SW3240204_Design Calculations_20240617

Appendix C
Supporting Calculations
NOAA Atlas 14 Precipitation Data
Time of Concentration
Diversion Swale for Post Construction
USGS StreamStats Peak Flow
Culvert Calculations
Riprap Outlet Protection Calculations

NOAA Atlas 14 Precipitation Data

NOAA Atlas 14,Volume 2,Version 3
,ff"e°```"v,, Location name: Fairview,North Carolina, USA* ',,,u''I
Latitude:35.1305°,Longitude: -80.4945° ii
nnFin
%? Iii Elevation: 514 ft** i
�s.r U.+ w*source:ESRI Maps " "'
`a°` **source:USGS x""`" `'
POINT PRECIPITATION FREQUENCY ESTIMATES
G.M.Bonnin,D.Martin,B.Lin,T.Parzybok,M.Yekta,and D.Riley
NOAA,National Weather Service,Silver Spring,Maryland
PF tabular I PF graphical I Maps & aerials
PF tabular
PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches/hour)1
Average recurrence interval(years)
Duration -
1 2 5 10 25 50 100 200 500 1000
5-min 4.98 5.88 6.84 7.52 8.30 8.84 I 9.32 I 9.76 10.2 I 10.6
(4.58-5.42) (5.41-6.41) (6.26-7.44) (6.89-8.17) (7.57-9.00) (8.02-9.58)i (8.42-10.1) (8.77-10.6) (9.12-11.1) (9.35-11.5)
10-min 3.98 4.70 5.47 6.02 6.61 7.04 7.41 7.73 8.09 8.32
(3.67-4.33) (4.33-5.13) (5.02-5.96) (5.51-6.53) (6.04-7.17) (6.39-7.63) (6.70-8.03) 1 (6.95-8.39) I (7.21-8.80) 1 (7.36-9.06)
15-min 3.32 3.94 4.62 5.07 5.59 5.94 6.24 6.50 6.79 6.96
(3.05-3.60) (3.62-4.30) (4.23-5.03) (4.64-5.51) (5.10-6.06) (5.39-6.44) (5.64-6.76) (5.84-7.05) (6.05-7.38) (6.16-7.58)
30-min 2.27 2.72 3.28 3.68 4.14 4.47 4.78 5.06 5.40 5.64
(2.09-2.47) (2.50-2.97) (3.01-3.57) (3.37-3.99) (3.78-4.49) (4.06-4.85) (4.32-5.18) (4.55-5.49) (4.81-5.87) (4.99-6.14)
60-min 1.42 1.71 2.10 2.39 2.76 3.03 3.29 3.55 3.88 4.12
(1.30-1.54) (1.57-1.86) (1.93-2.29) (2.19-2.60) (2.51-2.99) (2.75-3.29) (2.98-3.57) (3.19-3.85) (3.45-4.21) (3.64-4.48)
2-hr 0.820 0.992 1.23 1.41 1.64 1.82 1.99 2.17 2.39 2.56
(0.752-0.897) (0.908-1.09) (1.12-1.35) (1.29-1.54) (1.49-1.79) (1.64-1.98) (1.79-2.17) (1.93-2.36) (2.11-2.61) (2.24-2.80)
3-h r 0.581 0.701 0.876 1.01 1.19 1.33 1.48 1.62 1.82 1.98
(0.531-0.639) (0.642-0.771) (0.800-0.962)_(0.920-1.11) (1.08-1.30) (1.20-1.45)_ (1.32-1.61) (1.44-1.77) (1.59-1.98) (1.71-2.16)
6-hr 0.351 0.423 0.528 0.611 0.722 0.811 0.902 0.995 1.12 1.22
(0.321-0.385) (0.387-0.464) (0.483-0.579) (0.557-0.668) (0.654-0.788) (0.730-0.883) (0.806-0.981) (0.881-1.08) (0.981-1.22) (1.06-1.33)
12-hr 0.206 0.249 0.313 0.364 0.434 0.490 0.548 0.610 0.695 0.764
(0.189-0.226) (0.229-0.274) (0.287-0.343) (0.332-0.399) (0.393-0.474) (0.440-0.534) (0.488-0.597) (0.537-0.663) (0.602-0.755) (0.652-0.830)I
24-hr 0.123 0.148 0.186 0.216 0.258 0.292 I 0.326 I 0.363 0.413 I 0.453
