SURRY-031 Final Report

DAM HYDRAULIC CAPACITY
ASSESSMENT REPORT
(DRAFT)

REYNOLDS LAKE DAM

SURRY-031

SURRY COUNTY, NC

PREPARED BY:
WOOD E&I Solutions

2020

EXECUTIVE SUMMARY
A hydraulic capacity analysis was completed for the Reynolds Lake Dam
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 the
25 years rainfall event. The structure is over-topped by the 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 =
1050.2
1078.6
NOT TO SCALE
1477.5
1480.0
Principal
Auxiliary
Concrete Rectangular weir
Concrete overflow weir wall
884
911.2
938.5
966.1
993.9
1022
65.47
63
2.3264
725.4
751.3
777.4
803.8
830.3
857
574.2
598.9
623.8
648.9
674.2
699.7
1497.5
1498
1498.5
1499
1499.5
1500
1494.5
1495
1495.5
1496
1496.5
1497
1491.5
1492
1492.5
1493
1493.5
1494
406.7
430
453.6
477.3
ELEVATION
1489
1489.5
1490
1490.5
1491
270.6
292.8
315.2
337.8
360.6
383.5
141.7
162.7
183.8
205.2
226.8
248.6
1488
1488.5
STORAGE (ACRE-FT)
0
19.7
39.5
59.5
79.8
100.2
120.8
1485
1485.5
1486
1486.5
1487
1487.5
1482
1482.5
1483
1483.5
1484
1484.5
1479
1479.5
1480
1480.5
1481
1481.5
ELEVATION
1477.5
1478
1478.5
STORAGE (ACRE-FT)
501.2
525.3
549.7
SCS Type 2
SPILLWAY TYPE ELEVATION
24 HOUR - 100 YEAR EVENT, 7.86 INCHES, ELEVATION 1480.8 (0.8 FT OVER-TOPPED)
24 HOUR - 50 YEAR EVENT, 6.96 INCHES, ELEVATION 1480.4 (0.4 FT OVER-TOPPED)
TOP OF DAM ELEVATION = 1480
24 HOUR - 25 YEAR EVENT, 6.11 INCHES, ELEVATION 1479.9 (0.1 FT FREE-BOARD)
SUMMARY OF INPUT PARAMETERS
SUMMARY SHEET OF HYDRAULIC CAPACITY RESULTS
REYNOLDS LAKE DAM, SURRY-031
ANALYSIS PERFORMED BY: E.OKORIE, WOOD
24 HOUR - 1000 YEAR EVENT, 11.3 INCHES, ELEVATION 1481.8 (1.8 FT OVER-TOPPED)
24 HOUR - 500 YEAR EVENT, 10.2 INCHES, ELEVATION 1481.6 (1.6 FT OVER-TOPPED)
24 HOUR - 200 YEAR EVENT, 8.81 INCHES, ELEVATION 1481.1 (1.1 FT OVER-TOPPED)
SURRY-031REYNOLDS LAKE DAM SEPTEMBER 11, 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
Reynolds Lake Dam - SURRY-031 - Watershed Boundary
Legend
Longe st Flo wPath
Wa tershe d Bou ndary
0 0.5 10.25 Miles
Date : 8/12/2020
/Drainage Area: 2.33 Square MilesFlowpath Length: 4.48 Miles
APPENDIX B
Lag Time Calculation
Dam No: SURRY-031 Date: 7/17/2020
Dam Name: Reynolds Lake 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 = 65.47
S =5.27417 in.
Mean Basin Slope Y = 32.174 %
Longest Flowpath: 4.4761 mi.
Flow Length l =23633.8 ft.
Time of Concentration Tc = 1.76 Hours Tc = 106 mins
Lag Time TL =1.06 Hours TL =63 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 WaterNot Available 6300 100 62995483164100 8316415 1480466100 1480465760 100 0Developed, Open Space  Open space ‐ Fair condition (grass cover 50% to 75%)0 49 0 3501335 69 24159209220100079 15879018084 0Developed, Low IntensityResidential districts by average lot size: 1/3 acre0 57 0 124805 72 8985968081 0 086 0Developed, Medium IntensityResidential districts by average lot size: 1/8 acre077 0 085 0 090 0 092 0Developed, High Intensity Urban districts ‐ Commercial and business 089 0 092 0 094 0 095 0Barren Land Newly graded areas 0 77 0 0 86 0 0 91 0 0 94 0Deciduous ForestWoods ‐ Fair121268736 436567441518494860 9110968721302810973 951051930919672 79 72654088Evergreen Forest Woods ‐ Fair23118 36 8322562402272 60 1441363091180159 73 86151639511 79 40365Mixed Forest Woods ‐ Fair771082 36 27758955 1627096660 976257957512010473 37376761332780079 25896186Shrub/Scrub Brush ‐ Fair0 35 0 280667 56 15717374390111 70 27307773 0 77 0Herbaceuous Herbaceuous ‐ Fair0 60 0 153708471 109132970116897 81 9468660089 0Hay/Pasture Pasture ‐ Fair0 49 0 689511 69 47576265 2510 79 198269 0 84 0Cultivated Crops Row crops  (SR + CR) ‐ Poor071 0 080 0 087 0 090 0Woody Wetlands Not Available 0 80 0 0 85 0 0 90 0 0 95 0Emergent Herbaceuous WetlandsNot Available 0 80 0 0 85 0 0 90 0 0 95 0 Weighted CN= 65.47NOTE: 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): Glade Valley, North Carolina USA
