WAYNE-009_Final Report

DAM HYDRAULIC CAPACITY
ASSESSMENT REPORT

H. F. LEE STATION COOLING
LAKE DAM

WAYNE-009

WAYNE COUNTY, NC

PREPARED BY:
TYLER MCEWEN, PE
2020

EXECUTIVE SUMMARY
A hydraulic capacity analysis was completed for the H.F. Lee Station Cooling Lake Dam in Wayne
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 1.4 – 2.0 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 =
Concrete-Lined Broad-Crested Weir
Emergency Concrete-Lined Broad-Crested Weir
STORAGE (ACRE-FT)
5,328.6
641.5
ELEVATION
79.0
STORAGE (ACRE-FT)
2,956.1
3,548.9
NOT TO SCALE
87.0
4,735.386.0
79.0
80.0
81.0
82.0 2,364.3
1,781.0
4,141.985.0
1,206.9
84.0
0.0
118.1
SUMMARY SHEET OF HYDRAULIC CAPACITY RESULTS
H.F. Lee Station Cooling Lake Dam, WAYNE-009
SPILLWAY
ANALYSIS PERFORMED BY: TYLER MCEWEN, PE, NCDEQ-DEMLR
24 HOUR - 1000 YEAR EVENT, 15.40 INCHES, MAX W.S. ELEVATION 80.1 (1.4 FT FREEBOARD)
24 HOUR - 500 YEAR EVENT, 13.40 INCHES, MAX W.S. ELEVATION 79.9 (1.6 FT FREEBOARD)
24 HOUR - 200 YEAR EVENT, 11.10 INCHES, MAX W.S. ELEVATION 79.8 (1.7 FT FREEBOARD)
TOP OF DAM ELEVATION = 81.5 FT NAVD88
77.0
78.0
24 HOUR - 100 YEAR EVENT, 9.61 INCHES, MAX W.S. ELEVATION 79.7 (1.8 FT FREEBOARD)
ELEVATION (FT NAVD88)TYPE
80.5
Principal
ELEVATION
83.0
24 HOUR - 50 YEAR EVENT, 8.27 INCHES, MAX W.S. ELEVATION 79.6 (1.9 FT FREEBOARD)
24 HOUR - 25 YEAR EVENT, 7.07 INCHES, MAX W.S. ELEVATION 79.5 (2.0 FT FREEBOARD)
SUMMARY OF INPUT PARAMETERS
NRCS-NOAA
0.93
99
1
H.F. LEE PLANT COOLING LAKE DAM WAYNE-009 June 29, 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
H.F. Lee Cooling Lake Dam - WAYNE-009 Watershed Boundary
.Drainage Area: 0.93 Square Miles
Legend
Watershed Boundary
0 0.35 0.70.175 Miles

APPENDIX B 
Time of Concentration Calculation 

The StreamStats “longest flow path” for WAYNE-009 is completely contained within the cooling lake and
the time of concentration therefore assumed to be 1 minute for the HEC-HMS modeling.

APPENDIX C 
NRCS Curve Number Summary Sheet 

The entire watershed is composed of the cooling lake and is therefore open water. The curve number is
assumed to be 99.

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
18.0
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): Goldsboro, NC, USA
Station Name: -
Latitude: 35.3808°
Longitude: -78.0845°
Elevation (USGS): 59.6 ft
PRECIPITATION FREQUENCY ESTIMATES
by duration for
ARI (years):1 2 5 10 25 50 100 200 500 1000
5-min:0.443 0.517 0.591 0.665 0.745 0.81 0.871 0.929 1 1.06
10-min:0.707 0.826 0.946 1.06 1.19 1.29 1.38 1.47 1.58 1.68
15-min:0.884 1.04 1.2 1.35 1.51 1.63 1.75 1.86 1.99 2.1
30-min:1.21 1.44 1.7 1.95 2.23 2.46 2.68 2.89 3.17 3.41
60-min:1.51 1.8 2.18 2.54 2.97 3.33 3.69 4.06 4.55 4.97
2-hr:1.78 2.13 2.63 3.11 3.73 4.28 4.83 5.43 6.25 7
3-hr:1.89 2.27 2.81 3.36 4.07 4.72 5.39 6.12 7.17 8.14
6-hr:2.26 2.72 3.37 4.03 4.9 5.69 6.53 7.45 8.76 9.99
12-hr:2.66 3.19 3.97 4.78 5.84 6.84 7.89 9.06 10.8 12.4
24-hr:3.04 3.69 4.76 5.69 7.07 8.27 9.61 11.1 13.4 15.4
2-day:3.52 4.26 5.45 6.46 7.97 9.27 10.7 12.3 14.7 16.8
3-day:3.74 4.52 5.75 6.78 8.31 9.61 11 12.6 15 17
4-day:3.97 4.78 6.05 7.1 8.65 9.96 11.4 12.9 15.2 17.2
7-day:4.65 5.6 7.01 8.17 9.85 11.2 12.7 14.3 16.6 18.6
10-day:5.32 6.37 7.86 9.08 10.8 12.3 13.8 15.4 17.7 19.6
20-day:7.21 8.59 10.4 11.9 14 15.7 17.5 19.4 22 24.1
30-day:9 10.7 12.8 14.4 16.7 18.5 20.3 22.2 24.8 26.8
45-day:11.4 13.4 15.8 17.7 20.3 22.4 24.4 26.5 29.3 31.5
60-day:13.7 16.1 18.8 20.8 23.6 25.7 27.8 29.9 32.7 34.8
Date/time (GMT): Thu Jun 27 20:48:48 2019
pyRunTime: 0.0104458332062

APPENDIX F 
Outlet Works Rating Curves 

Primary Spillway:Rectangular Concrete Broad-crested Weir
Emergency Spillway:Rectangular Concrete Broad-crested Weir
Top of Dam :81.5 ft NAVD88
Normal Pool :79.0 ft NAVD88
RWS Elevation
(ft NAVD88)
Primary Spillway
Discharge (cfs)
Emergency Spillway
Discharge (cfs)
Total Structure
Discharge (cfs)
79.0 0 0 0
79.5 53 0 53
80.0 150 0 150
80.5 276 0 276
81.0 424 85 509
81.5 593 240 833
82.0 779 441 1,220
82.5 982 679 1,661
83.0 1,200 949 2,149
83.5 1,432 1,247 2,679
84.0 1,677 1,571 3,249
84.5 1,935 1,920 3,855
85.0 2,205 2,291 4,496
85.5 2,486 2,683 5,169
86.0 2,778 3,096 5,874
86.5 3,081 3,527 6,608
SPILLWAY ASSESSMENT
Crabtree Creek WS Dam #1 Dam, WAKE-127
79
80
81
82
83
84
85
86
87
0 1,000 2,000 3,000 4,000 5,000 6,000 7,000RWS Elevation (feet NAVD88)Spillway Discharge (cfs)
Spillway Discharge Capacity
Primary Spillway:Emergency Spillway:Total Structure