RANDO-185 Final Report

DAM HYDRAULIC CAPACITY
ASSESSMENT REPORT
(DRAFT)
ROBERT L. REECE LAKE DAM
RANDO-185
RANDOLPH COUNTY, NC
PREPARED BY:
HDR Engineering Inc. of the Carolinas
under contract with
WOOD E&I Solutions
2020

EXECUTIVE SUMMARY
A hydraulic capacity analysis was completed for the Robert L. Reece Lake Dam in Randolph
County, North Carolina. The purpose of the study was to analyze the existing potential of the dam
for overtopping during predetermined specified rainfall events using the North Carolina Dam
Safety defined process and templates. 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 =
Primary
Auxiliary
23786.0
19803.1
20445.2
21095.8
21755.1
22423.1
23100.0
461.8
462.3
462.8
463.3
463.8
ELEVATION
459.3
459.8
460.3
460.8
461.3
2839.1
STORAGE (ACRE-FT)
0.0
286.0
580.3
881.2
1189.1
1503.7
1826.6
443.3
440.3
440.8
441.3
441.8
442.3
442.8
438.8
NA
ELEVATION
438.8
439.3
439.8
STORAGE (ACRE-FT)
17929.2
18544.8
19169.6
2157.3
2494.6
SPILLWAY TYPE
Concrete Ogee
NA
ELEVATION
SUMMARY OF INPUT PARAMETERS
103.1
24 HOUR - 200 YEAR EVENT, 8.07 INCHES, ELEVATION 449 (4.8 FT FREE-BOARD)
24 HOUR - 100 YEAR EVENT, 7.32 INCHES, ELEVATION 448 (5.8 FT FREE-BOARD)
24 HOUR - 50 YEAR EVENT, 6.6 INCHES, ELEVATION 447 (6.8 FT FREE-BOARD)
24 HOUR - 25 YEAR EVENT, 5.89 INCHES, ELEVATION 446 (7.8 FT FREE-BOARD)
SUMMARY SHEET OF HYDRAULIC CAPACITY RESULTS
ROBERT L. REECE LAKE DAM, RANDO-185
ANALYSIS PERFORMED BY: S. MURPHY, HDR
74.42
376
SCS Type 2
TOP OF DAM ELEVATION = 453.8
24 HOUR - 1000 YEAR EVENT, 9.88 INCHES, ELEVATION 451.2 (2.6 FT FREE-BOARD)
24 HOUR - 500 YEAR EVENT, 9.08 INCHES, ELEVATION 450.2 (3.6 FT FREE-BOARD)
RANDO-185ROBERT L. REECE LAKE DAM OCTOBER 5, 2020
49317.8
NOT TO SCALE
43380.2
44339.5
45310.7
46293.9
47289.3
48297.2
37885.2
38771.4
39669.0
40578.2
41499.4
42433.3
32797.7
33618.8
34450.6
35292.9
36146.1
37010.2
28104.7
28859.8
29625.1
30400.9
31187.6
31987.0
24481.2
25186.0
25900.7
26625.4
27360.0
478.8
473.8
474.3
474.8
475.3
475.8
476.3
476.8
477.3
477.8
470.8
471.3
471.8
472.3
472.8
473.3
467.8
466.8
467.3
464.3
478.3
468.3
468.8
469.3
469.8
470.3
464.8
465.3
465.8
16140.3
16726.7
17323.1
12294.1
12816.6
13347.7
13887.2
14437.2
14995.9
9334.1
9807.3
10288.5
10777.7
11275.0
11780.4
6670.9
7094.0
466.3
8412.6
8869.1
4287.0
4666.5
5052.9
5446.6
5847.4
6255.5
15563.4
3190.7
3549.3
3914.7
458.3
458.8
455.3
455.8
456.3
456.8
457.3
457.8
452.3
452.8
7525.0
7964.5
453.3
453.8
454.3
454.8
449.3
449.8
450.3
450.8
451.3
451.8
446.3
446.8
447.3
447.8
448.3
448.8
443.8
444.3
444.8
445.3
445.8
RANDO-185ROBERT L. REECE LAKE DAM OCTOBER 5, 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
Robert L. Reece Lake Dam - RANDO-185 - Watershed Boundary
Legend
Longest FlowPath
Watershed Bound ary
0 3.5 71.75 Miles
Date: 10 /2/2020
/Drainage Ar ea: 103.1 Square MilesFlowpath Length: 27.5 miles

