1112.4
1112.9
1113.4
1113.9
1108.4
1107.4
1107.9
1104.9
1118.9
1108.9
1109.4
1109.9
1110.4
1110.9
1105.4
1105.9
1106.4
233.0
243.0
253.3
170.3
177.9
186.3
195.2
204.4
213.8
129.2
135.8
142.5
149.3
156.2
163.2
92.0
97.9
1106.9
116.4
122.7
58.8
64.1
69.4
74.9
80.5
86.2
223.3
43.7
48.6
53.7
1098.9
1099.4
1095.9
1096.4
1096.9
1097.4
1097.9
1098.4
1092.9
1093.4
104.0
110.1
1093.9
1094.4
1094.9
1095.4
1089.9
1090.4
1090.9
1091.4
1091.9
1092.4
1086.9
1087.4
1087.9
1088.4
1088.9
1089.4
1084.4
1084.9
1085.4
1085.9
1086.4
STOKE-014LITTLE YADKIN RIVER WS DAM #12 OCTOBER 5, 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
Little Yadkin River WS Dam #12 - STOKE-014 - Watershed Boundary
Legend
Longest FlowPath
Watershed Bound ary
0 0.35 0.70.175 Miles
Date: 10 /2/2020
/Drainage Area: 0.52 Square MilesFlowpath Length: 1.4 miles

APPENDIX B

Lag Time Calculation
Dam No:STOKE-014 Date:10/8/2020
Dam Name:Little Yadkin River WS Dam #12 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 =51.5648 from NRCS CN Calculation
S =9.39308 in.
Mean Basin Slope Y =25.1886 %from Watershed Mean slope
Longest Flowpath:1.42 mi.from Watershed Longest flowpath
Flow Length l =7497.6 ft.
Time of Concentration Tc =1.13 Hours Tc =68 mins
Lag Time TL =0.68 Hours TL =41 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 45581 100 4558091 0 100 0 312899 100 31289933
Developed, Open Space Open space - Fair condition (grass cover 50% to 75%)32623 49 1598537 254241 69 17542626 70967 79 5606418 7369 84 619020
Developed, Low Intensity Residential districts by average lot size: 1/3 acre 4252 57 242379 81932 72 5899085 0 81 0 3980 86 342273
Developed, Medium Intensity Residential districts by average lot size: 1/8 acre 0 77 0 29066 85 2470611 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 6137156 36 220937599 2913614 60 174816848 351799 73 25681301 54314 79 4290815
Evergreen Forest Woods - Fair 0 36 0 7441 60 446460 0 73 0 2248 79 177564
Mixed Forest Woods - Fair 235541 36 8479473 479432 60 28765935 39653 73 2894693 4332 79 342211
Shrub/Scrub Brush - Fair 549743 35 19241001 339401 56 19006475 0 70 0 0 77 0
Herbaceuous Herbaceuous - Fair 86639 60 5198366 50104 71 3557357 0 81 0 47342 89 4213419
Hay/Pasture Pasture - Fair 275748 49 13511670 1615357 69 111459650 213765 79 16887397 28794 84 2418665
Cultivated Crops Row crops (SR + CR) - Poor 0 71 0 126906 80 10152471 0 87 0 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=51.56
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): King, North Carolina USA
Station Name: -
Latitude: 36.368905°
Longitude: -80.364624°
Elevation (USGS): 1253.32 ft
PRECIPITATION FREQUENCY ESTIMATES
by
duration
for ARI
(years):1 2 5 10 25 50 100 200 500 1000
5-min:0.367 0.437 0.517 0.574 0.643 0.69 0.734 0.775 0.825 0.86
10-min:0.586 0.7 0.829 0.918 1.02 1.1 1.17 1.23 1.3 1.36
15-min:0.733 0.879 1.05 1.16 1.3 1.39 1.48 1.55 1.64 1.7
30-min:1.01 1.22 1.49 1.68 1.92 2.1 2.26 2.41 2.61 2.75
60-min:1.25 1.52 1.91 2.19 2.56 2.84 3.11 3.39 3.75 4.02
2-hr:1.51 1.84 2.33 2.69 3.19 3.58 3.98 4.38 4.94 5.38
3-hr:1.64 2 2.53 2.93 3.48 3.9 4.34 4.79 5.41 5.9
6-hr:2.04 2.48 3.13 3.64 4.34 4.92 5.51 6.14 7.03 7.75
12-hr:2.51 3.06 3.87 4.52 5.43 6.19 7.01 7.88 9.13 10.2
24-hr:3.01 3.65 4.65 5.47 6.66 7.65 8.73 9.91 11.6 13.1
2-day:3.58 4.33 5.47 6.39 7.69 8.76 9.91 11.1 12.9 14.4
3-day:3.79 4.58 5.77 6.74 8.11 9.23 10.4 11.7 13.6 15.1
4-day:4 4.83 6.08 7.09 8.52 9.7 11 12.3 14.2 15.8
7-day:4.55 5.46 6.77 7.82 9.29 10.5 11.8 13.1 15.1 16.6
10-day:5.19 6.21 7.6 8.71 10.2 11.5 12.8 14.1 16 17.6
20-day:7 8.32 9.98 11.3 13 14.4 15.8 17.3 19.2 20.7
30-day:8.66 10.2 12 13.4 15.1 16.4 17.7 19 20.7 21.9
45-day:10.9 12.9 14.9 16.4 18.4 19.8 21.2 22.6 24.4 25.7
60-day:13 15.2 17.4 19.1 21.2 22.7 24.2 25.6 27.4 28.8
Date/time (GMT): Thu Oct 8 21:16:05 2020
pyRunTime: 0.0172779560089

