PERSO-027 Final Report

DAM HYDRAULIC CAPACITY
ASSESSMENT REPORT
(DRAFT)
SOUTH HYCO LAKE DAM
PERSO-027
PERSON COUNTY, NC
PREPARED BY:
WOOD E&I Solutions
2020
EXECUTIVE SUMMARY
A hydraulic capacity analysis was completed for the South Hyco 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 =
501.9
3534.6
3816.7
4103.2
484.9
485.4
485.9
486.4
486.9
498.4
498.9
499.4
500.4
496.9
497.4
497.9
500.9
501.4483.9
484.4
1926.4
2184.4
2446.3
2712.2
2982.3
4688.7
4987.3
487.4
487.9
934.3
1176.5
3256.4
4394.0
13774.5
479.9
480.4
480.9
481.4
481.9
12580.7
12974.0
13371.9
1422.4
1672.4
499.9
502.4
502.9
503.4
503.9
504.4
482.4
482.9
483.4
0.0
230.4
696.3
ELEVATION ELEVATION STORAGE (ACRE‐FT)
Auxiliary Grass‐Lined  embankment
479.4
490.0
495.9
496.4
SUMMARY SHEET OF HYDRAULIC CAPACITY RESULTS
SOUTH HYCO LAKE DAM, PERSO‐027
SPILLWAY
ANALYSIS PERFORMED BY:  EKENE OKORIE, WOOD
24 HOUR ‐ 1000 YEAR EVENT, 9.82 INCHES, ELEVATION 484.8  (5.2 FT FREEBOARD)
24 HOUR ‐ 500 YEAR EVENT, 9.02 INCHES, ELEVATION 484.2  (5.8 FT FREEBOARD)
24 HOUR ‐ 200 YEAR EVENT, 8.01 INCHES, ELEVATION 483.5  (6.5 FT FREEBOARD)
Principal
24 HOUR ‐ 100 YEAR EVENT, 7.27 INCHES, ELEVATION 482.9 (7.1 FT FREEBOARD)
Rectangular Concrete chute 478.0
TOP OF DAM ELEVATION  = 490.0
24 HOUR ‐ 50 YEAR EVENT, 6.55 INCHES, ELEVATION 482.3  (7.7 FT FREEBOARD)
24 HOUR ‐ 25 YEAR EVENT, 5.84 INCHES, ELEVATION 481.7 (8.3 FT FREEBOARD)
SUMMARY OF INPUT PARAMETERS
SCS  Type 2
28.9491
72.48
230
ELEVATIONTYPE
504.9
505.4
10314.5
10681.2
11052.2
11427.7
STORAGE (ACRE‐FT)
488.4
488.9
14182.0
14594.5
15011.9
15434.1
15861.1
16292.7
16729.2
17170.5
17616.7
18067.9
11807.6
12191.9
462.1
478.0
478.9
489.4
489.9
490.4
490.9
491.4
491.9
5290.0
5596.9
5907.9
6223.1
6542.4
6865.8
7193.2
7524.4
505.9
506.4
506.9
507.4
507.9
508.4
508.9
18524.3
18986.0
19453.4
19926.5
20405.2
20889.5
21379.7
509.4 21875.7
492.9
492.4 7859.4
8198.4
493.4
509.9
510.4
510.9
22377.8
22886.0
23399.9
493.9
494.9
495.4
8541.2
8888.0
9238.7
9593.4
9951.9
511.4
511.9
512.4
23919.6
24444.9
24508.4
494.4
SOUTH HYCO LAKE DAM PERSO‐027 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
South Hyco Lake Dam - PERSO-027- Watershed Boundary
Legend
Longest FlowPath
Watershed Boundary
0 1.5 30.75 Miles
Date: 8/11/2020
/Drainage Area: 28.95 Square Miles
Flowpath Length: 12.01 Miles
APPENDIX B
Lag Time Calculation
Dam No: PERSO-027 Date: 7/16/2020
Dam Name: South Hyco 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 = 72.48 from NRCS CN
S =3.79691 in.