(0.113-0.133) (0.137-0.161) (0.172-0.202) (0.199-0.235) (0.236-0.280) (0.266-0.317) (0.297-0.354) (0.329-0.394) (0.372-0.449) (0.406-0.494)
2-day 0.072 0.087 0.108 0.125 0.149 0.168 0.187 0.208 0.236 0.259
(0.066-0.078) (0.080-0.094) (0.100-0.117) (0.115-0.136) (0.137-0.161) (0.154-0.182) (0.171-0.203) (0.189-0.226) (0.213-0.257) (0.232-0.282)
3-day 0.051 0.061 0.076 0.088 0.104 0.117 0.130 0.144 0.164 0.179
(0.047-0.055) (0.056-0.066) (0.070-0.082) (0.081-0.095) (0.095-0.112) (0.107-0.126) (0.119-0.141) (0.131-0.156) (0.148-0.178) (0.162-0.195)
4-day 0.040 0.048 0.060 0.069 0.081 0.091 I 0.102 0.112 I 0.128 I 0.140
(0.037-0.043) (0.045-0.052) (0.055-0.064) (0.063-0.074) (0.075-0.088) (0.084-0.099) (0.093-0.110) (0.103-0.122) (0.116-0.138) (0.126-0.152)
7-day 0.026 0.031 0.038 0.044 0.052 0.058 0.064 0.071 0.080 0.087
(0.024-0.028) (0.029-0.034) (0.036-0.041) (0.041-0.047) (0.048-0.055) (0.053-0.062)J(0.059-0.069) (0.065-0.076)1(0.073-0.086) (0.080-0.094)
10-day 0.021 0.025 0.030 0.034 0.040 0.044 0.049 0.053 0.059 0.065
(0.020-0.022) (0.023-0.027) (0.028-0.032) (0.032-0.037) (0.037-0.043) (0.041-0.047) (0.045-0.052) (0.049-0.057) (0.055-0.064)I(0.059-0.069)
20-day 0.014 0.017 0.020 0.022 0.025 0.028 0.031 0.033 0.037 I 0.040
(0.013-0.015) (0.016-0.018) (0.018-0.021) (0.021-0.023) (0.024-0.027) (0.026-0.030) (0.029-0.033) (0.031-0.035) (0.034-0.039)1(0.037-0.042)
30-day 0.011 0.013 0.016 0.017 0.020 0.022 0.023 0.025 0.027 0.029
(0.011-0.012) (0.013-0.014) (0.015-0.017) (0.016-0.018) (0.019-0.021) (0.020-0.023) (0.022-0.025) (0.023-0.027) (0.026-0.029) (0.027-0.031)
45-day 0.009 0.011 0.013 0.014 0.016 0.017 0.018 0.019 0.021 0.022
(0.009-0.010) (0.011-0.012) (0.012-0.013) (0.013-0.015) (0.015-0.017) (0.016-0.018) (0.017-0.019) (0.018-0.021) (0.020-0.022) (0.021-0.024)
60-day 0.008 0.010 0.011 0.012 0.014 0.015 0.016 0.017 0.018 0.019
(0.008-0.009) (0.009-0.010) (0.011-0.012) (0.012-0.013) (0.013-0.014) (0.014-0.015) (0.015-0.016) (0.016-0.017) (0.017-0.019) (0.018-0.020)
1 Precipitation frequency(PF)estimates in this table are based on frequency analysis of partial duration series(PDS).
Numbers in parenthesis are PF estimates at lower and upper bounds of the 90%confidence interval.The probability that precipitation frequency estimates(for
a given duration and average recurrence interval)will be greater than the upper bound(or less than the lower bound)is 5%.Estimates at upper bounds are not
checked against probable maximum precipitation(PMP)estimates and may be higher than currently valid PMP values.
Please refer to NOAA Atlas 14 document for more information.
