WILSO-010_Final Report

DAM HYDRAULIC CAPACITY
ASSESSMENT REPORT

BUCKHORN LAKE DAM

WILSO-010

WILSON COUNTY, NC

PREPARED BY:
GEORGE ELLER, PE
2020

EXECUTIVE SUMMARY
A hydraulic capacity analysis was completed for the Buckhorn Lake Dam in Wislon County, North
Carolina. The purpose of the study was to analyze the existing potential of the dams 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 ArcGIS 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 all of the above rainfall events.
The dam maintained a freeboard of 9.2 – 13.1 feet during these 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. The
elevation-storage calculation does not include the storage below the normal pool elevation for
this study. All elevations in this report are based on North American Vertical Datum of 1988
(NAVD88).

Drainage Area (Sq. Mi.)=
Curve Number =
Lag Time (min.)=
Rainfall Distribution Methods =
N/A
Principal
ELEVATION
160.0
162.0
17,364.4
21,482.9
SUMMARY SHEET OF HYDRAULIC CAPACITY RESULTS
BUCKHORN LAKE DAM, WILSO-010
42,078.2
36,044.2
72,315.1164.0
170.0
30,280.7
SPILLWAY
ANALYSIS PERFORMED BY: GEORGE ELLER, PE, NCDEQ-DEMLR
24 HOUR - 1000 YEAR EVENT, 13.60 INCHES, MAX W.S. ELEVATION 154.2 (9.2 FT FREEBOARD)
24 HOUR - 500 YEAR EVENT, 12.00 INCHES, MAX W.S. ELEVATION 153.4 (10.0 FT FREEBOARD)
24 HOUR - 200 YEAR EVENT, 10.10 INCHES, MAX W.S. ELEVATION 152.3 (11.1 FT FREEBOARD)
TOP OF DAM ELEVATION = 163.4 FT NAVD88
146.0
148.0
NOT TO SCALE
168.0
81,964.5166.0
150.0
152.0
154.0
156.0
24 HOUR - 100 YEAR EVENT, 8.79 INCHES, MAX W.S. ELEVATION 151.6 (11.8 FT FREEBOARD)
ELEVATION (FT NAVD88)TYPE
24 HOUR - 50 YEAR EVENT, 7.64 INCHES, MAX W.S. ELEVATION 150.9 (12.5 FT FREEBOARD)
24 HOUR - 25 YEAR EVENT, 6.59 INCHES, MAX W.S. ELEVATION 150.3 (13.1 FT FREEBOARD)
SUMMARY OF INPUT PARAMETERS
NRCS-NOAA
159.0
70.75
703
158.0 48,701.5
Concrete-lined Ogee Spillway
Auxiliary N/A
STORAGE (ACRE-FT)
92,181.3
103,082.7
25,495.2
ELEVATION
147.0
STORAGE (ACRE-FT)
55,935.0
63,799.5
BUCKHORN LAKE DAM WILSO-010 June 19, 2020

APPENDIX A 
Watershed Boundary 

Sources: Esri, HERE, Garmin, Intermap, increment P Corp., GEBCO,USGS, FAO, NPS, NRCAN, GeoBase, IGN, Kadaster NL, OrdnanceSurvey, Esri Japan, METI, Esri China (Hong Kong), (c) OpenStreetMapcontributors, and the GIS User Community
Buckhorn Lake Dam - WILSO-010 Watershed Boundary
.Drainage Area: 159.0 Square MilesFlowpath Length: 160,174 Feet
Legend
Watershed Boundary
Longest Flowpath
0 3.5 71.75 Miles

APPENDIX B 
Time of Concentration Calculation 

Dam No:WILSO-010 Date:11/8/2018
Dam Name:Buckhorn Lake Dam Engineer:Y. Liu
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 =70.75 from StreamStats
S =4.13428 in.
Mean Basin Slope Y =4.24 %from StreamStats
Longest Flowpath:30.336 mi.from StreamStats
Flow Length l =160174 ft.
Time of Concentration Tc =19.52 Hours Tc =1171 mins
Lag Time TL =11.71 Hours TL =703 mins

