PERSO-004 Final Report

DAM HYDRAULIC CAPACITY
ASSESSMENT REPORT
(DRAFT)
ROXBORO MUNICIPAL LAKE DAM
PERSO-004
PERSON COUNTY, NC
PREPARED BY:
WOOD E&I Solutions
2020

EXECUTIVE SUMMARY
A hydraulic capacity analysis was completed for the Roxboro Municipal Lake Dam
in Person 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 =
501.6
1712.5
1855.3
2000.9
492.1
492.6
493.1
493.6
494.1
498.1
498.6
499.1
500.1
496.6
497.1
497.6
500.6
501.1491.1
491.6
914.9
1041.2
1170.1
1301.5
1435.6
2300.6
2454.8
494.6
495.1
436.7
552.2
1572.6
2149.3
4163.2
487.1
487.6
488.1
488.6
489.1
3617.9
3796.6
3978.4
670.4
791.3
499.6
502.1
502.6
503.1
503.6
504.1
489.6
490.1
490.6
0.0
105.9
324.0
ELEVATION ELEVATION STORAGE (ACRE-FT)
Auxiliary Bridge crossing
486.6
490.4
495.6
496.1
SUMMARY SHEET OF HYDRAULIC CAPACITY RESULTS
ROXBORO MUNICIPAL LAKE DAM, PERSO-004
SPILLWAY
ANALYSIS PERFORMED BY: EKENE OKORIE, WOOD
24 HOUR - 1000 YEAR EVENT, 9.98 INCHES, ELEVATION 490.3 (0.1 FT FREEBOARD)
24 HOUR - 500 YEAR EVENT, 9.13 INCHES, ELEVATION 489.9 (0.5 FT FREEBOARD)
24 HOUR - 200 YEAR EVENT, 8.06 INCHES, ELEVATION 489.3 (1.1 FT FREEBOARD)
Principal
24 HOUR - 100 YEAR EVENT, 7.29 INCHES, ELEVATION 488.9 (1.5 FT FREEBOARD)
Rectangular Concrete chute 485.6
TOP OF DAM ELEVATION = 490.4
24 HOUR - 50 YEAR EVENT, 6.54 INCHES, ELEVATION 488.5 (2.0 FT FREEBOARD)
24 HOUR - 25 YEAR EVENT, 5.82 INCHES, ELEVATION 488.0 (2.4 FT FREEBOARD)
SUMMARY OF INPUT PARAMETERS
SCS Type 2
10.1079
71.54
145
ELEVATIONTYPE
504.6
505.0
2611.8
2771.7
2934.6
3100.6
STORAGE (ACRE-FT)
4351.1
4542.0
4736.1
4933.4
5133.9
5337.8
5544.9
5755.3
5969.1
6142.5
3269.7
3442.2
213.9
485.6
486.1
ROXBORO MUNICIPAL LAKE DAM PERSO-004 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 the
GIS User Community
Roxboro Municipal Lake Dam - PERSO-004 - Watershed Boundary
Legend
Longest FlowPath
Watershed Boundary
0 0.8 1.60.4 Miles
Date: 8/10/2020
/Drainage Area: 10.11 Square Miles
Flowpath Length: 6.41 Miles

APPENDIX B
Lag Time Calculation

Dam No: PERSO-004 Date: 7/14/2020
Dam Name: Roxboro Municipal Lake 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 = 71.54 from NRCS CN
S =3.97819 in.
Mean Basin Slope Y = 7.938 % from Watershed Mean slope
Longest Flowpath: 6.412 mi. from Watershed Longest flowpath
Flow Length l =33855.4 ft.
Time of Concentration Tc =4.03 Hours Tc =242 mins
Lag Time TL =2.42 Hours TL =145 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 547009 100 54700917 63654 100 6365398 10089913 100 1008991339 344801 100 34480133
Developed, Open Space Open space - Fair condition (grass cover 50% to 75%)489372 49 23979210 8224305 69 567477011 5498895 79 434412698 5133942 84 431251166
Developed, Low Intensity Residential districts by average lot size: 1/3 acre 41371 57 2358143 1995879 72 143703266 749764 81 60730898 1375444 86 118288197
Developed, Medium Intensity Residential districts by average lot size: 1/8 acre 0 77 0 257679 85 21902724 166535 90 14988113 158048 92 14540451
Developed, High Intensity Urban districts - Commercial and business 0 89 0 56342 92 5183478 11470 94 1078200 19375 95 1840621
Barren Land Newly graded areas 14105 77 1086119 0 86 0 14957 91 1361087 0 94 0
Deciduous Forest Woods - Fair 16446816 36 592085388 29202282 60 1752136933 55705648 73 4066512321 31113361 79 2457955491
Evergreen Forest Woods - Fair 1414280 36 50914071 3488291 60 209297435 3529059 73 257621331 1449794 79 114533701
Mixed Forest Woods - Fair 2428131 36 87412720 10184254 60 611055265 10865284 73 793165761 8320619 79 657328901
Shrub/Scrub Brush - Fair 736418 35 25774640 1369286 56 76679999 2382163 70 166751378 1439899 77 110872220
Herbaceuous Herbaceuous - Fair 964267 60 57855996 1747349 71 124061772 2166760 81 175507592 1042356 89 92769719
Hay/Pasture Pasture - Fair 514933 49 25231733 19017593 69 1312213912 12873905 79 1017038495 12717143 84 1068240030
Cultivated Crops Row crops (SR + CR) - Poor 54678 71 3882141 6771467 80 541717366 3908315 87 340023399 3555905 90 320031411
Woody Wetlands Not Available 174231 80 13938467 104270 85 8862916 89407 90 8046668 749422 95 71195090
Emergent Herbaceuous Wetlands Not Available 0 80 0 0 85 0 6263 90 563688 3424 95 325306 Weighted CN=71.54
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

