GRANV-005 Final Report

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A
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DAM HYDRAULIC CAPACITY
ASSESSMENT REPORT
NORWOOD DAM
G RANV-005
GRANVILLE COUNTY, NC
Rhonda��`'`,�`,"Q)�gitallysigned by
% a �L. Brewington
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PREPARED BY:
RHONDA L. BREWINGTON, PE
ALPHA Et OMEGA GROUP
2019
►,"
CA W-Aw
Founded 1998
ALPHA &OMEGA GROUP
CIVIL I STRUCTURAL j WATER RESOURCES

EXECUTIVE SUMMARY
A hydraulic capacity analysis was completed for the Norwood Dam in Granville County, North
Carolina. The purpose of the study was to analyze the existing potential of the dam 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 Arc-GIS 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 inadequate for all the
above rainfall events. The dam was overtopped during these events by 0.38 ft. to 0.59 ft. 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
NORWOOD DAM - GRANV-005
ANALYSIS PERFORMED BY: RHONDA L. BREWINGTON, PE (Alpha & Omega Group)
24 HOUR - 1000 YEAR EVENT, 9.82 INCHES, ELEVATION 354.13 (0.59 FT OVERTOPPED)
-----------------------------------------------
24 HOUR - 500 YEAR EVENT, 9.04 INCHES, ELEVATION 354.10 (0.56 FT OVERTOPPED)
-----------------------------------------------
24 HOUR - 200 YEAR EVENT, 8.05 INCHES, ELEVATION 354.05 (0.51 FT OVERTOPPED)
-----------------------------------------------
24 HOUR - 100 YEAR EVENT, 7.32 INCHES, ELEVATION 354.01 (0.47 FT OVERTOPPED)
-----------------------------------------------
24 HOUR - 50 YEAR EVENT, 6.60 INCHES, ELEVATION 353.97 (0.43 FT OVERTOPPED)
-----------------------------------------------
24 HOUR - 25 YEAR EVENT, 5.90 INCHES, ELEVATION 353.92 (0.38 FT OVERTOPPED)
SUMMARY OF INPUT PARAMETERS
Drainage Area (Sq. Mi.) = 0.21
Curve Number = 75.57
Lag Time (min.) = 23
Rainfall Distribution Methods = NRCS-NOAA
SPILLWAY
TYPE
ELEVATION
Principal
Riser / Barrel
351.27
Auxiliary
n/a
ELEVATION
STORAGE (ACRE -FT)
ELEVATION
STORAGE (ACRE -FT)
351.00
0.00
356.00
14.80
352.00
1.00
357.00
19.00
353.00
4.00
358.00
23.70
354.00
7.30
359.00
28.60
355.00
10.90
NOT TO SCALE
NORWOOD DAM GRANV-005 December 23, 2019

APPENDIX A
Watershed Boundary

Norwood Lake Dam - GRANV-005 - Watershed Boundary
N
Drainage Area: 0.21 Square Miles
Flowpath Length: 4,418.01 Feet w f E
5 Ii n
E J
0 0.05 0.1 0.2 Miles
I I I I I I I
GEBCO, USGS, FAO, NPS, NRCAN, GeoBase, IGN, Kadaster
NL, Ordnance Survey, Esri Japan, METI, Esri China (Hong Kong),
(c) OpenStreetMap contributors, and the GIS User Community

APPENDIX 6
Time of Concentration Calculation

Dam No: GRANV-005
Date: 12/16/2019
Dam Name: Norwood Dam
Engineer: R. Brewington
Input: R. Brewington
Checked: W. Needham
Maximum Potential Retention (inches): S =
(1000/cn')-10
Time of Concentration (hours):
Tc = I0.8*(S+1)0.7
1140*Y0-5
Basin Data:
Input Values in
yellow
Curve Number CN =
75.57
from StreamStats
S =
3.23276 in.
Mean Basin Slope Y =
9.54 %
from StreamStats
Longest Flowpath:
0.837 mi.
from StreamStats
Flow Length I =
4419.36 ft.
Time of Concentration
Tc = 0.64
Hours Tc =
39 mins
Lag Time
TL = 0.39
Hours TL =
23 mins

APPENDIX C
NRCS Curve Number Summary Sheet

Change CN according to TR-55 (see tables below)
HSG
Type
A
CN
B
CN
C
CN
D
CN
Open Water
0.0000
100
0
214.6421
100
21464.20653
939.3890
100
93938.8981
206011.7102
100
20601171
Developed, Open Space
0.0000
68
0
51004.4104
79
4029348.422
101341.3028
86
8715352.037
137219.9430
89
12212575
Developed, Low Intensity
0.0000
57
0
0.0000
72
0
26973.7439
81
2184873.254
8421.4074
86
724241
Developed, Medium Intensity
0.0000
77
0
0.0000
85
0
0.0000
90
0
0.0000
92
0
Developed, High Intensity
0.0000
89
0
0.0000
92
0
0.0000
94
0
0.0000
95
0
Barren Land
0.0000
77
0
0.0000
86
0
0.0000
91
0
0.0000
94
0
Deciduous Forest
0
36
0
526262.6882
60
31575761.29
677081.625
73
49426958.59
626830.9806
79
49519647
Evergreen Forest
0.0000
36
0
164424.1000
60
9865446.003
297929.4003
73
21748846.22
435463.0914
79
34401584
Mixed Forest
0.0000
36
0
50765.2868
60
3045917.207
0.0000
73
0
0.0000
79
0
Shrub/Scrub
0.0000
35
0
59169.4740
56
3313490.546
3597.8950
70
251852.6476
135087.2319
77
10401717
Herbaceuous
0.0000
50
0
712392.0744
71
50579837.28
430887.4997
81
34901887.47
131378.5250
89
11692689
Hay/Pasture
0
49
0
341202.2316
69
23542953.98
270087.665
79
21336925.57
160133.291
84
13451196
Cultivated Crops
0.0000
71
0
0.0000
80
0
160023.7738
87
13922068.32
22656.6009
90
2039094
Woody Wetlands
0.0000
80
0
0.0000
85
0
0.0000
90
0
0.0000
95
0
Emergent Herbaceuous Wetlands
0.0000
80
0
0.0000
85
0
0.0000
90
0
0.0000
95
0
NOTE: Curve Numbers are from SCS TR-55
with the exception
of assumed
HSG
A (CN=60) for
Herbaceous, Open Water, Woody
Wetlands,
and Emergent Herbaceous
Wetlands. Hydrologic Condition assumed as "Fair"
NOTE: double-check all the land types are
being calculated and texts are accurate
NOTE: double-check the exported attribute
table has the same table format as the "Export_Output" table
designed by dan.k