APPENDIX C 
NRCS Curve Number Summary Sheet 

Change CN according to TR-55 (see tables below)
HSG
Type A CN B CN C CN D CN
Open Water 1930033.3894 100 193003338.9 19118665.6932 100 1911866569 7538154.9683 100 753815496.8 49805288.1071 100 4.98E+09
Developed, Open Space 53802089.2015 68 3658542066 148203523.8369 79 11708078383 25649116.5901 86 2205824027 42713010.9446 89 3.8E+09
Developed, Low Intensity 23398188.5878 57 1333696750 59933690.7744 72 4315225736 18977841.0225 81 1537205123 11533106.3037 86 9.92E+08
Developed, Medium Intensity 3645891.2546 77 280733626.6 5628868.1004 85 478453788.5 3242597.1375 90 291833742.4 1176198.8427 92 1.08E+08
Developed, High Intensity 1275934.1217 89 113558136.8 2196493.2703 92 202077380.9 757290.5398 94 71185310.75 506830.3571 95 48148884
Barren Land 1368453.9507 77 105370954.2 3346199.2973 86 287773139.6 315596.5196 91 28719283.29 225659.5043 94 21211993
Deciduous Forest 123661182.3 36 4451802564 557143943.7 60 33428636621 64509261.47 73 4709176087 280337492 79 2.21E+10
Evergreen Forest 70630833.0462 36 2542709990 346680664.5963 60 20800839876 42353996.0423 73 3091841711 175152982.6839 79 1.38E+10
Mixed Forest 13528299.8227 36 487018793.6 68657292.7305 60 4119437564 11210397.0086 73 818358981.6 55877973.3365 79 4.41E+09
Shrub/Scrub 14539865.2134 35 508895282.5 59999324.6357 56 3359962180 8176313.3581 70 572341935.1 41258968.2096 77 3.18E+09
Herbaceuous 25244318.3215 50 1262215916 74700732.7196 71 5303752023 13867246.5595 81 1123246971 48093881.5886 89 4.28E+09
Hay/Pasture 129861486.8 49 6363212855 341959617.1 69 23595213577 71740258.07 79 5667480388 49741461.35 84 4.18E+09
Cultivated Crops #############71 17893147916 420450853.1864 80 33636068255 65138275.6806 87 5667029984 75723441.1693 90 6.82E+09 designed by dan.k
Woody Wetlands 10999925.7278 80 879994058.2 58213766.2434 85 4948170131 9945117.2533 90 895060552.8 255162335.2437 95 2.42E+10
Emergent Herbaceuous Wetlands 637650.5243 80 51012041.94 1320246.9366 85 112220989.6 236140.1648 90 21252614.83 9576559.7665 95 9.1E+08 Weighted CN=70.75
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. Hydrologic Condition assumed as "Fair"
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 Analyses 