0.02.04.06.08.010.012.00123456789101112131415161718192021222324Cumulative 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): Roxboro, North Carolina USA
Station Name: ‐
Latitude: 36.4055°
Longitude: ‐79.0269°
Elevation (USGS): None None
PRECIPITATION FREQUENCY ESTIMATES
by 
duration 
for ARI 
(years):1 2 5 10 25 50 100 200 500 1000
5‐min: 0.382 0.451 0.525 0.582 0.644 0.687 0.726 0.759 0.796 0.823
10‐min: 0.61 0.722 0.841 0.931 1.03 1.09 1.15 1.2 1.26 1.3
15‐min: 0.762 0.908 1.06 1.18 1.3 1.39 1.46 1.52 1.58 1.63
30‐min: 1.05 1.25 1.51 1.71 1.93 2.09 2.23 2.36 2.52 2.64
60‐min: 1.3 1.57 1.94 2.22 2.57 2.83 3.08 3.32 3.62 3.85
2‐hr: 1.55 1.87 2.31 2.68 3.14 3.5 3.86 4.22 4.69 5.06
3‐hr: 1.65 2 2.48 2.88 3.38 3.78 4.19 4.59 5.11 5.54
6‐hr: 2.01 2.42 3.01 3.5 4.15 4.69 5.24 5.8 6.58 7.21
12‐hr: 2.4 2.9 3.61 4.24 5.09 5.8 6.55 7.35 8.47 9.42
24‐hr: 2.81 3.39 4.24 4.9 5.81 6.54 7.29 8.06 9.13 9.98
2‐day: 3.31 3.99 4.93 5.66 6.64 7.41 8.2 9.01 10.1 11
3‐day: 3.49 4.2 5.18 5.94 6.98 7.8 8.63 9.49 10.7 11.6
4‐day: 3.67 4.41 5.43 6.23 7.32 8.18 9.07 9.98 11.2 12.2
7‐day: 4.22 5.03 6.12 6.98 8.15 9.09 10 11 12.4 13.4
10‐day: 4.79 5.69 6.85 7.77 9.01 9.99 11 12 13.4 14.5
20‐day: 6.4 7.56 8.96 10.1 11.6 12.8 14 15.3 17 18.3
30‐day: 7.94 9.34 10.9 12 13.6 14.8 16 17.2 18.7 19.9
45‐day: 10.1 11.8 13.5 14.9 16.7 18 19.4 20.7 22.4 23.7
60‐day: 12.1 14.1 15.9 17.3 19.2 20.5 21.8 23.1 24.6 25.8
Date/time (GMT):  Mon Jun 22 13:14:01 2020
pyRunTime:  0.0105819702148

APPENDIX F
Outlet Works Rating Curves

Total outlet discharge from the spillway system
Client: NCEM Date: 8/14/2020
Project: Overtopping Study Engineer: E.Okorie
Dam: Roxboro Municipal Lake Dam Dam No. PERSO-004
Reservior Water
Level (RWS)
Elevation (ft)
Primary spillway
discharge (cfs)
Emergency spillway
discharge (cfs)
Total discharge from the
spillway system (cfs)
485.6 0.0 0.0
486.1 186.3 0.0 186.3
486.6 527.0 0.0 527.0
487.1 968.2 0.0 968.2
487.6 1490.6 0.0 1490.6
488.1 2083.2 0.0 2083.2
488.6 2738.4 0.0 2738.4
489.1 3450.7 0.0 3450.7
489.6 4216.0 0.0 4216.0
490.1 5030.7 0.0 5030.7
490.6 5892.0 0.0 5892.0
491.1 6797.6 0.0 6797.6
491.6 7745.3 0.0 7745.3
492.1 8733.3 0.0 8733.3
492.6 9760.2 0.0 9760.2
493.1 10824.4 0.0 10824.4
493.6 11924.6 0.0 11924.6
494.1 13059.9 0.0 13059.9
494.6 14229.0 0.0 14229.0
495.1 15431.1 0.0 15431.1
495.6 16665.2 0.0 16665.2
496.1 17930.6 0.0 17930.6
496.6 19226.5 0.0 19226.5
497.1 20552.2 0.0 20552.2
497.6 21907.0 0.0 21907.0
498.1 23290.3 0.0 23290.3
498.6 24701.6 0.0 24701.6
499.1 26140.3 0.0 26140.3
499.6 27605.9 0.0 27605.9
500.1 29098.0 0.0 29098.0
500.6 30615.9 0.0 30615.9
501.1 32159.4 0.0 32159.4
501.6 33728.0 0.0 33728.0
502.1 35321.3 0.0 35321.3
502.6 36938.9 0.0 36938.9
503.1 38580.5 0.0 38580.5
503.6 40245.7 0.0 40245.7
504.1 41934.2 0.0 41934.2
504.6 43645.7 0.0 43645.7
505.1 45379.8 0.0 45379.8
505.6 47136.3 0.0 47136.3
506.1 48914.9 0.0 48914.9
506.6 50715.4 0.0 50715.4
507.1 52537.4 0.0 52537.4
507.6 54380.7 0.0 54380.7
0.0
10000.0
20000.0
30000.0
40000.0
50000.0
60000.0
480.0 485.0 490.0 495.0 500.0 505.0 510.0Total discharge from the spillway system (cfs)Reservior Water Level (RWS) Elevation (ft)
The whole spillway system rating curve (cfs)