WAKE-081 Final Report

DAM HYDRAULIC CAPACITY
ASSESSMENT REPORT

BEAVERDAM CREEK LAKE DAM

WAKE-081

WAKE COUNTY, NC

PREPARED BY:
GEORGE ELLER, PE
2020

EXECUTIVE SUMMARY
A hydraulic capacity analysis was completed for the Beaverdam Creek Lake Dam in Wake 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 2.9 – 7.0 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 =
11,495.3263.0254.0 2,999.8
Concrete-lined Rectangular Channel/Weir
Auxiliary N/A
STORAGE (ACRE-FT)
9,458.5
10,465.6
24.5
ELEVATION
255.8
STORAGE (ACRE-FT)
5,644.6
6,566.1
24 HOUR - 100 YEAR EVENT, 7.36 INCHES, MAX W.S. ELEVATION 253.7 (5.5 FT FREEBOARD)
ELEVATION (FT NAVD88)TYPE
24 HOUR - 50 YEAR EVENT, 6.63 INCHES, MAX W.S. ELEVATION 253.0 (6.2 FT FREEBOARD)
24 HOUR - 25 YEAR EVENT, 5.92 INCHES, MAX W.S. ELEVATION 252.2 (7.0 FT FREEBOARD)
SUMMARY OF INPUT PARAMETERS
NRCS-NOAA
52.4
77.75
246
NOT TO SCALE
261.0
8,472.9260.0
250.0
251.0
252.0
253.0
255.0 3,862.0 264.0 12,548.7
256.0 4,743.4 265.0 13,627.6
SUMMARY SHEET OF HYDRAULIC CAPACITY RESULTS
BEAVERDAM CREEK LAKE DAM, WAKE-081
2,156.5
1,334.7
7,508.7259.0
262.0
537.3
SPILLWAY
ANALYSIS PERFORMED BY: GEORGE ELLER, PE, NCDEQ-DEMLR
24 HOUR - 1000 YEAR EVENT, 9.92 INCHES, MAX W.S. ELEVATION 256.3 (2.9 FT FREEBOARD)
24 HOUR - 500 YEAR EVENT, 9.12 INCHES, MAX W.S. ELEVATION 255.5 (3.7 FT FREEBOARD)
24 HOUR - 200 YEAR EVENT, 8.11 INCHES, MAX W.S. ELEVATION 254.5 (4.7 FT FREEBOARD)
TOP OF DAM ELEVATION = 259.2 FT NAVD88
248.0
249.0
N/A
Principal
ELEVATION
257.0
258.0
0.0
4.9
BEAVERDAM CREEK DAM WAKE-081 June 13, 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
Beaverdam Creek Lake Dam - WAKE-081 - Watershed Boundary
.Drainage Area: 52.4 Square MilesFlowpath Length: 75,525 Feet
Legend
Watershed Boundary
Longest Flowpath
0 2.5 51.25 Miles