APPENDIX D
Hyetograph Results Used for Analyses

c
12.0
10.0
8.0
4.0
2.0
m
Hyetographs for 24-Hour Rainfall Distributions
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/hour)
NOAA Atlas 14 Volume 2 Version 3
Data type: Precipitation intensity
Time series type: Partial duration
Project area: Neuse River Basin
Location name (ESRI Maps): Stem North Carolina USA
Station Name: -
Latitude: 36.1867'
Longitude:-78.6961'
Elevation (USGS): 331.41 ft
PRECIPITATION FREQUENCY ESTIMATES
by duration for ARI
(years): 1 2 5 10 25 50 100 200 500 1000
5-min:
0.402
0.47
0.538
0.602
0.667
0.717
0.763
0.802
0.846
0.885
10-min:
0.642
0.751
0.861
0.962
1.06
1.14
1.21
1.27
1.34
1.39
15-min:
0.802
0.945
1.09
1.22
1.35
1.45
1.53
1.6
1.69
1.75
30-min:
1.1
1.31
1.55
1.76
2
2.18
2.35
2.5
2.68
2.83
60-min:
1.37
1.64
1.98
2.3
2.66
2.95
3.23
3.5
3.85
4.13
2-hr:
1.63
1.94
2.38
2.78
3.26
3.68
4.08
4.48
5.02
5.48
3-hr:
1.73
2.07
2.54
2.98
3.53
4
4.48
4.96
5.61
6.2
6-hr:
2.08
2.48
3.05
3.59
4.27
4.88
5.49
6.12
6.99
7.78
12-hr:
2.45
2.93
3.61
4.29
5.14
5.92
6.71
7.56
8.73
9.81
24-hr:
2.88
3.48
4.34
5
5.9
6.6
7.32
8.05
9.04
9.82
2-day:
3.38
4.07
5.02
5.75
6.71
7.46
8.22
8.99
10
10.8
3-day:
3.57
4.29
5.27
6.03
7.05
7.85
8.65
9.47
10.6
11.4
4-day:
3.76
4.51
5.53
6.32
7.39
8.23
9.09
9.96
11.1
12.1
7-day:
4.34
5.17
6.26
7.12
8.28
9.2
10.1
11.1
12.4
13.4
10-day:
4.92
5.85
7.01
7.93
9.16
10.1
11.1
12.1
13.4
14.5
20-day:
6.56
7.73
9.13
10.3
11.8
13
14.2
15.4
17.1
18.5
30-day:
8.13
9.57
11.1
12.3
13.9
15.1
16.3
17.5
19.1
20.4
45-day:
10.3
12.1
13.8
15.2
17
18.4
19.7
21.1
22.9
24.2
60-day:
12.4
14.5
16.3
17.7
19.6
20.9
22.3
23.5
25.2
26.4
Date/time (GMT):
Mon Dec 16 20:04:29 2019
pyRu nTi me: 0.0105571746826

APPENDIX F
Outlet Works Rating Curves

NORWOOD DAM
GRANV-005
Primary Spillway: 36" Double Wall HDPE Pipe
Auxiliary Spillway 1: N/A
SPILLWAY ASSESSMENT
RWS Elevation
(ft)
Primary Spillway
Discharge (cfs)
Auxiliary Spillway 1
Discharge (cfs)
Total Structure
Discharge (cfs)
351.3
0.0
0.0
0
351.6
1.3
0.0
1
351.9
3.7
0.0
4
352.2
6.9
0.0
7
352.5
10.6
0.0
11
352.8
14.8
0.0
15
353.1
19.4
0.0
19
353.4
24.5
0.0
24
353.7
29.9
0.0
30
354.0
35.6
0.0
36
354.3
41.7
0.0
42
354.6
45.7
0.0
46
354.9
49.3
0.0
49
355.2
52.7
0.0
53
355.5
55.9
0.0
56
355.8
59.0
0.0
59
356.1
61.8
0.0
62
356.4
64.6
0.0
65
356.7
67.2
0.0
67
357.0
69.8
0.0
70
357.3
72.2
0.0
72
357.6
74.6
0.0
75
357.9
76.9
0.0
77
358.2
79.1
0.0
79
358.5
81.3
0.0
81
358.8
83.4
0.0
83

RWS Elevation vs. Discharge Flow
360.0
359.0
358.0
357.0
356.0
0
v
w
355.0
354.0
353.0
352.0
351.0
0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0
Discharge Flow Rate (cfs)
Primary Spillway Auxiliary Spillway 1 — —Total Structure