APPENDIX F
Outlet Works Rating Curves

Total outlet discharge from the spillway system
Client:NCEM Date:10/1/2020
Project:Overtopping Study Engineer:T.Carter
Dam:Little Yadkin River WS Dam #12 Dam No.STOKE-014
Reservior Water
Level (RWS)
Elevation (ft)
Primary spillway
discharge (cfs)
Emergency spillway
discharge (cfs)
Total discharge from the
spillway system (cfs)
1079.4 0.0 0.0 0.0
1079.9 3.6 0.0 3.6
1080.4 4.3 0.0 4.3
1080.9 4.3 0.0 4.3
1081.4 4.3 0.0 4.3
1081.9 4.4 0.0 4.4
1082.4 4.4 0.0 4.4
1082.9 4.5 0.0 4.5
1083.4 4.5 0.0 4.5
1083.9 4.5 0.0 4.5
1084.4 4.6 0.0 4.6
1084.9 4.6 34.6 39.3
1085.4 4.7 98.0 102.6
1085.9 4.7 180.0 184.7
1086.4 4.7 277.1 281.8
1086.9 4.8 387.2 392.0
1087.4 4.8 509.0 513.8
1087.9 4.9 641.4 646.3
1088.4 4.9 783.7 788.6
1088.9 4.9 935.1 940.0
1089.4 5.0 1095.2 1100.2
1089.9 5.0 1263.6 1268.6
1090.4 5.0 1439.7 1444.8
1090.9 5.1 1623.4 1628.4
1091.4 5.1 1814.2 1819.4
1091.9 5.1 2012.1 2017.2
1092.4 5.2 2216.6 2221.8
1092.9 5.2 2427.6 2432.8
1093.4 5.2 2644.9 2650.2
1093.9 5.3 2868.4 2873.6
1094.4 5.3 3097.8 3103.1
1094.9 5.4 3333.0 3338.3
1095.4 5.4 3573.9 3579.2
1095.9 5.4 3820.3 3825.7
1096.4 5.5 4072.1 4077.6
1096.9 5.5 4329.3 4334.7
1097.4 5.5 4591.6 4597.1
1097.9 5.6 4859.0 4864.6
1098.4 5.6 5131.5 5137.0
1098.9 5.6 5408.8 5414.4
1099.4 5.6 5691.0 5696.6
1099.9 5.7 5977.9 5983.5
1100.4 5.7 6269.4 6275.2
1100.9 5.7 6565.6 6571.3
1101.4 5.8 6866.3 6872.1
1101.9 5.8 7171.4 7177.2
1102.4 5.8 7481.0 7486.8
1102.9 5.9 7794.8 7800.7
1103.4 5.9 8113.0 8118.9
1103.9 5.9 8435.3 8441.2
1104.4 6.0 8761.8 8767.8
1104.9 6.0 9092.4 9098.4
0.0
1000.0
2000.0
3000.0
4000.0
5000.0
6000.0
7000.0
8000.0
9000.0
10000.0
1075.0 1080.0 1085.0 1090.0 1095.0 1100.0 1105.0 1110.0Total discharge from the spillway system (cfs)Reservior Water Level (RWS) Elevation (ft)
The whole spillway system rating curve (cfs)