APPENDIX B 
Time of Concentration Calculation 

Dam No:Wake-081 Date:8/22/2018
Dam Name:Beaver Creek Dam Engineer:G. Eller (Designer)
Modeler:Sue White
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 =77.75 from StreamStats
S =2.86174 in.
Mean Basin Slope Y =6.99 %from StreamStats
Longest Flowpath:14.304 mi.from StreamStats
Flow Length l =75525.1 ft.
Time of Concentration Tc =6.82 Hours Tc =409 mins
Lag Time TL =4.09 Hours TL =246 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 2529.9590 100 252995.8954 73625466.1197 100 7362546612 59546.1464 100 5954614.641 8097556.8010 100 8.1E+08
Developed, Open Space 7067420.1244 68 480584568.5 11935347.0584 79 942892417.6 2697452.2864 86 231980896.6 44194867.7370 89 3.93E+09
Developed, Low Intensity 1243447.4821 57 70876506.48 2100636.4650 72 151245825.5 169294.1460 81 13712825.83 12924833.1208 86 1.11E+09
Developed, Medium Intensity 206190.8188 77 15876693.05 178237.2723 85 15150168.15 68736.5944 90 6186293.497 1968370.8054 92 1.81E+08
Developed, High Intensity 246.9544 89 21978.94299 44882.6018 92 4129199.368 0.0000 94 0 324168.2643 95 30795985
Barren Land 0.0000 77 0 181042.7696 86 15569678.19 0.0000 91 0 1048974.2002 94 98603575
Deciduous Forest 17442561.95 36 627932230.3 99413547.04 60 5964812823 14034830.49 73 1024542626 262181192.7 79 2.07E+10
Evergreen Forest 17604401.5138 36 633758454.5 67573682.8351 60 4054420970 20362871.4492 73 1486489616 260774226.1060 79 2.06E+10
Mixed Forest 6072652.8255 36 218615501.7 25826402.7908 60 1549584167 5392586.4843 73 393658813.4 81947811.1519 79 6.47E+09
Shrub/Scrub 1010582.8031 35 35370398.11 6677337.0059 56 373930872.3 1746571.1955 70 122259983.7 46028481.5080 77 3.54E+09
Herbaceuous 5683348.2742 50 284167413.7 15404556.2334 71 1093723493 1410012.9727 81 114211050.8 78640956.1906 89 7E+09
Hay/Pasture 7427362.324 49 363940753.9 23214223.82 69 1601781443 3531200.69 79 278964854.5 139010850.7 84 1.17E+10
Cultivated Crops 0.0000 71 0 973501.5314 80 77880122.51 0.0000 87 0 20729257.3720 90 1.87E+09 designed by dan.k
Woody Wetlands 0.0000 80 0 1957745.7176 85 166408386 495995.5023 90 44639595.21 59152730.9506 95 5.62E+09
Emergent Herbaceuous Wetlands 0.0000 80 0 7310.8409 85 621421.4759 19188.6530 90 1726978.768 1218317.2086 95 1.16E+08 Weighted CN=77.75
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
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): Wake Forest, North Carolina, USA
Station Name: -
Latitude: 36.0250°
Longitude: -78.6880°
Elevation (USGS): 244.9 ft
PRECIPITATION FREQUENCY ESTIMATES
by duration
for ARI
(years):1 2 5 10 25 50 100 200 500 1000
5-min:0.404 0.471 0.539 0.601 0.665 0.712 0.755 0.792 0.833 0.867
10-min:0.645 0.753 0.863 0.962 1.06 1.14 1.2 1.26 1.32 1.37
15-min:0.806 0.947 1.09 1.22 1.34 1.44 1.52 1.58 1.66 1.71
30-min:1.11 1.31 1.55 1.76 1.99 2.16 2.32 2.47 2.64 2.78
60-min:1.38 1.64 1.99 2.3 2.65 2.93 3.2 3.46 3.79 4.05
2-hr:1.62 1.93 2.37 2.75 3.22 3.61 3.99 4.37 4.86 5.28
3-hr:1.72 2.06 2.52 2.96 3.49 3.95 4.4 4.87 5.49 6.04
6-hr:2.07 2.47 3.04 3.56 4.22 4.8 5.38 5.98 6.79 7.51
12-hr:2.44 2.92 3.6 4.25 5.08 5.82 6.56 7.36 8.45 9.43
24-hr:2.88 3.48 4.34 5.01 5.92 6.63 7.36 8.11 9.12 9.92
2-day:3.36 4.04 5 5.74 6.73 7.5 8.28 9.08 10.2 11
3-day:3.55 4.26 5.26 6.03 7.06 7.88 8.7 9.55 10.7 11.6
4-day:3.75 4.49 5.51 6.32 7.4 8.26 9.13 10 11.2 12.2
7-day:4.33 5.16 6.26 7.13 8.31 9.24 10.2 11.2 12.5 13.5
10-day:4.92 5.84 7.01 7.92 9.16 10.1 11.1 12.1 13.4 14.5
20-day:6.57 7.74 9.14 10.3 11.8 13 14.2 15.4 17.1 18.4
30-day:8.15 9.59 11.1 12.3 13.9 15.1 16.3 17.6 19.2 20.4
45-day:10.4 12.1 13.9 15.3 17 18.4 19.7 21 22.8 24.1
60-day:12.5 14.5 16.4 17.8 19.6 21 22.4 23.7 25.3 26.6
Date/time (GMT): Mon Apr 16 14:33:03 2018
pyRunTime: 0.0398609638214

APPENDIX F 
Outlet Works Rating Curves 

Primary Spillway:Concrete-Lined Rectangular Channel/Weir
Emergency Spillway:N/A
Top of Dam :259.2 ft NAVD88
Normal Pool :245.2 ft NAVD88
RWS Elevation
(ft NAVD88)
Primary Spillway
Discharge (cfs)
Emergency Spillway
Discharge (cfs)
Total Structure
Discharge (cfs)
245.2 0 0 0
245.7 212 0 212
246.2 600 0 600
246.7 1,102 0 1,102
247.2 1,697 0 1,697
247.7 2,372 0 2,372
248.2 3,118 0 3,118
248.7 3,929 0 3,929
249.2 4,800 0 4,800
249.7 5,728 0 5,728
250.2 6,708 0 6,708
250.7 7,739 0 7,739
251.2 8,818 0 8,818
251.7 9,943 0 9,943
252.2 11,112 0 11,112
252.7 12,324 0 12,324
253.2 13,576 0 13,576
253.7 14,869 0 14,869
254.2 16,200 0 16,200
254.7 17,569 0 17,569
255.2 18,974 0 18,974
255.7 20,414 0 20,414
256.2 21,890 0 21,890
256.7 23,399 0 23,399
257.2 24,942 0 24,942
257.7 26,517 0 26,517
258.2 28,123 0 28,123
258.7 29,761 0 29,761
259.2 31,430 0 31,430
259.7 33,341 0 33,341
260.2 35457 1 35,458
260.7 37716 2 37,718
261.2 40097 3 40,100
261.7 42586 4 42,590
262.2 45173 5 45,178
262.7 47853 6 47,859
263.2 50621 7 50,628
263.7 53470 8 53,478
264.2 56400 9 56,409
264.7 59405 10 59,415
SPILLWAY ASSESSMENT
Beaverdam Creek Lake Dam, WAKE-081
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
0 10,000 20,000 30,000 40,000 50,000 60,000RWS Elevation (feet NAVD88)Spillway Discharge (cfs)
Spillway Discharge Capacity
Primary Spillway:Emergency Spillway:Total Structure