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Home My WebLink AboutSTOKE-120 Final ReportDAM HYDRAULIC CAPACITY ASSESSMENT REPORT (DRAFT) BELEWS CREEK HOLDING BASIN DAM STOKE-120 STOKES COUNTY, NC PREPARED BY: WOOD E&I Solutions 2020 EXECUTIVE SUMMARY A hydraulic capacity analysis was completed for the Belews Creek Holding Basin 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, 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 = NOT TO SCALE STORAGE (ACRE‐FT) 6.6 9.0 11.5 ELEVATION 802.0 803.0 804.0 STORAGE (ACRE‐FT) 0.0 2.1 4.3801.0 98 3.6 SCS Type 2 SPILLWAY Principal Auxiliary TYPE Effluent Pump Concrete Weir ELEVATION 799 801 ELEVATION 799.0 800.0 0.0052 SUMMARY SHEET OF HYDRAULIC CAPACITY RESULTS BELEWS CREEK HOLDING BASIN DAM, STOKE‐120 ANALYSIS PERFORMED BY: SURBHI THAKUR, WOOD TOP OF DAM ELEVATION = 804 24 HOUR ‐ 1000 YEAR EVENT, 11.5 INCHES, ELEVATION 800.9 (3.1 FT FREE‐BOARD) 24 HOUR ‐ 500 YEAR EVENT, 10.4 INCHES, ELEVATION 800.8 (3.2 FT FREE‐BOARD) 24 HOUR ‐ 200 YEAR EVENT, 8.92 INCHES, ELEVATION 800.7 (3.3 FT FREE‐BOARD) 24 HOUR ‐ 100 YEAR EVENT, 7.92 INCHES, ELEVATION 800.6 (3.4 FT FREE‐BOARD) 24 HOUR ‐ 50 YEAR EVENT, 6.99 INCHES, ELEVATION 800.5 (3.5 FT FREE‐BOARD) 24 HOUR ‐ 25 YEAR EVENT, 6.12 INCHES, ELEVATION 800.4 (3.6 FT FREE‐BOARD) SUMMARY OF INPUT PARAMETERS BELEWS CREEK HOLDING BASIN DAM STOKE‐120 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 Belews Creek Holding Basin Dam- STOKE-120 - Watershed Boundary Legend Longest FlowPath Watershed Boundary 0 0.08 0.160.04 Miles Date: 9/17/2020 /Drainage Area: 0.0052 Square Miles Flowpath Length: 419 Feet APPENDIX B Lag Time Calculation Dam No: Stoke-120 Date: 7/15/2020 Dam Name: Belews Creek Holding Basin 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 = 98 from NRCS CN S =0.20408 in. Mean Basin Slope Y = 0 % from Holding Basin Footprint, assumed minimal slope Longest Flowpath: 0 mi. from Holding basin longitudinal Length Flow Length l = ft. Time of Concentration Tc = 0.10 Hours Tc = 6 mins <-- Direct runoff is from within the footprint of the Retention Basin Lag Time TL =0.06 Hours TL =3.6 mins Assumed Minimum Tc 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.) CNOpen Water Not Available 100 0 100 0 100 0 0 100 0Developed, Open Space Open space ‐ Fair condition (grass cover 50% to 75%) 49 0 69 0 79 0 0 84 0Developed, Low Intensity Residential districts by average lot size: 1/3 acre 57 0 72 0 81 0 0 86 0Developed, Medium Intensity Residential districts by average lot size: 1/8 acre 77 0 85 0 90 0 0 92 0Developed, High Intensity Urban districts ‐ Commercial and business 89 0 92 0 94 0 0 95 0Barren Land Newly graded areas 77 0 86 0 91 0 0 94 0Deciduous Forest Woods ‐ Fair 36 0 60 0 73 0 0 79 0Evergreen Forest Woods ‐ Fair 36 0 60 0 73 0 0 79 0Mixed Forest Woods ‐ Fair 