Mean Basin Slope Y = 8.148 % from Watershed Mean slope
Longest Flowpath: 12.0148 mi. from Watershed Longest flowpath
Flow Length l =63438.1 ft.
Time of Concentration Tc =6.40 Hours Tc =384 mins
Lag Time TL =3.84 Hours TL =230 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 912391 100 91239128 21207379 100 2120737924 854972 100 85497153 1222007 100 122200750
Developed, Open Space Open space - Fair condition (grass cover 50% to 75%)746315 49 36569426 7040459 69 485791667 9505451 79 750930643 12829089 84 1077643461
Developed, Low Intensity Residential districts by average lot size: 1/3 acre 83630 57 4766915 2468455 72 177728775 3558884 81 288269578 4645251 86 399491574
Developed, Medium Intensity Residential districts by average lot size: 1/8 acre 0 77 0 60208 85 5117681 149742 90 13476810 171145 92 15745369
Developed, High Intensity Urban districts - Commercial and business 0 89 0 0 92 0 9688 94 910682 0 95 0
Barren Land Newly graded areas 12607 77 970722 190132 86 16351326 27558 91 2507809 156265 94 14688892
Deciduous Forest Woods - Fair 35498458 36 1277944489 81796851 60 4907811073 63886591 73 4663721108 99368474 79 7850109463
Evergreen Forest Woods - Fair 10052297 36 361882694 13237457 60 794247415 24104439 73 1759624069 37588950 79 2969527021
Mixed Forest Woods - Fair 16357696 36 588877049 26651751 60 1599105054 34071115 73 2487191403 45667975 79 3607770056
Shrub/Scrub Brush - Fair 2917949 35 102128221 3404565 56 190655624 5831162 70 408181306 6371114 77 490575749
Herbaceuous Herbaceuous - Fair 2095199 60 125711956 3095941 71 219811784 6429596 81 520797292 10593611 89 942831405
Hay/Pasture Pasture - Fair 5577684 49 273306532 38894235 69 2683702202 51633494 79 4079046063 67574967 84 5676297269
Cultivated Crops Row crops (SR + CR) - Poor 789347 71 56043668 9706431 80 776514513 15973437 87 1389688999 21555289 90 1939976048
Woody Wetlands Not Available 0 80 0 48139 85 4091779 9688 90 871962 397520 95 37764395
Emergent Herbaceuous Wetlands Not Available 0 80 0 6183 85 525595 4586 90 412779 8607 95 817655 Weighted CN=72.48
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): Prospect Hill, North Carolina USA
Station Name: ‐
Latitude: 36.2788°
Longitude: ‐79.1568°
Elevation (USGS): None None
PRECIPITATION FREQUENCY ESTIMATES
by 
duration 
for ARI 
(years):1 2 5 10 25 50 100 200 500 1000
5‐min: 0.384 0.456 0.533 0.586 0.646 0.685 0.722 0.751 0.784 0.807
10‐min: 0.614 0.73 0.853 0.937 1.03 1.09 1.15 1.19 1.24 1.27
15‐min: 0.768 0.917 1.08 1.19 1.31 1.38 1.45 1.5 1.56 1.6
30‐min: 1.05 1.27 1.53 1.72 1.93 2.08 2.22 2.34 2.48 2.58
60‐min: 1.31 1.59 1.97 2.24 2.57 2.82 3.06 3.28 3.56 3.77
