WILKE-029 Final Report

DAM HYDRAULIC CAPACITY
ASSESSMENT REPORT
(DRAFT)
KOA CAMPGROUND DAM
WILKE-029
WILKES 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 KOA Campground Dam in Wilkes 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, and 500 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 =
325.7
273.1
281.6
290.3
299.0
307.8
316.7
1884.7
1885.2
1885.7
1886.2
1886.7
ELEVATION
1882.2
1882.7
1883.2
1883.7
1884.2
30.5
35.3
40.2
STORAGE (ACRE-FT)
0.0
4.0
8.1
12.4
16.7
21.2
25.8
1866.2
1863.2
1863.7
1864.2
1864.7
1865.2
1865.7
1861.7
1870.2
ELEVATION
1861.7
1862.2
1862.7
STORAGE (ACRE-FT)
248.0
256.3
264.6
51.14
50
SCS Type 2
SPILLWAY
Primary
Auxiliary
TYPE
Riser / Barrel
Grass Lined Trapezoidal Channel
ELEVATION
24 HOUR - 200 YEAR EVENT, 10 INCHES, ELEVATION 1873.2 (2.9 FT FREE-BOARD)
24 HOUR - 100 YEAR EVENT, 8.83 INCHES, ELEVATION 1871.1 (5 FT FREE-BOARD)
24 HOUR - 50 YEAR EVENT, 7.76 INCHES, ELEVATION 1868.3 (7.8 FT FREE-BOARD)
24 HOUR - 25 YEAR EVENT, 6.76 INCHES, ELEVATION 1866 (10.1 FT FREE-BOARD)
SUMMARY OF INPUT PARAMETERS
1.52
SUMMARY SHEET OF HYDRAULIC CAPACITY RESULTS
KOA CAMPGROUND DAM, WILKE-029
ANALYSIS PERFORMED BY: S. MURPHY, HDR
24 HOUR - 1000 YEAR EVENT, 13.1 INCHES, ELEVATION 1876.8 (0.7 FT OVER-TOPPED)
TOP OF DAM ELEVATION = 1876.1
24 HOUR - 500 YEAR EVENT, 11.7 INCHES, ELEVATION 1875.5 (0.6 FT FREE-BOARD)
WILKE-029KOA CAMPGROUND DAM NOVEMBER 23, 2020
647.1
NOT TO SCALE
574.7
586.4
598.3
610.3
622.5
634.7
506.4
517.5
528.7
540.0
551.5
563.0
442.1
452.6
463.2
473.8
484.6
495.5
381.7
391.5
401.4
411.4
421.6
431.8
334.8
343.9
353.2
362.6
372.1
1899.7
1900.2
1900.7
1901.2
1901.7
1896.7
1897.2
1897.7
1898.2
1898.7
1899.2
1893.7
1894.2
1894.7
1895.2
1895.7
1896.2
1890.7
1891.2
1891.7
1892.2
1892.7
1893.2
1887.7
1888.2
1888.7
1889.2
1889.7
1890.2
1887.2
215.9
223.8
231.7
239.8
170.9
178.1
185.4
192.9
200.4
208.1
130.7
137.1
143.6
150.2
156.9
163.8
93.9
99.8
105.8
111.9
118.1
124.3
60.5
65.8
71.2
76.7
82.4
88.1
45.1
50.2
55.3
1881.2
1881.7
1878.2
1878.7
1879.2
1879.7
1880.2
1880.7
1875.2
1875.7
1876.2
1876.7
1877.2
1877.7
1872.2
1872.7
1873.2
1873.7
1874.2
1874.7
1869.2
1869.7
1870.2
1870.7
1871.2
1871.7
1866.7
1867.2
1867.7
1868.2
1868.7
WILKE-029KOA CAMPGROUND DAM NOVEMBER 23, 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
KOA Campgr ound Dam - WILKE-029 - Watershed Boundary
Legend
Longest FlowPath
Watershed Bound ary
0 0.5 10.25 Miles
Date: 11/19/2020
/Drainage Area: 1.52 Square MilesFlowpath Length: 2.3 Miles

