STOKE-016 Final Report

DAM HYDRAULIC CAPACITY
ASSESSMENT REPORT
(DRAFT)
HANGING ROCK STATE PARK DAM
STOKE-016
STOKES COUNTY, NC
PREPARED BY:
WOOD E&I Solutions
2020
EXECUTIVE SUMMARY
A hydraulic capacity analysis was completed for the Hanging Rock State Park Dam 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. 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 the structure is hydraulically adequate for the 25
years, 50 years, 100 years, 200 years, and 500 years rainfall events. Results of the analyses
indicate the structure is over-topped by the 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 =
SUMMARY OF INPUT PARAMETERS
0.71
SUMMARY SHEET OF HYDRAULIC CAPACITY RESULTS
HANGING ROCK STATE PARK DAM, STOKE-016
ANALYSIS PERFORMED BY: SURBHI THAKUR, WOOD
24 HOUR - 200 YEAR EVENT, 9.94 INCHES, ELEVATION 1692.6 (1.4 FT FREE-BOARD)
24 HOUR - 100 YEAR EVENT, 8.75 INCHES, ELEVATION 1692 (2 FT FREE-BOARD)
24 HOUR - 50 YEAR EVENT, 7.66 INCHES, ELEVATION 1691.5 (2.5 FT FREE-BOARD)
24 HOUR - 25 YEAR EVENT, 6.66 INCHES, ELEVATION 1691 (3 FT FREE-BOARD)
24 HOUR - 1000 YEAR EVENT, 13.1 INCHES, ELEVATION 1694 (0 FT FREE-BOARD)
TOP OF DAM ELEVATION = 1694
24 HOUR - 500 YEAR EVENT, 11.7 INCHES, ELEVATION 1693.4 (0.6 FT FREE-BOARD)
1689
NA
ELEVATION
1689.0
1689.5
1690.0
60.63
42
SCS Type 2
SPILLWAY
Primary
Auxiliary
TYPE
Concrete Ogee Spillway
NONE
ELEVATION
STORAGE (ACRE-FT)
0.0
6.4
12.9
19.6
1693.5
1694.0
1694.5
1695.0
1690.5
1691.0
1691.5
1692.0
1692.5
1693.0
71.3
79.3
87.6
96.0
104.7
113.5
26.5
33.5
40.7
48.1
55.7
63.4
STORAGE (ACRE-FT)
161.0
171.2
181.5
192.0
202.8
213.8
1704.5
1705.0
1701.5
1702.0
1702.5
1703.0
1703.5
1704.0
ELEVATION
1699.0
1699.5
1700.0
1700.5
1701.0
224.9
236.3
247.9
259.7
271.7
284.0
1707.5
1708.0
1708.5
1705.5
1706.0
1706.5
1707.0
376.5
390.8
NOT TO SCALE
296.4
309.1
322.1
335.3
348.7
362.5
122.6
131.9
141.4
151.1
1696.5
1697.0
1697.5
1698.0
1698.5
1695.5
1696.0
HANGING ROCK STATE PARK DAM STOKE-016 SEPTEMBER 18, 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
Hanging Rock State Park Dam- STOKE-016 - Watershed Boundary
Legend
Longest Flowpath
Watershed
0 0.25 0.50.125 Miles
Date: 9/10/2020
/Drainage Area: 0.71 Square Miles Flowpath Length: 1.89 Miles
APPENDIX B
Lag Time Calculation
Dam No:Stoke-016 Date:7/15/2020
Dam Name:Hanging Rock State Park Dam Engineer:S. Thakur
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 =60.63
S =6.49349 in.
Mean Basin Slope Y =23.5503 %
Longest Flowpath:1.88848 mi.
Flow Length l =9971.19 ft.
Time of Concentration Tc =1.17 Hours Tc =70 mins
Lag Time TL =0.70 Hours TL =42 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 417824 100 41782415 37385 100 3738512 0 100 0
Developed, Open Space Open space - Fair condition (grass cover 50% to 75%)0 49 0 2870 69 198017 350604 79 27697702 0 84 0
Developed, Low Intensity Residential districts by average lot size: 1/3 acre 0 57 0 6795 72 489216 32112 81 2601088 0 86 0
Developed, Medium Intensity Residential districts by average lot size: 1/8 acre 0 77 0 0 85 0 16346 90 1471127 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 3693763 36 132975475 2990286 60 179417133 5711799 73 416961341 0 79 0
Evergreen Forest Woods - Fair 94035 36 3385265 43946 60 2636782 734886 73 53646653 0 79 0
Mixed Forest Woods - Fair 1879146 36 67649253 800324 60 48019452 2960115 73 216088359 0 79 0
Shrub/Scrub Brush - Fair 0 35 0 0 56 0 0 70 0 0 77 0
Herbaceuous Herbaceuous - Fair 0 60 0 0 71 0 0 81 0 0 89 0
Hay/Pasture Pasture - Fair 0 49 0 0 69 0 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=60.63
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 Analyses
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): Danbury, North Carolina USA
Station Name: -
Latitude: 36.3864°
Longitude: -80.2789°
Elevation (USGS): 1754.21 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 0.52 0.576 0.644 0.691 0.735 0.776 0.824 0.86
10-min:0.589 0.703 0.832 0.921 1.03 1.1 1.17 1.23 1.3 1.35
15-min:0.736 0.883 1.05 1.17 1.3 1.39 1.48 1.55 1.64 1.7
30-min:1.01 1.22 1.5 1.69 1.93 2.1 2.26 2.42 2.61 2.75
60-min:1.26 1.53 1.92 2.2 2.57 2.84 3.12 3.39 3.75 4.02
2-hr:1.52 1.86 2.34 2.71 3.2 3.59 3.99 4.4 4.95 5.39
3-hr:1.65 2.02 2.55 2.95 3.49 3.92 4.36 4.81 5.43 5.92
6-hr:2.06 2.5 3.15 3.67 4.37 4.95 5.55 6.17 7.06 7.78
12-hr:2.54 3.09 3.9 4.55 5.47 6.23 7.05 7.92 9.18 10.2
24-hr:3.01 3.65 4.64 5.47 6.66 7.66 8.75 9.94 11.7 13.1
2-day:3.57 4.32 5.46 6.38 7.69 8.77 9.92 11.2 12.9 14.4
3-day:3.78 4.57 5.77 6.73 8.11 9.24 10.5 11.7 13.6 15.2
4-day:3.99 4.82 6.07 7.09 8.52 9.71 11 12.3 14.3 15.9
7-day:4.54 5.45 6.76 7.82 9.31 10.5 11.8 13.2 15.2 16.8
10-day:5.17 6.19 7.58 8.7 10.3 11.5 12.8 14.2 16.1 17.7
20-day:6.99 8.31 9.98 11.3 13.1 14.5 15.9 17.3 19.3 20.8
30-day:8.64 10.2 12 13.4 15.1 16.5 17.8 19.1 20.8 22.1
45-day:10.9 12.9 14.9 16.5 18.4 19.9 21.4 22.7 24.5 25.9
60-day:13 15.2 17.5 19.1 21.2 22.8 24.3 25.7 27.6 28.9
Date/time (GMT): Thu Oct 22 18:13:56 2020
pyRunTime: 0.0154950618744

