SURRY-032 Final Report

DAM HYDRAULIC CAPACITY
ASSESSMENT REPORT
(DRAFT)
STEWARTS CREEK W/S DAM #1A
SURRY-032
SURRY COUNTY, NC
PREPARED BY:
WOOD E&I Solutions
2020
EXECUTIVE SUMMARY
A hydraulic capacity analysis was completed for the Stewarts Creek Water Supply Dam #1A in
Surry 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 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 =
3672.9
3761.8
3851.7
1312.0
1312.5
1313.0
1313.5
3244.0
1314.0
1314.5
1315.0
1315.5
3327.8
3585.1
1288.0
1288.5
1290.0
1290.5
1291.0
1285.5
1286.0
1286.5
1287.0
1287.5
1289.0
1289.5
2839.7
2918.6
261.7
301.8
51.0
1283.0 0.0
1283.5
1284.5
1285.0
2460.8
2534.5
2609.2
2685.0
1307.0
1307.5
1308.0
1308.5
1309.0
1309.5
1310.0
1310.5
1311.0
1311.5
2761.8
SUMMARY SHEET OF HYDRAULIC CAPACITY RESULTS
STEWARTS CREEK WATER SUPPLY DAM #1A, SURRY‐032
SPILLWAY
ANALYSIS PERFORMED BY:  EKENE OKORIE, WOOD
24 HOUR ‐ 1000 YEAR EVENT, 10.5 INCHES, ELEVATION 1310.0 (5.5 FT FREEBOARD)
24 HOUR ‐ 500 YEAR EVENT, 9.48 INCHES, ELEVATION 1309.2 (6.3 FT FREEBOARD)
24 HOUR ‐ 200 YEAR EVENT, 8.21 INCHES, ELEVATION 1308.0 (7.5 FT FREEBOARD)
TOP OF DAM ELEVATION  = 1315.5
Principal
24 HOUR ‐ 100 YEAR EVENT, 7.31 INCHES, ELEVATION 1304.3 (11.2 FT FREEBOARD)
ELEVATIONTYPE
24 HOUR ‐ 50 YEAR EVENT, 6.47 INCHES, ELEVATION 1300.7 (14.8 FT FREEBOARD)
24 HOUR ‐ 25 YEAR EVENT, 5.68 INCHES, ELEVATION 1297.1 (18.4 FT FREEBOARD)
SUMMARY OF INPUT PARAMETERS
SCS  Type 2
14.25
64.14
121
Riser/barrel 1283.0
STORAGE (ACRE‐FT)ELEVATION ELEVATION STORAGE (ACRE‐FT)
Auxiliary Concrete trapezoidal weir
1284.0
1308.0
2998.5
3079.4
3161.2
3412.6
3498.4
1291.5
23.8
81.0
113.5
148.4
184.8
222.7
342.7
384.4
426.8
469.9
513.7
558.0
603.0
648.6
STEWARTS CREEK WATER SUPPLY DAM #1A SURRY‐032 August 14, 2020
1328.5
1329.0
1329.5
1330.0
4222.4
5546.9
5656.6
5767.6
5879.7
5993.0
6107.6
6223.5
6340.5
6458.8
6578.2
6698.8
6820.7
6943.9
1324.0
1324.5
1325.0
1325.5
1326.0
1326.5
1327.0
1327.5
1328.01304.0
1304.5
1305.0
1305.5
1306.0
1306.5
838.2
1535.1
1594.7
1655.3
1716.8
1779.4
1843.1
1907.8
1973.6
2040.2
2107.8
2176.3
2245.9
2316.6
2388.2
1293.5
1300.0
1300.5
1301.0
1301.5
1302.0
1302.5
1303.0
1303.5
5438.4
4913.0
5015.8
5119.7
5224.8
5331.0
4414.3
4511.9
4610.7
4710.5
4811.2
1317.5
1323.5
1319.0
1319.5
1320.0
1320.5
1321.0
1318.0
1318.5
1321.5
1322.0
1322.5
1323.0
1316.0 3942.7
4034.8
4128.1
4317.81294.0
1305.9
1361.8
1418.7
1476.4
1039.2
1091.1
1143.7
1197.0
1251.0
887.4
1294.5
1295.0
1295.5
1296.0
937.3
987.9
1299.0
1299.5
1296.5
1297.0
1297.5
1298.0
1298.5
789.8
NOT TO SCALE
1316.5
1317.0
1292.0
1292.5
1293.0
695.0
742.0
STEWARTS CREEK WATER SUPPLY DAM #1A SURRY‐032 August 14, 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
Stewarts Creek Dam #1A- SURRY-032 - Watershed Boundary
Legend
Longest FlowPath
Watershed Boundary
0 0.75 1.50.375 Miles
Date: 8/12/2020
/Drainage Area: 14.25 Square Miles Flowpath Length: 8.88 Miles
APPENDIX B
Lag Time Calculation
Dam No: SURRY-032 Date: 7/27/2020
Dam Name: Stewarts Creek Water Supply Dam Engineer: E.Okorie
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 = 64.14
S =5.59089 in.
