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Home My WebLink AboutWAKE-046 Final Report DAM HYDRAULIC CAPACITY ASSESSMENT REPORT HOLDING LAKE DAM WAKE-046 WAKE COUNTY, NC PREPARED BY: GEORGE ELLER, PE 2020 EXECUTIVE SUMMARY A hydraulic capacity analysis was completed for the Holding Lake Dam in Wake County, North Carolina. The purpose of the study was to analyze the existing potential of the dams 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 ArcGIS 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 all of the above rainfall events. The dam maintained a freeboard of 2.9 – 3.9 feet during these 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. The elevation-storage calculation does not include the storage below the normal pool elevation for this study. All elevations in this report are based on North American Vertical Datum of 1988 (NAVD88). Drainage Area (Sq. Mi.)= Curve Number = Lag Time (min.)= Rainfall Distribution Methods = N/A Principal ELEVATION 302.0 303.0 113.1 123.7 SUMMARY SHEET OF HYDRAULIC CAPACITY RESULTS HOLDING LAKE DAM, WAKE-046 173.5 160.1 274.4304.0 307.0 147.3 SPILLWAY ANALYSIS PERFORMED BY: GEORGE ELLER, PE, NCDEQ-DEMLR 24 HOUR - 1000 YEAR EVENT, 10.30 INCHES, MAX W.S. ELEVATION 300.0 (2.9 FT FREEBOARD) 24 HOUR - 500 YEAR EVENT, 9.30 INCHES, MAX W.S. ELEVATION 299.8 (3.1 FT FREEBOARD) 24 HOUR - 200 YEAR EVENT, 8.23 INCHES, MAX W.S. ELEVATION 299.5 (3.4 FT FREEBOARD) TOP OF DAM ELEVATION = 302.9 FT NAVD88 293.0 294.0 NOT TO SCALE 306.0 295.2305.0 295.0 296.0 297.0 298.0 300.0 202.9 309.0 389.3 301.0 219.1 310.0 415.7 24 HOUR - 100 YEAR EVENT, 7.45 INCHES, MAX W.S. ELEVATION 299.3 (3.6 FT FREEBOARD) ELEVATION (FT NAVD88)TYPE 24 HOUR - 50 YEAR EVENT, 6.69 INCHES, MAX W.S. ELEVATION 299.2 (3.7 FT FREEBOARD) 24 HOUR - 25 YEAR EVENT, 5.95 INCHES, MAX W.S. ELEVATION 299.0 (3.9 FT FREEBOARD) SUMMARY OF INPUT PARAMETERS NRCS-NOAA 0.19 73.13 27 364.1308.0299.0 187.8 Concrete Circular Riser-Barrel Auxiliary N/A STORAGE (ACRE-FT) 317.1 340.0 135.2 ELEVATION 298.0 STORAGE (ACRE-FT) 236.4 254.8 HOLDING LAKE DAM WAKE-046 June 11, 2020 APPENDIX A Watershed Boundary Sources: Esri, HERE, Garmin, Intermap, increment P Corp., GEBCO,USGS, FAO, NPS, NRCAN, GeoBase, IGN, Kadaster NL, OrdnanceSurvey, Esri Japan, METI, Esri China (Hong Kong), (c) OpenStreetMapcontributors, and the GIS User Community Holding Lake Dam - WAKE-046 - Watershed Boundar y .Drainage Area: 0.19 Square MilesFlowpath Length: 3,997 Feet Legend Watershed Boundary Longest Flowpath 0 0.25 0.50.125 Miles APPENDIX B Time of Concentration Calculation Dam No:WAKE-046 Date:8/8/2018 Dam Name:Holding Lake Dam Engineer:G. Eller 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 =73.13 from StreamStats S =3.67428 in. Mean Basin Slope Y =6.93 %from StreamStats Longest Flowpath:0.757 mi.from StreamStats Flow Length l =3996.96 ft. Time of Concentration Tc =0.75 Hours Tc =45 mins Lag Time TL =0.45 Hours TL =27 mins APPENDIX C NRCS Curve Number Summary Sheet Change CN according to TR-55 (see tables below) HSG Type A CN B CN C CN D CN Open Water 1425.3736 100 142537.3591 3788.7322 100 378873.2196 0.0000 100 0 601749.0279 100 60174903 Developed, Open Space 0.0000 68 0 396403.7606 79 31315897.09 0.0000 86 0 13972.1199 89 1243519 Developed, Low Intensity 21292.9401 57 1213697.585 437444.7154 72 31496019.51 0.0000 81 0 17791.5643 86 1530075 Developed, Medium Intensity 9640.5108 77 742319.3295 208098.3453 85 