WAYNE-032 Final Report

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DAM HYDRAULIC CAPACITY
ASSESSMENT REPORT
H. F. LEE INACTIVE ASH POND DAM
#2
WAYN E-032
WAYNE COUNTY, NC
PREPARED BY:
TYLER MCEWEN, PE
2020

0
EXECUTIVE SUMMARY
A hydraulic capacity analysis was completed for the H.F. Lee Inactive Ash Pond Dam #2 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
the 100, 200, 500, and 1000 years return period 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).

SUMMARY SHEET OF HYDRAULIC CAPACITY RESULTS
H.F. Lee Inactive Ash Pond Dam #2, WAYNE-032
ANALYSIS PERFORMED BY: TYLER MCEWEN, PE, NCDEQ-DEMLR
24 HOUR - 1000 YEAR EVENT, 15.20 INCHES, MAX W.S. ELEVATION 78.8 (0.1 FT OVERTOPPING)
-------------------------------------------------
24 HOUR - 500 YEAR EVENT, 13.2 INCHES, MAX W.S. ELEVATION 78.7 (0.0 FT OVERTOPPING)
-------------------------------------------------
24 HOUR - 200 YEAR EVENT, 11.00 INCHES, MAX W.S. ELEVATION 78.7 (0.0 FT OVERTOPPING)
-------------------------------------------------
24 HOUR - 100 YEAR EVENT, 9.53 INCHES, MAX W.S. ELEVATION 78.7 (0.0 FT OVERTOPPING)
24 HOUR - 50 YEAR EVENT, 8.21 INCHES, MAX W.S. ELEVATION 78.6 (0.1 FT FREEBOARD)
-------------------------------------------------
24 HOUR - 25 YEAR EVENT, 7.03 INCHES, MAX W.S. ELEVATION 78.4 (0.3 FT FREEBOARD)
-------------------------------------------------
SUMMARY OF INPUT PARAMETERS
Drainage Area (Sq. Mi.) = 0.084
Curve Number = 99
Lag Time (min.) = 1
Rainfall Distribution Methods = NRCS-NOAA
SPILLWAY
TYPE
ELEVATION (FT NAVD88)
Principal
N/A
N/A
Emergency
N/A
N/A
ELEVATION
STORAGE (ACRE -FT)
ELEVATION
STORAGE (ACRE -FT)
75.0
0.0
81.0
136.7
76.0
5.6
82.0
189.2
77.0
10.6
83.0
242.3
78.0
22.4
84.0
295.5
79.0
48.0
85.0
348.7
80.0
88.1
NOT TO SCALE
H.F. LEE INACTIVE ASH POND DAM #2 WAYNE-032 July 1, 2020

APPENDIX A
Watershed Boundary

H.F. Lee Inactive Ash Pond Dam #2 - WAYNE-032

APPENDIX 6
Time of Concentration Calculation

The StreamStats did not produce a "longest flow path" for WAYNE-032. 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

Hyetographs for 24-Hour Rainfall Distributions
16.0
14.0
000,
12.0
a 10.0
0
V/00000
25YR
v
50YR
U
8.0
a,
100YR
r00,
f6
— 200YR
6.0
500YR
c.�
1000YR
4.0
2.0
0.0
0 2 4 6 8 10 12 14 16 18 20 22 24
Hours

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: 35.3828°
Longitude:-78.1041'
Elevation (USGS): 74.8 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
0.743
0.807
0.868
0.926
0.996
1.06
10-min:
0.705
0.824
0.943
1.06
1.18
1.29
1.38
1.47
1.58
1.67
15-min:
0.881
1.04
1.19
1.34
1.5
1.63
1.74
1.85
1.98
2.1
30-min:
1.21
1.43
1.7
1.95
2.22
2.45
2.67
2.88
3.16
3.39
60-min:
1.51
1.8
2.17
2.53
2.96
3.32
3.68
4.04
4.53
4.95
2-hr:
1.77
2.12
2.62
3.1
3.71
4.26
4.8
5.4
6.22
6.96
3-hr:
1.88
2.26
2.8
3.35
4.05
4.69
5.36
6.09
7.13
8.09
6-hr:
2.25
2.71
3.35
4.01
4.87
5.66
6.49
7.4
8.71
9.92
12-hr:
2.64
3.17
3.95
4.75
5.81
6.81
7.85
9.01
10.7
12.3
24-hr:
3.03
3.68
4.75
5.66
7.03
8.21
9.53
11
13.2
15.2
2-day:
3.51
4.25
5.43
6.44
7.93
9.21
10.6
12.2
14.5
16.5
3-day:
3.73
4.51
5.73
6.76
8.27
9.56
11
12.5
14.8
16.8
4-day:
3.96
4.77
6.03
7.08
8.61
9.9
11.3
12.8
15.1
17
7-day:
4.64
5.58
6.99
8.14
9.8
11.2
12.6
14.2
16.5
18.4
10-day:
5.31
6.36
7.83
9.04
10.8
12.2
13.7
15.3
17.5
19.4
20-day:
7.19
8.56
10.4
11.9
13.9
15.6
17.4
19.2
21.8
23.9
30-day:
8.97
10.6
12.7
14.3
16.6
18.3
20.2
22
24.5
26.5
45-day:
11.3
13.4
15.8
17.7
20.2
22.2
24.2
26.3
29.1
31.2
60-day:
13.6
16.1
18.7
20.7
23.5
25.5
27.6
29.7
32.4
34.5
Date/time (GMT): Thu Jul 2 15:24:23 2020
pyRunTime: 0.0112359523773

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-032.