0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
0 2 4 6 8 10 12 14 16 18 20 22 24Cumulative Inches of RainHours
Hyetographs for 24-Hour 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): Kenly, NC, USA
Station Name: -
Latitude: 35.6919°
Longitude: -78.1178°
Elevation (USGS): 127.13 ft
PRECIPITATION FREQUENCY ESTIMATES
by duration for
ARI (years):1 2 5 10 25 50 100 200 500 1000
5-min:0.416 0.482 0.549 0.622 0.697 0.761 0.819 0.875 0.94 1
10-min:0.665 0.772 0.878 0.994 1.11 1.21 1.3 1.39 1.49 1.58
15-min:0.831 0.97 1.11 1.26 1.41 1.53 1.65 1.75 1.87 1.98
30-min:1.14 1.34 1.58 1.82 2.09 2.31 2.52 2.72 2.98 3.21
60-min:1.42 1.68 2.02 2.37 2.78 3.13 3.47 3.82 4.27 4.68
2-hr:1.66 1.97 2.41 2.88 3.45 3.97 4.49 5.05 5.82 6.53
3-hr:1.76 2.09 2.57 3.09 3.74 4.35 4.98 5.66 6.62 7.53
6-hr:2.1 2.5 3.07 3.7 4.49 5.25 6.02 6.87 8.08 9.23
12-hr:2.46 2.93 3.62 4.38 5.36 6.3 7.28 8.37 9.93 11.4
24-hr:2.91 3.53 4.52 5.36 6.59 7.64 8.79 10.1 12 13.6
2-day:3.36 4.07 5.17 6.09 7.44 8.58 9.83 11.2 13.2 14.9
3-day:3.58 4.32 5.46 6.4 7.78 8.93 10.2 11.5 13.6 15.2
4-day:3.79 4.57 5.74 6.71 8.11 9.28 10.5 11.9 13.9 15.6
7-day:4.42 5.3 6.6 7.66 9.16 10.4 11.7 13.1 15.1 16.8
10-day:5.05 6.03 7.4 8.5 10.1 11.3 12.7 14.1 16.1 17.7
20-day:6.79 8.06 9.72 11.1 12.9 14.4 16 17.6 19.9 21.7
30-day:8.43 9.97 11.8 13.3 15.3 16.9 18.5 20.1 22.4 24.1
45-day:10.7 12.6 14.7 16.4 18.6 20.4 22.2 24 26.4 28.2
60-day:12.8 15.1 17.4 19.2 21.6 23.5 25.3 27.1 29.5 31.3
Date/time (GMT): Tue Nov 13 14:40:10 2018
pyRunTime: 0.0111758708954

APPENDIX F 
Outlet Works Rating Curves 

Primary Spillway:Concrete-lined Ogee Spillway
Emergency Spillway:N/A
Top of Dam :163.4 ft NAVD88
Normal Pool :146.9 ft NAVD88
RWS Elevation
(ft NAVD88)
Primary Spillway
Discharge (cfs)
Emergency Spillway
Discharge (cfs)
Total Structure
Discharge (cfs)
146.5 0 0 0
147.0 9 0 9
147.5 544 0 544
148.0 1,529 0 1,529
148.5 2,821 0 2,821
149.0 4,472 0 4,472
149.5 6,341 0 6,341
150.0 8,477 0 8,477
150.5 10,870 0 10,870
151.0 13,464 0 13,464
151.5 16,290 0 16,290
152.0 19,310 0 19,310
152.5 22,547 0 22,547
153.0 26,100 0 26,100
153.5 29,616 0 29,616
154.0 33,062 0 33,062
154.5 36,631 0 36,631
155.0 40,317 0 40,317
155.5 44,116 0 44,116
156.0 48,025 0 48,025
156.5 52,041 0 52,041
157.0 56,160 0 56,160
157.5 60,380 0 60,380
158.0 64,697 0 64,697
158.5 69,110 0 69,110
159.0 73,616 0 73,616
159.5 78,213 0 78,213
160.0 82,899 0 82,899
160.5 87,672 0 87,672
161.0 92,529 0 92,529
161.5 97,471 0 97,471
162.0 102,493 0 102,493
162.5 107,596 0 107,596
163.0 112,778 0 112,778
163.5 118,036 0 118,036
164.0 123,371 0 123,371
164.5 128,780 0 128,780
165.0 134,262 0 134,262
165.5 139,816 0 139,816
166.0 145,442 0 145,442
166.5 151,136 0 151,136
167.0 156,900 0 156,900
167.5 162,731 0 162,731
168.0 168,629 0 168,629
168.5 174,592 0 174,592
169.0 180,621 0 180,621
169.5 186,713 0 186,713
170.0 192,867 0 192,867
SPILLWAY ASSESSMENT
Buckhorn Lake Dam, WILSO-010
146
148
150
152
154
156
158
160
162
164
166
168
170
172
0 20,000 40,000 60,000 80,000 100,000 120,000 140,000 160,000 180,000 200,000RWS Elevation (feet NAVD88)Spillway Discharge (cfs)
Spillway Discharge Capacity
Primary Spillway:Emergency Spillway:Total Structure