Mean Basin Slope Y = 28.273 %
Longest Flowpath: 8.88 mi.
Flow Length l =46886.4 ft.
Time of Concentration Tc = 3.37 Hours Tc = 202 mins
Lag Time TL =2.02 Hours TL =121 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.) CNOpen Water Not Available 16825 100 16825302772619 100 27726192244013 100 440126044485 100 4448451Developed, Open Space  Open space ‐ Fair condition (grass cover 50% to 75%)67583049 33115672 23391205 69 161399316594280 79 74481362315663 84 194515728Developed, Low Intensity Residential districts by average lot size: 1/3 acre 6285 57 3582541799165 72 1295398790 81 0 15691086 13494259Developed, Medium Intensity Residential districts by average lot size: 1/8 acre 0 77 0 38157 85 3243379 0 90 0 0 92 0Developed, High Intensity Urban districts ‐ Commercial and business089 0 092 0 094 0 095 0Barren Land Newly graded areas 0 77 0 158735 86 136512512438 91 221838 5997 94 563679Deciduous Forest Woods ‐ Fair4543892 36 16358010118478458960 11087075324940913 73 6868665431540382 79 2491690205Evergreen Forest Woods ‐ Fair62046 36 2233659 695463060 41727782918787 73 1371463 238869479 188706860Mixed Forest Woods ‐ Fair1173223 36 4223603765992565 60 3959553928496448 73 36240693 10643342 79 840824057Shrub/Scrub Brush ‐ Fair164029 35 5741005 773495656 4331575580 70 0 979612 77 75430152Herbaceuous Herbaceuous ‐ Fair114091 60 68454744336643 71 3079016657290 81 590522 50243089 44716298Hay/Pasture Pasture ‐ Fair1759852 49 862327293215104069 2218421778210955 79 166654767429275 84 624059111Cultivated Crops Row crops  (SR + CR) ‐ Poor0 71 0 715318 80 572254760 87 0 59899 90 5390943Woody Wetlands Not Available 0 80 0 0 85 0 0 90 0 0 95 0Emergent Herbaceuous Wetlands Not Available 0 80 0 0 85 0 0 90 0 0 95 0 Weighted CN= 64.14NOTE: 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 accurateNOTE: double‐check the exported attribute table has the same table format as the "Export_Output" table
APPENDIX D
Hyetograph Results Used for Analyses
0.02.04.06.08.010.012.00123456789101112131415161718192021222324Cumulative Depth (in)Time (hrs)Hyetographs for 24-Hour SCS Type II Rainfall Distributions25YR50YR100YR200YR500YR1000YR
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): Lambsburg, Virginia USA
Station Name: ‐
Latitude: 36.5867°
Longitude: ‐80.7809°
Elevation (USGS): None None
PRECIPITATION FREQUENCY ESTIMATES
by 
duration 
for ARI 
(years):1 2 5 10 25 50 100 200 500 1000
5‐min: 0.331 0.393 0.468 0.525 0.599 0.654 0.709 0.763 0.835 0.892
10‐min: 0.528 0.629 0.75 0.84 0.954 1.04 1.13 1.21 1.32 1.4
15‐min: 0.66 0.791 0.949 1.06 1.21 1.32 1.42 1.53 1.66 1.76
30‐min: 0.905 1.09 1.35 1.54 1.79 1.99 2.18 2.38 2.65 2.85