2‐hr: 1.56 1.89 2.35 2.7 3.15 3.5 3.84 4.18 4.63 4.97
3‐hr: 1.67 2.03 2.52 2.91 3.41 3.79 4.17 4.55 5.05 5.44
6‐hr: 2.03 2.46 3.06 3.54 4.19 4.7 5.23 5.77 6.51 7.1
12‐hr: 2.43 2.94 3.68 4.29 5.13 5.82 6.55 7.32 8.4 9.29
24‐hr: 2.85 3.44 4.28 4.94 5.84 6.55 7.27 8.01 9.02 9.82
2‐day: 3.35 4.03 4.97 5.7 6.66 7.41 8.17 8.95 9.99 10.8
3‐day: 3.54 4.25 5.23 5.99 7 7.8 8.61 9.44 10.6 11.4
4‐day: 3.72 4.46 5.48 6.28 7.35 8.19 9.06 9.93 11.1 12.1
7‐day: 4.27 5.1 6.18 7.04 8.19 9.11 10 11 12.3 13.3
10‐day: 4.85 5.76 6.92 7.83 9.06 10 11 12 13.4 14.4
20‐day: 6.48 7.64 9.04 10.2 11.7 12.9 14.1 15.4 17.1 18.4
30‐day: 8.04 9.46 11 12.2 13.7 14.9 16.1 17.3 18.9 20.1
45‐day: 10.2 11.9 13.7 15 16.8 18.2 19.5 20.9 22.7 24
60‐day: 12.3 14.3 16.1 17.5 19.3 20.7 22 23.2 24.8 26
Date/time (GMT):  Mon Jun 22 14:01:50 2020
pyRunTime:  0.0101091861725
APPENDIX F
Outlet Works Rating Curves
Total outlet discharge from the spillway system
Client:Date: 8/11/2020
Project:Engineer: E.Okorie
Dam:
NCEM
Overtopping Study
South Hyco Lake Dam No. PERSO-027
Reservior Water
Level (RWS)
Elevation (ft)
Primary spillway
discharge (cfs)
Emergency spillway
discharge (cfs)
Total discharge from the
spillway system (cfs)
478.0 0.0 0.0 0.0
478.5 219.2 0.0 219.2
479.0 620.0 0.0 620.0
479.5 1139.0 0.0 1139.0
480.0 1753.6 0.0 1753.6
480.5 2450.8 0.0 2450.8
481.0 3221.6 0.0 3221.6
481.5 4059.7 0.0 4059.7
482.0 4960.0 0.0 4960.0
482.5 5918.5 0.0 5918.5
483.0 6931.8 0.0 6931.8
483.5 7997.2 0.0 7997.2
484.0 9112.1 0.0 9112.1
484.5 10274.5 0.0 10274.5
485.0 11482.6 0.0 11482.6
485.5 12734.5 0.0 12734.5
486.0 14029.0 0.0 14029.0
486.5 15364.6 0.0 15364.6
487.0 16740.0 0.0 16740.0
487.5 18154.2 0.0 18154.2
488.0 19606.1 0.0 19606.1
488.5 21094.8 0.0 21094.8
489.0 22619.4 0.0 22619.4
489.5 24179.0 0.0 24179.0
490.0 25772.9 0.0 25772.9
490.5 27400.4 0.0 27400.4
491.0 29060.7 0.0 29060.7
491.5 30753.3 0.0 30753.3
492.0 32477.6 0.0 32477.6
492.5 34232.9 0.0 34232.9
493.0 36018.7 0.0 36018.7
493.5 37834.6 0.0 37834.6
494.0 39680.0 0.0 39680.0
494.5 41554.5 0.0 41554.5
495.0 43457.5 0.0 43457.5
495.5 45388.8 0.0 45388.8
496.0 47347.9 0.0 47347.9
496.5 49334.3 0.0 49334.3
497.0 51347.8 0.0 51347.8
497.5 53388.0 0.0 53388.0
498.0 55454.5 0.0 55454.5
498.5 57547.0 0.0 57547.0
499.0 59665.1 0.0 59665.1
499.5 61808.7 0.0 61808.7
500.0 63977.3 0.0 63977.3
500.5 66170.7 1.0 66171.7
0.0
10000.0
20000.0
30000.0
40000.0
50000.0
60000.0
70000.0
475.0 480.0 485.0 490.0 495.0 500.0 505.0Total discharge from the spillway system (cfs)Reservior Water Level (RWS) Elevation (ft)
The whole spillway system rating curve (cfs)