WAYNE-022 Final Report

DAM HYDRAULIC CAPACITY
ASSESSMENT REPORT

H. F. LEE ACTIVE ASH POND

WAYNE-022

WAYNE COUNTY, NC

PREPARED BY:
TYLER MCEWEN, PE
2020

EXECUTIVE SUMMARY
A hydraulic capacity analysis was completed for the H.F. Lee Active Ash Pond 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 2.1 – 4.0 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 =
N/A
Principal
ELEVATION
87.0
88.0
4.6
5.8
SUMMARY SHEET OF HYDRAULIC CAPACITY RESULTS
H.F. LEE ACTIVE ASH POND DAM, WAYNE-022
22.0
10.0
221.089.0
92.0
8.6
SPILLWAY
ANALYSIS PERFORMED BY: GEORGE ELLER, PE, NCDEQ-DEMLR
24 HOUR - 1000 YEAR EVENT, 15.50 INCHES, MAX W.S. ELEVATION 86.2 (2.1 FT FREEBOARD)
24 HOUR - 500 YEAR EVENT, 13.50 INCHES, MAX W.S. ELEVATION 85.8 (2.5 FT FREEBOARD)
24 HOUR - 200 YEAR EVENT, 11.20 INCHES, MAX W.S. ELEVATION 85.3 (3.0 FT FREEBOARD)
TOP OF DAM ELEVATION = 88.3 FT NAVD88
78.0
79.0
NOT TO SCALE
91.0
284.290.0
80.0
81.0
82.0
83.0
85.0 61.1 94.0 616.1
86.0 87.0
24 HOUR - 100 YEAR EVENT, 9.67 INCHES, MAX W.S. ELEVATION 85.0 (3.3 FT FREEBOARD)
ELEVATION (FT NAVD88)TYPE
24 HOUR - 50 YEAR EVENT, 8.31 INCHES, MAX W.S. ELEVATION 84.6 (3.7 FT FREEBOARD)
24 HOUR - 25 YEAR EVENT, 7.09 INCHES, MAX W.S. ELEVATION 84.3 (4.0 FT FREEBOARD)
SUMMARY OF INPUT PARAMETERS
NRCS-NOAA
0.18
99
1
521.293.084.0 40.4
15-inch RCP Barrel
Auxiliary N/A
STORAGE (ACRE-FT)
356.2
434.9
7.2
ELEVATION
81.0
STORAGE (ACRE-FT)
121.6
166.5
H.F. LEE ACTIVE ASH POND DAM WAYNE-022 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 Active Ash Pond Dam - WAYNE-022 Watershed Boundary
.Drainage Area: 0.18 Square Miles
Legend
Watershed Boundary
0 0.5 10.25 Miles

APPENDIX B 
Time of Concentration Calculation 

The StreamStats “longest flow path” for WAYNE-022 is completely contained within the active ash pond
and is 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 active ash pond 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: 35.3791°
Longitude: -78.0698°
Elevation (USGS): 83.48 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 0.592 0.666 0.746 0.811 0.872 0.931 1 1.07
10-min:0.708 0.828 0.947 1.07 1.19 1.29 1.39 1.48 1.59 1.68
15-min:0.885 1.04 1.2 1.35 1.51 1.64 1.75 1.86 2 2.11
30-min:1.21 1.44 1.7 1.95 2.23 2.46 2.68 2.9 3.18 3.42
60-min:1.51 1.8 2.18 2.54 2.97 3.34 3.7 4.07 4.56 4.99
2-hr:1.78 2.13 2.63 3.12 3.73 4.29 4.84 5.44 6.27 7.03
3-hr:1.89 2.27 2.82 3.37 4.08 4.73 5.4 6.14 7.2 8.17
6-hr:2.27 2.72 3.38 4.04 4.91 5.71 6.55 7.47 8.8 10
12-hr:2.66 3.19 3.98 4.79 5.86 6.86 7.92 9.1 10.8 12.4
24-hr:3.04 3.69 4.77 5.7 7.09 8.31 9.67 11.2 13.5 15.5
2-day:3.52 4.26 5.45 6.48 8 9.31 10.8 12.4 14.8 16.9
3-day:3.75 4.53 5.76 6.8 8.34 9.66 11.1 12.7 15.1 17.1
4-day:3.97 4.79 6.06 7.12 8.68 10 11.4 13 15.3 17.3
7-day:4.66 5.61 7.03 8.2 9.89 11.3 12.8 14.4 16.8 18.7
10-day:5.33 6.38 7.88 9.11 10.9 12.3 13.8 15.5 17.9 19.8
20-day:7.23 8.61 10.5 12 14.1 15.8 17.6 19.5 22.2 24.3
30-day:9.01 10.7 12.8 14.5 16.7 18.5 20.4 22.3 24.9 27
45-day:11.4 13.5 15.9 17.8 20.4 22.5 24.6 26.7 29.6 31.8
60-day:13.7 16.1 18.8 20.9 23.7 25.8 27.9 30.1 32.9 35
Date/time (GMT): Tue Apr 17 17:30:53 2018
pyRunTime: 0.0214490890503

APPENDIX F 
Outlet Works Rating Curves 

Primary Spillway:37.5-inch Inside Diameter RCP
Emergency Spillway:N/A
Top of Dam :88.3 ft NAVD88
Normal Pool :81.0 ft NAVD88
RWS Elevation
(ft NAVD88)
Primary Spillway
Discharge (cfs)
Emergency Spillway
Discharge (cfs)
Total Structure
Discharge (cfs)
81.0 0 0 0
81.5 2 0 2
82.0 8 0 8
82.5 15 0 15
83.0 22 0 22
83.5 30 0 30
84.0 40 0 40
84.5 50 0 50
85.0 57 0 57
85.5 65 0 65
86.0 70 0 70
86.5 75 0 75
87.0 78 0 78
87.5 84 0 84
88.0 87 0 87
88.5 91 0 91
89.0 95 0 95
89.5 98 0 98
90.0 100 0 100
SPILLWAY ASSESSMENT
H.F. Lee Active Ash Pond Dam, WAYNE-022
80
81
82
83
84
85
86
87
88
89
90
91
0 10 20 30 40 50 60 70 80 90 100 110RWS Elevation (feet NAVD88)Spillway Discharge (cfs)
Spillway Discharge Capacity
Primary Spillway:Emergency Spillway:Total Structure