APPENDIX B

Lag Time Calculation
Dam No:WILKE-029 Date:11/19/2020
Dam Name:KOA Campground Dam 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 =51.1429 from NRCS CN Calculation
S =9.55307 in.
Mean Basin Slope Y =35.392 %from Watershed Mean slope
Longest Flowpath:2.25 mi.from Watershed Longest flowpath
Flow Length l =11880 ft.
Time of Concentration Tc =1.40 Hours Tc =84 mins
Lag Time TL =0.84 Hours TL =50 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 15080 100 1508019 0 100 0 0 100 0 256187 100 25618678
Developed, Open Space Open space - Fair condition (grass cover 50% to 75%)567650 49 27814853 517106 69 35680337 0 79 0 4781 84 401641
Developed, Low Intensity Residential districts by average lot size: 1/3 acre 19376 57 1104440 13363 72 962168 0 81 0 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 9049670 36 325788108 12407931 60 744475867 0 73 0 1240643 79 98010760
Evergreen Forest Woods - Fair 3535134 36 127264822 2226228 60 133573666 0 73 0 171588 79 13555479
Mixed Forest Woods - Fair 5468627 36 196870586 4329836 60 259790172 0 73 0 591096 79 46696584
Shrub/Scrub Brush - Fair 1085 35 37978 9053 56 506995 0 70 0 9238 77 711298
Herbaceuous Herbaceuous - Fair 1122396 60 67343765 662708 71 47052288 0 81 0 44032 89 3918836
Hay/Pasture Pasture - Fair 0 49 0 154242 69 10642666 0 79 0 0 84 0
Cultivated Crops Row crops (SR + CR) - Poor 0 71 0 0 80 0 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=51.14
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): Millers Creek, North Carolina USA
Station Name: -
Latitude: 36.278236°
Longitude: -81.361906°
Elevation (USGS): 2316.9 ft
PRECIPITATION FREQUENCY ESTIMATES
by
duration
for ARI
(years):1 2 5 10 25 50 100 200 500 1000
5-min:0.352 0.418 0.494 0.555 0.637 0.699 0.765 0.832 0.923 0.998
10-min:0.562 0.669 0.791 0.887 1.01 1.11 1.22 1.32 1.46 1.57
15-min:0.703 0.841 1 1.12 1.29 1.41 1.54 1.66 1.84 1.97
30-min:0.963 1.16 1.42 1.63 1.91 2.12 2.35 2.59 2.93 3.2
60-min:1.2 1.46 1.82 2.12 2.54 2.88 3.24 3.63 4.2 4.67
2-hr:1.4 1.7 2.16 2.53 3.07 3.53 4.02 4.56 5.37 6.06
3-hr:1.52 1.85 2.33 2.73 3.32 3.82 4.36 4.97 5.86 6.64
6-hr:1.94 2.36 2.95 3.43 4.13 4.72 5.34 6.03 7.04 7.89
12-hr:2.49 3.01 3.72 4.27 5.03 5.64 6.27 6.94 7.89 8.69
24-hr:3.06 3.71 4.72 5.56 6.76 7.76 8.83 10 11.7 13.1
2-day:3.66 4.42 5.61 6.59 8.01 9.22 10.5 11.9 14 15.7
3-day:3.92 4.73 5.95 6.95 8.39 9.59 10.9 12.3 14.3 15.9
4-day:4.18 5.03 6.29 7.31 8.76 9.96 11.2 12.6 14.5 16.1
7-day:4.8 5.75 7.07 8.13 9.63 10.9 12.1 13.5 15.4 16.9
10-day:5.51 6.57 7.93 9 10.5 11.6 12.8 14 15.7 17.2
20-day:7.31 8.65 10.3 11.6 13.4 14.8 16.2 17.7 19.8 21.4
30-day:9 10.6 12.4 13.9 15.8 17.3 18.8 20.2 22.2 23.7
45-day:11.4 13.3 15.3 16.9 19 20.7 22.3 23.8 25.9 27.5
60-day:13.6 15.9 18.1 19.9 22.1 23.8 25.5 27.1 29.1 30.6
Date/time (GMT): Thu Nov 19 16:13:02 2020
pyRunTime: 0.0463089942932

APPENDIX F
Outlet Works Rating Curves

Total outlet discharge from the spillway system
Client:NCEM Date:11/16/2020
Project:Overtopping Study Engineer:T.Carter
Dam:KOA Campground Dam Dam No.WILKE-029
Reservior Water
Level (RWS)
Elevation (ft)
Primary spillway
discharge (cfs)
Emergency spillway
discharge (cfs)
Total discharge from the
spillway system (cfs)
1861.7 0.0 0.0 0.0
1862.2 20.7 0.0 20.7
1862.7 58.4 0.0 58.4
1863.2 107.4 0.0 107.4
1863.7 163.7 0.0 163.7
1864.2 183.0 0.0 183.0
1864.7 200.4 0.0 200.4
1865.2 216.5 0.0 216.5
1865.7 231.4 0.0 231.4
1866.2 245.5 0.0 245.5
1866.7 258.8 0.0 258.8
1867.2 264.2 0.0 264.2
1867.7 265.9 0.0 265.9
1868.2 267.5 0.0 267.5
1868.7 269.1 0.0 269.1
1869.2 270.7 0.0 270.7
1869.7 272.3 0.0 272.3
1870.2 273.9 0.0 273.9
1870.7 275.5 12.2 287.6
1871.2 277.0 36.1 313.1
1871.7 278.6 69.3 347.9
1872.2 280.1 111.3 391.4
1872.7 281.7 162.0 443.7
1873.2 283.2 221.4 504.6
1873.7 284.7 289.6 574.4
1874.2 286.2 366.9 653.1
1874.7 287.7 453.3 741.0
1875.2 289.2 549.1 838.3
1875.7 290.7 654.4 945.1
1876.2 292.2 769.5 1061.7
1876.7 293.7 894.6 1188.3
1877.2 295.1 1029.9 1325.1
1877.7 296.6 1175.6 1472.2
1878.2 298.1 1331.8 1629.9
1878.7 299.5 1498.9 1798.4
1879.2 300.9 1677.0 1977.9
1879.7 302.4 1866.2 2168.6
1880.2 303.8 2066.9 2370.7
1880.7 305.2 2279.1 2584.3
1881.2 306.6 2503.1 2809.7
1881.7 308.0 2739.1 3047.1
1882.2 309.4 2987.2 3296.6
1882.7 310.8 3247.6 3558.4
1883.2 312.2 3520.6 3832.8
1883.7 313.6 3806.2 4119.8
1884.2 315.0 4104.7 4419.7
1884.7 316.3 4416.3 4732.7
1885.2 317.7 4741.1 5058.8
1885.7 319.1 5079.3 5398.4
1886.2 320.4 5431.0 5751.5
1886.7 321.8 5796.5 6118.3
1887.2 323.1 6175.9 6499.0
0.0
1000.0
2000.0
3000.0
4000.0
5000.0
6000.0
7000.0
1860.0 1865.0 1870.0 1875.0 1880.0 1885.0 1890.0Total discharge from the spillway system (cfs)Reservior Water Level (RWS) Elevation (ft)
The whole spillway system rating curve (cfs)