APPENDIX B

Lag Time Calculation
Dam No:RANDO-185 Date:10/8/2020
Dam Name:Robert L. Reece Lake Dam Engineer:K. Trefzger
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 =74.4239 from NRCS CN Calculation
S =3.43654 in.
Mean Basin Slope Y =10.2983 %from Watershed Mean slope
Longest Flowpath:27.51 mi.from Watershed Longest flowpath
Flow Length l =145253 ft.
Time of Concentration Tc =10.46 Hours Tc =627 mins
Lag Time TL =6.27 Hours TL =376 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 2974 100 297379 713145 100 71314495 2612013 100 261201340 29535539 100 #########
Developed, Open Space Open space - Fair condition (grass cover 50% to 75%)209774 49 10278934 81691074 69 5636684090 130481243 79 10308018202 58174209 84 #########
Developed, Low Intensity Residential districts by average lot size: 1/3 acre 21038 57 1199168 35932390 72 2587132047 53939021 81 4369060737 29615622 86 #########
Developed, Medium Intensity Residential districts by average lot size: 1/8 acre 0 77 0 5957255 85 506366672 12305371 90 1107483353 9085091 92 835828367
Developed, High Intensity Urban districts - Commercial and business 0 89 0 2031516 92 186899469 5271874 94 495556110 5054933 95 480218653
Barren Land Newly graded areas 0 77 0 212675 86 18290087 313583 91 28536036 626362 94 58877984
Deciduous Forest Woods - Fair 1420041 36 51121485 308645679 60 18518740750 707888538 73 51675863270 344190771 79 #########
Evergreen Forest Woods - Fair 2249 36 80961 27128391 60 1627703487 68129688 73 4973467246 41337793 79 #########
Mixed Forest Woods - Fair 121203 36 4363294 58203307 60 3492198432 144181330 73 10525237070 83376401 79 #########
Shrub/Scrub Brush - Fair 0 35 0 9311248 56 521429863 25895971 70 1812717940 14745742 77 #########
Herbaceuous Herbaceuous - Fair 0 60 0 11641158 71 826522212 22160444 81 1794995966 9809592 89 873053665
Hay/Pasture Pasture - Fair 304158 49 14903727 134021762 69 9247501597 208916708 79 16504419954 128586200 84 #########
Cultivated Crops Row crops (SR + CR) - Poor 84783 71 6019607 25337585 80 2027006833 23458553 87 2040894146 7039983 90 633598505
Woody Wetlands Not Available 0 80 0 1324469 85 112579838 1297384 90 116764540 1620557 95 153952905
Emergent Herbaceuous Wetlands Not Available 0 80 0 154466 85 13129593 187498 90 16874795 84211 95 8000056 Weighted CN=74.42
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 Analysis

