WAYNE-031 Final Report

DAM HYDRAULIC CAPACITY
ASSESSMENT REPORT

H. F. LEE INACTIVE ASH POND DAM
#1

WAYNE-031

WAYNE COUNTY, NC

PREPARED BY:
TYLER MCEWEN, PE
2020

EXECUTIVE SUMMARY
A hydraulic capacity analysis was completed for the H.F. Lee Station Inactive Ash Pond Dam #1 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 not hydraulically adequate for
all of the above rainfall events. The dam is overtopped by 0.0 – 0.1 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
Emergency N/A
STORAGE (ACRE-FT)
164.6
1.1
ELEVATION
N/A
STORAGE (ACRE-FT)
62.3
87.8
NOT TO SCALE
85.0
139.084.0
77.0
78.0
79.0
80.0 37.9
17.7
113.483.0
5.3
82.0
0.0
0.5
SUMMARY SHEET OF HYDRAULIC CAPACITY RESULTS
H.F. Lee Inactive Ash Pond Dam #1, WAYNE-031
SPILLWAY
ANALYSIS PERFORMED BY: TYLER MCEWEN, PE, NCDEQ-DEMLR
24 HOUR - 1000 YEAR EVENT, 15.10 INCHES, MAX W.S. ELEVATION 78.8 (0.1 FT OVERTOPPING)
24 HOUR - 500 YEAR EVENT, 13.2 INCHES, MAX W.S. ELEVATION 78.8 (0.1 FT OVERTOPPING)
24 HOUR - 200 YEAR EVENT, 11.00 INCHES, MAX W.S. ELEVATION 78.8 (0.1 FT OVERTOPPING)
TOP OF DAM ELEVATION = 78.7 FT NAVD88
75.0
76.0
24 HOUR - 100 YEAR EVENT, 9.52 INCHES, MAX W.S. ELEVATION 78.7 (0.0 FT OVERTOPPING)
ELEVATION (FT NAVD88)TYPE
N/A
Principal
ELEVATION
81.0
24 HOUR - 50 YEAR EVENT, 8.21 INCHES, MAX W.S. ELEVATION 78.7 (0.0 FT OVERTOPPING)
24 HOUR - 25 YEAR EVENT, 7.03 INCHES, MAX W.S. ELEVATION 78.7 (0.0 FT OVERTOPPING)
SUMMARY OF INPUT PARAMETERS
NRCS-NOAA
0.045
99
1
H.F. LEE INACTIVE ASH POND DAM #1 WAYNE-031 June 30, 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 Inactive Ash Pond Dam #1 - WAYNE-031Watershed Boundary
.Drainage Area: 0.045 Square Miles
Legend
Watershed Boundary
0 0.15 0.30.075 Miles

APPENDIX B 
Time of Concentration Calculation 

The StreamStats did not produce a “longest flow path” for WAYNE-031. The lag time is assumed to be 1
minute for the HEC-HMS modeling.

APPENDIX C 
NRCS Curve Number Summary Sheet 

The entire watershed is composed of the inactive ash pond. 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
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: 35.3813°
Longitude: -78.1102°
Elevation (USGS): 71.96 ft
PRECIPITATION FREQUENCY ESTIMATES
by duration for
ARI (years):1 2 5 10 25 50 100 200 500 1000
5-min:0.441 0.515 0.589 0.663 0.742 0.807 0.867 0.925 0.994 1.06
10-min:0.704 0.824 0.943 1.06 1.18 1.28 1.38 1.47 1.57 1.67
15-min:0.88 1.04 1.19 1.34 1.5 1.63 1.74 1.85 1.98 2.09
30-min:1.21 1.43 1.69 1.94 2.22 2.45 2.67 2.88 3.15 3.39
60-min:1.51 1.8 2.17 2.53 2.96 3.32 3.67 4.04 4.52 4.95
2-hr:1.77 2.12 2.62 3.1 3.71 4.25 4.8 5.39 6.2 6.94
3-hr:1.88 2.26 2.8 3.34 4.04 4.69 5.35 6.08 7.11 8.07
6-hr:2.25 2.7 3.35 4.01 4.86 5.66 6.48 7.39 8.69 9.9
12-hr:2.64 3.17 3.95 4.75 5.81 6.79 7.83 8.99 10.7 12.2
24-hr:3.03 3.68 4.75 5.66 7.02 8.19 9.5 11 13.2 15.1
2-day:3.51 4.24 5.42 6.43 7.91 9.19 10.6 12.1 14.5 16.5
3-day:3.73 4.51 5.72 6.75 8.25 9.53 10.9 12.5 14.7 16.7
4-day:3.96 4.77 6.02 7.07 8.59 9.88 11.3 12.8 15 16.9
7-day:4.64 5.58 6.98 8.13 9.78 11.1 12.6 14.2 16.4 18.3
10-day:5.3 6.35 7.82 9.03 10.7 12.1 13.6 15.2 17.5 19.3
20-day:7.18 8.56 10.4 11.9 13.9 15.6 17.3 19.2 21.7 23.8
30-day:8.96 10.6 12.7 14.3 16.5 18.3 20.1 21.9 24.5 26.4
45-day:11.3 13.4 15.8 17.6 20.2 22.2 24.2 26.2 29 31.1
60-day:13.6 16 18.7 20.7 23.4 25.5 27.5 29.6 32.3 34.4
Date/time (GMT): Thu Jul 2 15:23:06 2020
pyRunTime: 0.0114109516144

APPENDIX F 
Outlet Works Rating Curves 

There is no free flow spillway for this inactive ash pond. The site is monitored due to the highly sensitive
nature of materials contained in the pond. The pond also faces external flood risks due to the ash
pond’s proximity to the Neuse River. There is no discharge rating curve for WAYNE-031.