17688359.35 0.0000 90 0 6997.2338 92 643745.5 Developed, High Intensity 0.0000 89 0 6630.1846 92 609976.9842 0.0000 94 0 0.0000 95 0 Barren Land 0.0000 77 0 920.5037 86 79163.31637 0.0000 91 0 0.0000 94 0 Deciduous Forest 49167.99406 36 1770047.786 101798.7882 60 6107927.289 0 73 0 178907.5209 79 14133694 Evergreen Forest 16093.4458 36 579364.0475 40630.3644 60 2437821.862 0.0000 73 0 100430.1945 79 7933985 Mixed Forest 63567.2474 36 2288420.905 98251.2313 60 5895073.88 0.0000 73 0 66752.7358 79 5273466 Shrub/Scrub 0.0000 35 0 0.0000 56 0 0.0000 70 0 0.0000 77 0 Herbaceuous 0.0000 50 0 114019.8213 71 8095407.31 0.0000 81 0 0.0000 89 0 Hay/Pasture 396781.0833 49 19442273.08 1924008.623 69 132756595 0 79 0 245335.9624 84 20608221 Cultivated Crops 0.0000 71 0 0.0000 80 0 0.0000 87 0 0.0000 90 0 designed by dan.k Woody Wetlands 0.0000 80 0 0.0000 85 0 0.0000 90 0 0.0000 95 0 Emergent Herbaceuous Wetlands 0.0000 80 0 0.0000 85 0 0.0000 90 0 0.0000 95 0 Weighted CN=73.13 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. Hydrologic Condition assumed as "Fair" 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 0 2 4 6 8 10 12 14 16 18 20 22 24Cumulative Inches of RainHours Hyetographs for 24-Hour 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): North Carolina Station Name: - Latitude: 35.9570° Longitude: -78.5090° Elevation (USGS): 298.83 ft PRECIPITATION FREQUENCY ESTIMATES by duration for ARI (years):1 2 5 10 25 50 100 200 500 1000 5-min:0.403 0.468 0.535 0.599 0.664 0.714 0.759 0.799 0.842 0.881 10-min:0.643 0.749 0.857 0.958 1.06 1.14 1.21 1.27 1.33 1.39 15-min:0.804 0.942 1.08 1.21 1.34 1.44 1.53 1.6 1.68 1.74 30-min:1.1 1.3 1.54 1.76 1.99 2.17 2.34 2.49 2.67 2.82 60-min:1.37 1.63 1.97 2.29 2.65 2.94 3.22 3.49 3.83 4.12 2-hr:1.61 1.92 2.34 2.74 3.21 3.62 4.02 4.42 4.93 5.38 3-hr:1.7 2.03 2.49 2.94 3.48 3.96 4.43 4.92 5.58 6.16 6-hr:2.05 2.44 2.99 3.53 4.2 4.8 5.4 6.03 6.87 7.64 12-hr:2.41 2.88 3.55 4.21 5.05 5.81 6.57 7.39 8.52 9.55 24-hr:2.86 3.45 4.33 5.02 5.95 6.69 7.45 8.23 9.3 10.1 2-day:3.32 4 4.97 5.73 6.76 7.57 8.4 9.25 10.4 11.3 3-day:3.52 4.23 5.23 6.02 7.09 7.94 8.81 9.69 10.9 11.9 4-day:3.72 4.46 5.49 6.31 7.43 8.31 9.21 10.1 11.4 12.4 7-day:4.31 5.14 6.25 7.14 8.35 9.31 10.3 11.3 12.7 13.8 10-day:4.9 5.83 7 7.93 9.17 10.1 11.1 12.1 13.5 14.5 20-day:6.57 7.76 9.17 10.3 11.8 13 14.2 15.4 17 18.3 30-day:8.16 9.59 11.2 12.4 14 15.2 16.4 17.6 19.3 20.5 45-day:10.4 12.2 13.9 15.3 17.1 18.4 19.7 21 22.7 24 60-day:12.5 14.6 16.4 17.9 19.8 21.2 22.6 23.9 25.6 26.9 Date/time (GMT): Mon Apr 16 12:45:10 2018 pyRunTime: 0.0400829315186 APPENDIX F Outlet Works Rating Curves Primary Spillway:Concrete Circular Riser/Barrel Emergency Spillway:N/A Top of Dam :302.9 ft NAVD88 Normal Pool :298.0 ft NAVD88 RWS Elevation (ft NAVD88) Primary Spillway Discharge (cfs) Emergency Spillway Discharge (cfs) Total Structure Discharge (cfs) 298.0 0 0 0 298.5 19 0 19 299.0 58 0 58 299.5 109 0 109 300.0 162 0 162 300.5 181 0 181 301.0 199 0 199 301.5 215 0 215 302.0 230 0 230 302.5 244 0 244 303.0 257 0 257 303.5 263 0 263 304.0 265 0 265 304.5 267 0 267 305.0 269 0 269 305.5 271 0 271 306.0 273 0 273 306.5 274 0 274 307.0 276 0 276 307.5 278 0 278 308.0 280 0 280 SPILLWAY ASSESSMENT Holding Lake Dam, WAKE-046 298 299 300 301 302 303 304 305 306 307 308 309 0 100 200 300RWS Elevation (feet NAVD88)Spillway Discharge (cfs) Spillway Discharge Capacity Primary Spillway:Emergency Spillway:Total Structure