60‐min: 1.13 1.37 1.73 2.01 2.39 2.69 3 3.33 3.8 4.17
2‐hr: 1.33 1.62 2.07 2.41 2.9 3.3 3.72 4.17 4.8 5.33
3‐hr: 1.44 1.75 2.22 2.6 3.13 3.56 4.02 4.51 5.2 5.78
6‐hr: 1.79 2.17 2.73 3.18 3.82 4.34 4.89 5.47 6.3 6.98
12‐hr: 2.21 2.67 3.33 3.86 4.59 5.18 5.8 6.44 7.37 8.13
24‐hr: 2.62 3.18 4.03 4.71 5.68 6.47 7.31 8.21 9.48 10.5
2‐day: 3.12 3.77 4.75 5.53 6.62 7.52 8.46 9.46 10.9 12
3‐day: 3.32 4.01 5.03 5.83 6.97 7.88 8.85 9.86 11.3 12.4
4‐day: 3.52 4.25 5.31 6.14 7.31 8.25 9.23 10.3 11.7 12.9
7‐day: 4.07 4.88 5.99 6.86 8.06 9.02 10 11 12.4 13.6
10‐day: 4.68 5.58 6.76 7.67 8.89 9.86 10.8 11.8 13.2 14.3
20‐day: 6.31 7.48 8.89 9.99 11.5 12.6 13.8 14.9 16.5 17.7
30‐day: 7.82 9.22 10.7 11.9 13.3 14.4 15.5 16.5 17.9 18.9
45‐day: 9.9 11.6 13.3 14.5 16.1 17.3 18.4 19.5 20.9 21.9
60‐day: 11.8 13.8 15.7 17.1 18.8 20.1 21.3 22.5 24 25.1
Date/time (GMT):  Mon Jun 22 19:05:06 2020
pyRunTime:  0.0162420272827
APPENDIX F
Outlet Works Rating Curves
Total outlet discharge from the spillway systemClient:Date: 7/16/2020Project:Engineer: E.OkorieDam:NCEMOvertopping StudyStewarts Creek Water Supply Dam #1ADam No. SURRY-032Reservior Water Level (RWS) Elevation (ft)Primary spillway discharge From Hydrocad (cfs)Emergency spillway discharge From Hydrocad (cfs)Total discharge from the spillway system (cfs)1283.0 0.0 0.0 0.01284.0 91.1 0.0 91.11285.0 256.6 0.0 256.61286.0 279.2 0.0 279.21287.0 281.8 0.0 281.81288.0 284.5 0.0 284.51289.0 287.2 0.0 287.21290.0 289.8 0.0 289.81291.0 292.4 0.0 292.41292.0 295.0 0.0 295.01293.0 297.5 0.0 297.51294.0 300.1 0.0 300.11295.0 302.6 0.0 302.61296.0 305.1 0.0 305.11297.0 307.5 0.0 307.51298.0 310.0 0.0 310.01299.0 312.4 0.0 312.41300.0 314.8 0.0 314.81301.0 317.2 0.0 317.21302.0 319.6 0.0 319.61303.0 321.9 0.0 321.91304.0 324.3 0.0 324.31305.0 326.6 0.0 326.61306.0 328.9 0.0 328.91307.0 331.2 0.0 331.21308.0 333.5 0.0 333.51309.0 335.7 1052.0 1387.71310.0 338.0 2975.5 3313.51311.0 340.2 5466.4 5806.61312.0 342.4 8416.0 8758.41313.0 344.6 11761.7 12106.41314.0 346.8 15461.2 15808.01315.0 349.0 19483.3 19832.31316.0 351.2 23804.0 24155.21317.0 353.3 28404.0 28757.31318.0 355.4 33267.2 33622.61319.0 357.6 38380.0 38737.61320.0 359.7 43730.8 44090.51321.0 361.8 49309.5 49671.31322.0 363.9 55107.1 55471.01323.0 365.9 61115.7 61481.61324.0 368.0 67328.0 67696.01325.0 370.0 73737.6 74107.71326.0 372.1 80338.6 80710.71327.0 374.1 87125.7 87499.81328.0 376.1 94093.7 94469.91329.0 378.1 101238.3 101616.41330.0 380.1 108555.0 108935.10.020000.040000.060000.080000.0100000.0120000.01280.01290.01300.01310.01320.01330.01340.0Total discharge from the spillway system (cfs)Reservior Water Level (RWS) Elevation (ft)The whole spillway system rating curve (cfs)