36 0 60 0 73 0 0 79 0Shrub/Scrub Brush ‐ Fair 35 0 56 0 70 0 0 77 0Herbaceuous Herbaceuous ‐ Fair 60 0 71 0 81 0 0 89 0Hay/Pasture Pasture ‐ Fair 49 0 69 0 79 0 0 84 0Cultivated Crops Row crops (SR + CR) ‐ Poor 71 0 80 0 87 0 0 90 0Woody Wetlands Not Available 80 0 85 0 90 0 0 95 0Emergent Herbaceuous Wetlands Not Available 80 0 85 0 90 0 0 95 0 Weighted CN= 98.00NOTE: Direct runoff from the watershed area bounded by the perimeter of the dam on all sides. Since the top of the dams are compacted and covered with granular surfacing, it is assumed the entire depth of rainfall on this footprint enters the basin. Hence, Curve Number is assumed to be 98. 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): Walnut Cove, North Carolina USA Station Name: - Latitude: 36.2953° Longitude: -80.0645° Elevation (USGS): 794.23 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 0.516 0.569 0.629 0.668 0.704 0.734 0.767 0.788 10-min:0.589 0.702 0.827 0.91 1 1.06 1.12 1.16 1.21 1.24 15-min:0.737 0.883 1.05 1.15 1.27 1.35 1.41 1.47 1.53 1.56 30-min:1.01 1.22 1.49 1.67 1.88 2.03 2.17 2.29 2.43 2.52 60-min:1.26 1.53 1.91 2.17 2.51 2.75 2.98 3.21 3.49 3.68 2-hr:1.5 1.82 2.28 2.63 3.08 3.42 3.76 4.1 4.54 4.87 3-hr:1.61 1.96 2.46 2.84 3.33 3.7 4.07 4.44 4.92 5.28 6-hr:1.98 2.4 3.01 3.48 4.12 4.63 5.15 5.68 6.41 6.98 12-hr:2.38 2.88 3.63 4.22 5.06 5.74 6.47 7.23 8.31 9.18 24-hr:2.84 3.43 4.34 5.07 6.12 6.99 7.92 8.92 10.4 11.5 2-day:3.33 4.01 5.03 5.84 6.97 7.9 8.87 9.9 11.3 12.5 3-day:3.52 4.24 5.31 6.16 7.36 8.34 9.36 10.4 12 13.2 4-day:3.71 4.48 5.59 6.49 7.75 8.77 9.85 11 12.6 13.9 7-day:4.25 5.09 6.27 7.22 8.55 9.62 10.7 11.9 13.6 14.9 10-day:4.82 5.75 7 8 9.39 10.5 11.6 12.8 14.5 15.8 20-day:6.5 7.71 9.22 10.4 12.1 13.3 14.6 15.9 17.7 19.1 30-day:8.05 9.5 11.1 12.4 14 15.3 16.5 17.7 19.3 20.5 45-day:10.1 11.9 13.8 15.2 17 18.4 19.8 21.1 22.7 24 60-day:12.1 14.2 16.2 17.7 19.6 21.1 22.4 23.7 25.4 26.6 Date/time (GMT): Thu Sep 10 16:05:05 2020 pyRunTime: 0.0169610977173 APPENDIX F Outlet Works Rating Curves Total outlet discharge from the spillway systemClient: NCEMDate: 9/2/2020Project: Overtopping StudyEngineer: S. ThakurDam: Belews Creek Holding Basin DamDam No. STOKE-016Reservior Water Level (RWS) Elevation (ft)Primary Spillway discharge (cfs)Emergency spillway discharge (cfs)Total discharge from the spillway system (cfs)799.0 3.6 0.0 3.6800.0 3.6 0.0 3.6801.0 3.6 0.0 3.6802.0 3.6 29.2 32.8803.0 3.6 103.8 107.4804.0 3.6 229.7 233.2805.0 3.6 413.6 417.2806.0 3.6 661.9 665.4807.0 3.6 980.3 983.8808.0 3.6 1374.2 1377.8809.0 3.6 1848.7 1852.2810.0 3.6 2408.4 2412.00.0500.01000.01500.02000.02500.03000.0798.0 800.0 802.0 804.0 806.0 808.0 810.0 812.0Total discharge from the spillway system (cfs)Reservior Water Level (RWS) Elevation (ft)The whole spillway system rating curve (cfs)