Station Name: ‐
Latitude: 36.4700°
Longitude: ‐80.9602°
Elevation (USGS): None None
PRECIPITATION FREQUENCY ESTIMATES
by 
duration 
for ARI 
(years):1 2 5 10 25 50 100 200 500 1000
5‐min: 0.337 0.401 0.478 0.539 0.62 0.683 0.748 0.814 0.905 0.979
10‐min: 0.539 0.641 0.765 0.861 0.988 1.09 1.19 1.29 1.43 1.54
15‐min: 0.673 0.806 0.968 1.09 1.25 1.38 1.5 1.63 1.8 1.94
30‐min: 0.923 1.11 1.38 1.58 1.86 2.07 2.3 2.54 2.87 3.13
60‐min: 1.15 1.4 1.76 2.06 2.47 2.81 3.17 3.56 4.11 4.58
2‐hr: 1.37 1.66 2.13 2.51 3.06 3.52 4.01 4.55 5.33 6
3‐hr: 1.48 1.81 2.31 2.72 3.31 3.81 4.35 4.93 5.8 6.53
6‐hr: 1.87 2.27 2.88 3.37 4.07 4.65 5.26 5.93 6.88 7.68
12‐hr: 2.36 2.85 3.57 4.13 4.89 5.51 6.14 6.79 7.72 8.47
24‐hr: 2.82 3.41 4.34 5.08 6.11 6.96 7.86 8.81 10.2 11.3
2‐day: 3.37 4.07 5.13 5.98 7.17 8.14 9.17 10.3 11.8 13.1
3‐day: 3.59 4.33 5.43 6.3 7.51 8.5 9.53 10.6 12.1 13.4
4‐day: 3.82 4.6 5.72 6.62 7.85 8.85 9.88 11 12.5 13.7
7‐day: 4.38 5.25 6.42 7.34 8.6 9.6 10.6 11.7 13.2 14.3
10‐day: 5.04 6.01 7.24 8.2 9.47 10.5 11.5 12.5 13.9 15
20‐day: 6.77 8.02 9.5 10.7 12.2 13.4 14.6 15.9 17.5 18.8
30‐day: 8.4 9.89 11.5 12.7 14.2 15.4 16.6 17.7 19.2 20.3
45‐day: 10.6 12.4 14.2 15.5 17.2 18.4 19.7 20.9 22.4 23.6
60‐day: 12.7 14.8 16.7 18.2 20 21.4 22.7 24 25.7 26.9
Date/time (GMT):  Mon Jun 22 18:35:31 2020
pyRunTime:  0.016058921814
APPENDIX F
Outlet Works Rating Curves
Total outlet discharge from the spillway system
Client: NC DEMLR Date: 7/16/2020
Project: Overtopping Study Engineer: E.Okorie
Dam: Reynolds Lake Dam No. SURRY-031
Reservior Water
Level (RWS)
Elevation (ft)
Primary spillway
discharge (cfs)
Emergency spillway
discharge (cfs)
Total discharge from the
spillway system (cfs)
1477.5 0.0 0.0 0.0
1478.0 65.8 0.0 65.8
1478.5 186.0 0.0 186.0
1479.0 341.7 0.0 341.7
1479.5 526.1 0.0 526.1
1480.0 735.2 0.0 735.2
1480.5 966.5 0.0 966.5
1481.0 1217.9 0.0 1217.9
1481.5 1488.0 0.0 1488.0
1482.0 1775.5 0.0 1775.5
1482.5 2079.5 0.0 2079.5
1483.0 2399.1 0.0 2399.1
1483.5 2733.6 0.0 2733.6
1484.0 3082.4 0.0 3082.4
1484.5 3444.8 0.0 3444.8
1485.0 3820.4 0.0 3820.4
1485.5 4208.7 0.0 4208.7
1486.0 4609.4 0.0 4609.4
1486.5 5022.0 0.0 5022.0
1487.0 5446.3 0.0 5446.3
1487.5 5881.8 0.0 5881.8
1488.0 6328.4 0.0 6328.4
1488.5 6785.8 0.0 6785.8
1489.0 7253.7 0.0 7253.7
1489.5 7731.9 0.0 7731.9
1490.0 8220.1 0.0 8220.1
1490.5 8718.2 0.0 8718.2
1491.0 9226.0 0.0 9226.0
1491.5 9743.3 0.0 9743.3
1492.0 10269.9 0.0 10269.9
1492.5 10805.6 0.0 10805.6
1493.0 11350.4 0.0 11350.4
1493.5 11904.0 0.0 11904.0
1494.0 12466.3 0.0 12466.3
1494.5 13037.3 0.0 13037.3
1495.0 13616.6 0.0 13616.6
1495.5 14204.4 0.0 14204.4
1496.0 14800.3 0.0 14800.3
1496.5 15404.3 0.0 15404.3
1497.0 16016.4 0.0 16016.4
1497.5 16636.3 0.0 16636.3
1498.0 17264.1 0.0 17264.1
0.0
2000.0
4000.0
6000.0
8000.0
10000.0
12000.0
14000.0
16000.0
18000.0
20000.0
1475.0 1480.0 1485.0 1490.0 1495.0 1500.0Total discharge from the spillway system (cfs)Reservior Water Level (RWS) Elevation (ft)
The whole spillway system rating curve (cfs)