APPENDIX F
Outlet Works Rating Curves

Total outlet discharge from the spillway systemClient: NCEMDate: 9/2/2020Project: Overtopping Study Engineer: S. ThakurDam: Hanging Rock Dam Dam No. STOKE-016Reservior Water Level (RWS) Elevation (ft)Primary discharge (cfs)Total discharge from the spillway system (cfs)1689.0 0.0 0.01689.5 33.3 33.31690.0 95.5 95.51690.5 177.7 177.71691.0 277.2 277.21691.5 392.3 392.31692.0 522.2 522.21692.5 666.2 666.21693.0 824.0 824.01693.5 995.2 995.21694.0 1179.5 1179.51694.5 1376.9 1376.91695.0 1587.3 1587.31695.5 1810.5 1810.51696.0 2046.5 2046.51696.5 2295.3 2295.31697.0 2556.9 2556.91697.5 2831.3 2831.31698.0 3118.5 3118.51698.5 3418.6 3418.61699.0 3731.5 3731.51699.5 4057.3 4057.31700.0 4396.2 4396.21700.5 4748.1 4748.11701.0 5113.0 5113.01701.5 5491.1 5491.11702.0 5882.5 5882.51702.5 6287.1 6287.11703.0 6705.1 6705.11703.5 7136.5 7136.51704.0 7581.4 7581.40.01000.02000.03000.04000.05000.06000.07000.08000.01688.0 1690.0 1692.0 1694.0 1696.0 1698.0 1700.0 1702.0 1704.0 1706.0Total discharge from the spillway system (cfs)Reservior Water Level (RWS) Elevation (ft)The whole spillway system rating curve (cfs)