WAYNE-028_Final Report

DAM HYDRAULIC CAPACITY
ASSESSMENT REPORT

DOUG JERNIGAN FARMS LAGOON
DIKE

WAYNE-028

WAYNE COUNTY, NC

PREPARED BY:
TYLER MCEWEN, PE
2020

EXECUTIVE SUMMARY
A hydraulic capacity analysis was completed for the Doug Jernigan Farms Lagoon 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 0.4 – 1.3 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 =
Principal
ELEVATION
140.0
141.0
0.0
0.1
N/A
SUMMARY SHEET OF HYDRAULIC CAPACITY RESULTS
DOUG JERNIGAN FARMS LAGOON DIKE, WAYNE-028
29.3
20.6
55.6142.0
145.0
12.2
SPILLWAY
ANALYSIS PERFORMED BY: TYLER MCEWEN, PE, NCDEQ-DEMLR
24 HOUR - 1000 YEAR EVENT, 15.70 INCHES, MAX W.S. ELEVATION 137.0 (0.4 FT FREEBOARD)
24 HOUR - 500 YEAR EVENT, 13.70 INCHES, MAX W.S. ELEVATION 136.8 (0.6 FT FREEBOARD)
24 HOUR - 200 YEAR EVENT, 11.30 INCHES, MAX W.S. ELEVATION 136.5 (0.9 FT FREEBOARD)
TOP OF DAM ELEVATION = 137.4 FT NAVD88
134.0
135.0
NOT TO SCALE
144.0
64.4143.0
136.0
137.0
138.0
139.0
24 HOUR - 100 YEAR EVENT, 9.78 INCHES, MAX W.S. ELEVATION 136.4 (1.0 FT FREEBOARD)
ELEVATION (FT NAVD88)TYPE
24 HOUR - 50 YEAR EVENT, 8.41 INCHES, MAX W.S. ELEVATION 136.3 (1.1 FT FREEBOARD)
24 HOUR - 25 YEAR EVENT, 7.18 INCHES, MAX W.S. ELEVATION 136.1 (1.3 FT FREEBOARD)
SUMMARY OF INPUT PARAMETERS
NRCS-NOAA
0.14
99
1
N/A
Auxiliary
STORAGE (ACRE-FT)
73.1
81.9
4.5
ELEVATION
N/A
STORAGE (ACRE-FT)
38.1
46.8
N/A
DOUG JERNIGAN FARMS LAGOON DIKE WAYNE-028 August 18, 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
Doug Jernigan Farms Lagoon Dike - WAYNE-028 Watershed Boundary
.Drainage Area: 0.014 Square Miles
Legend
Watershed Boundary
0 0.1 0.20.05 Miles

APPENDIX B 
Time of Concentration Calculation 

The StreamStats “longest flow path” for WAYNE-028 is completely contained within the Doug Jernigan
Farms lagoon. The time of concentration 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 Doug Jernigan Farms lagoon. 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): Mount Olive, NC, USA
Station Name: -
Latitude: 35.2331°
Longitude: -78.1209°
Elevation (USGS): 132.41 ft
PRECIPITATION FREQUENCY ESTIMATES
by duration for
ARI (years):1 2 5 10 25 50 100 200 500 1000
5-min:0.448 0.526 0.606 0.679 0.762 0.827 0.889 0.95 1.02 1.09
10-min:0.716 0.841 0.971 1.09 1.21 1.32 1.41 1.51 1.62 1.72
15-min:0.894 1.06 1.23 1.37 1.54 1.67 1.79 1.9 2.04 2.16
30-min:1.23 1.46 1.75 1.99 2.28 2.51 2.74 2.96 3.25 3.49
60-min:1.53 1.83 2.24 2.59 3.04 3.4 3.77 4.15 4.66 5.09
2-hr:1.8 2.17 2.7 3.18 3.82 4.38 4.96 5.58 6.46 7.24
3-hr:1.91 2.31 2.89 3.44 4.18 4.84 5.54 6.31 7.42 8.43
6-hr:2.29 2.76 3.46 4.12 5.03 5.84 6.71 7.67 9.07 10.3
12-hr:2.69 3.24 4.08 4.88 6 7.01 8.11 9.33 11.1 12.8
24-hr:3.07 3.73 4.82 5.76 7.18 8.41 9.78 11.3 13.7 15.7
2-day:3.57 4.32 5.53 6.56 8.11 9.44 10.9 12.6 15 17.1
3-day:3.79 4.58 5.83 6.89 8.45 9.79 11.3 12.9 15.3 17.4
4-day:4.02 4.85 6.13 7.21 8.8 10.1 11.6 13.2 15.6 17.6
7-day:4.71 5.67 7.11 8.3 10 11.4 13 14.6 17 18.9
10-day:5.38 6.45 7.96 9.2 11 12.4 14 15.7 18 20
20-day:7.3 8.69 10.6 12.1 14.2 16 17.8 19.7 22.4 24.6
30-day:9.11 10.8 12.9 14.6 16.9 18.8 20.6 22.6 25.2 27.3
45-day:11.5 13.6 16.1 18 20.6 22.7 24.8 27 29.9 32.2
60-day:13.8 16.3 19 21.1 23.9 26.1 28.2 30.4 33.2 35.4
Date/time (GMT): Mon Aug 17 21:06:39 2020
pyRunTime: 0.0110728740692

APPENDIX F 
Outlet Works Rating Curves 

WAYNE-028 Doug Jernigan Farms Lagoon Dike is a hog waste lagoon and designed as a temporary
storage facility. The waste is pumped out of the lagoon and sprayed on agricultural land as fertilizer.
For this simulation, the pump is assumed non-functioning during a flood emergency. Therefore, it is
assumed are no spillway discharges.