0.0
2.0
4.0
6.0
8.0
10.0
12.0
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): Thomasville, North Carolina USA
Station Name: -
Latitude: 35.800689°
Longitude: -80.02113°
Elevation (USGS): 621.26 ft
PRECIPITATION FREQUENCY ESTIMATES
by
duration
for ARI
(years):1 2 5 10 25 50 100 200 500 1000
5-min:0.391 0.463 0.539 0.59 0.645 0.679 0.709 0.733 0.755 0.769
10-min:0.624 0.74 0.863 0.943 1.03 1.08 1.13 1.16 1.2 1.21
15-min:0.78 0.931 1.09 1.19 1.3 1.37 1.42 1.47 1.5 1.52
30-min:1.07 1.29 1.55 1.73 1.93 2.06 2.18 2.28 2.39 2.46
60-min:1.33 1.61 1.99 2.25 2.57 2.8 3 3.2 3.43 3.59
2-hr:1.57 1.9 2.36 2.69 3.12 3.43 3.73 4.02 4.38 4.65
3-hr:1.68 2.04 2.53 2.9 3.37 3.73 4.07 4.41 4.85 5.17
6-hr:2.04 2.46 3.06 3.52 4.13 4.6 5.07 5.54 6.17 6.65
12-hr:2.42 2.93 3.66 4.24 5.02 5.64 6.29 6.95 7.87 8.59
24-hr:2.87 3.46 4.32 4.99 5.89 6.6 7.32 8.07 9.08 9.88
2-day:3.34 4.02 4.98 5.71 6.69 7.45 8.22 9.01 10.1 10.9
3-day:3.54 4.25 5.25 6.01 7.04 7.85 8.67 9.51 10.6 11.5
4-day:3.74 4.49 5.51 6.31 7.39 8.24 9.11 10 11.2 12.2
7-day:4.28 5.1 6.19 7.05 8.21 9.13 10.1 11 12.3 13.4
10-day:4.87 5.79 6.95 7.85 9.07 10 11 12 13.3 14.4
20-day:6.54 7.72 9.11 10.2 11.7 12.9 14.1 15.4 17 18.4
30-day:8.09 9.51 11 12.2 13.8 15 16.2 17.4 19 20.2
45-day:10.2 11.9 13.6 15 16.7 18.1 19.4 20.7 22.4 23.7
60-day:12.2 14.2 16 17.4 19.2 20.6 21.9 23.1 24.8 26
Date/time (GMT): Thu Oct 8 21:02:56 2020
pyRunTime: 0.0157511234283

APPENDIX F
Outlet Works Rating Curves

Total outlet discharge from the spillway system
Client:NCEM Date:10/1/2020
Project:Overtopping Study Engineer:T.Carter
Dam:Robert L. Reece Lake Dam Dam No.RANDO-185
Reservior Water
Level (RWS)
Elevation (ft)
Primary spillway
discharge (cfs)
Total discharge from the
spillway system (cfs)
438.8 0.0 0.0
439.3 274.0 274.0
439.8 775.0 775.0
440.3 1423.8 1423.8
440.8 2192.0 2192.0
441.3 3063.5 3063.5
441.8 4027.0 4027.0
442.3 5074.6 5074.6
442.8 6200.0 6200.0
443.3 7398.1 7398.1
443.8 8664.8 8664.8
444.3 9996.4 9996.4
444.8 11390.1 11390.1
445.3 12843.2 12843.2
445.8 14353.2 14353.2
446.3 15918.2 15918.2
446.8 17536.2 17536.2
447.3 19205.7 19205.7
447.8 20925.0 20925.0
448.3 22692.7 22692.7
448.8 24507.7 24507.7
449.3 26368.5 26368.5
449.8 28274.2 28274.2
450.3 30223.8 30223.8
450.8 32216.1 32216.1
451.3 34250.5 34250.5
451.8 36325.9 36325.9
452.3 38441.7 38441.7
452.8 40597.0 40597.0
453.3 42791.1 42791.1
453.8 45023.4 45023.4
454.3 47293.3 47293.3
454.8 49600.0 49600.0
455.3 51943.1 51943.1
455.8 54321.9 54321.9
456.3 56736.0 56736.0
456.8 59184.8 59184.8
457.3 61667.9 61667.9
457.8 64184.8 64184.8
458.3 66735.0 66735.0
458.8 69318.1 69318.1
459.3 71933.7 71933.7
459.8 74581.4 74581.4
460.3 77260.8 77260.8
460.8 79971.6 79971.6
0.0
10000.0
20000.0
30000.0
40000.0
50000.0
60000.0
70000.0
80000.0
90000.0
435.0 440.0 445.0 450.0 455.0 460.0 465.0Total discharge from the spillway system (cfs)Reservior Water Level (RWS) Elevation (ft)
The whole spillway system rating curve (cfs)