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PF graphical

NOAA Atlas 14,Volume 2,Version 3
Location name: Monroe, North Carolina, USA* `nonn
Latitude: 35.1289°, Longitude: -80.4961°
Elevation: 536 ft**
�� *source:ESRI Maps " '�
�a en **source:USGS "`.,n,
POINT PRECIPITATION FREQUENCY ESTIMATES
G.M.Bonnin,D.Martin,B.Lin,T.Parzybok,M.Yekta,and D.Riley
NOAA,National Weather Service,Silver Spring,Maryland
PF tabular I PF graphical I Maps & aerials
PF tabular
PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches)1
Average recurrence interval(years)
Duration
1 2 5 10 25 50 _ 100 200 500 1000
5-min 0.415 0.490 0.570 0.627 0.692 0.737 0.777 0.813 0.853 0.881
(0.382-0.452) (0.451-0.534) (0.522-0.620) (0.574-0.681) (0.631-0.750) (0.668-0.798) (0.702-0.842) (0.731-0.882) (0.760-0.927) (0.779-0.959)
10-min 0.663 0.784 0.912 1.00 1.10 I 1.17 1.24 1.29 1.35 1.39
(0.611-0.721) (0.721-0.855) (0.837-0.993) (0.918-1.09) (1.01-1.20) I (1.06-1.27) (1.12-1.34) (1.16-1.40) (1.20-1.47) (1.23-1.51)
15-min 0.829 0.986 1.15 1.27 1.40 1.48 1.56 1.63 1.70 1.74
(0.763-0.901) (0.906-1.07) (1.06-1.26) (1.16-1.38) (1.28-1.52) (1.35-1.61) (1.41-1.69) (1.46-1.76) (1.51-1.84) (1.54-1.90)
30-min 1.14 1.36 1.64 1.84 2.07 2.24 2.39 2.53 2.70 2.82
(1.05-1.24) (1.25-1.48) (1.50-1.78) (1.68-2.00) (1.89-2.24) (2.03-2.42) (2.16-2.59) (2.28-2.74) (2.41-2.94) (2.50-3.07)
60-min 1.42 1.71 2.10 2.39 2.76 3.03 3.29 3.55 3.88 4.12
(1.30-1.54) (1.57-1.86) (1.93-2.29) (2.19-2.60) (2.51-2.99) (2.75-3.29) (2.98-3.57) (3.19-3.85) (3.45-4.21) (3.64-4.48)
2-hr 1.64 1.98 2.46 2.82 3.29 3.64 3.99 4.33 4.78 5.12
(1.50-1.80) (1.82-2.17) (2.25-2.69) (2.57-3.08) (2.98-3.58) (3.29-3.96) (3.59-4.35) (3.87-4.72) (4.23-5.22) (4.49-5.60)
3-hr 1.75 2.11 2.63 3.04 3.58 4.00 4.43 4.87 5.46 5.93
(1.60-1.92) (1.93-2.32) (2.40-2.89)_ (2.76-3.32) (3.24-3.91) (3.60-4.37) (3.96-4.83) (4.32-5.31) (4.79-5.96) (5.14-6.48)
6-hr 2.10 2.53 3.17 3.66 4.33 4.86 5.40 5.96 6.73 7.33
(1.92-2.31) (2.32-2.78) (2.90-3.47) (3.34-4.00) (3.92-4.72) (4.38-5.29) (4.83-5.88) (5.28-6.48) (5.88-7.30) (6.33-7.97)
12-hr 2.49 3.01 3.78 4.39 5.23 5.91 6.61 7.35 8.38 9.21
(2.29-2.73) (2.76-3.31) (3.46-4.14) (4.00-4.81) (4.74-5.71) (5.31-6.44) (5.89-7.19) (6.47-7.99) (7.26-9.10) (7.87-10.0)
24-hr 2.96 3.56 4.48 5.21 6.21 7.01 7.84 8.71 9.92 10.9
(2.73-3.21) (3.30-3.87) (4.13-4.87) (4.79-5.65) (5.69-6.74) (6.40-7.61)_ (7.14-8.52) (7.90-9.47) (8.94-10.8) (9.77-11.9)
2-day 3.47 4.18 5.22 6.04 7.17 8.08 9.02 10.0 11.4 12.4
(3.21-3.76) (3.87-4.54) (4.82-5.66) (5.57-6.54) (6.59-7.77) (7.40-8.75) (8.23-9.78) (9.08-10.9) (10.3-12.4) (11.2-13.6)
3-day 3.68 4.42 5.49 6.34 7.51 8.44 9.41 10.4 11.8 13.0
(3.41-3.98) (4.10-4.78) (5.08-5.94) (5.85-6.85) (6.90-8.11) (7.74-9.13) (8.60-10.2) (9.49-11.3) (10.7-12.8) (11.7-14.1)
4-day 3.89 4.67 5.76 6.63 7.84 8.80 9.80 10.8 12.3 I 13.5
(3.61-4.19) (4.33-5.03) (5.34-6.22) (6.13-7.15)_ (7.22-8.46) (8.09-9.51) (8.98-10.6) (9.89-11.7) (11.2-13.3) (12.2-14.6)
7-day 4.48 5.35 6.52 7.46 8.75 9.78 10.8 11.9 13.5 14.8
(4.19-4.81) (5.01-5.74) (6.10-6.99) (6.96-8.00) (8.13-9.38) (9.07-10.5) (10.0-11.6) (11.0-12.8) (12.4-14.6) (13.5-15.9)
10-day 5.16 6.14 7.39 8.38 9.71 10.8 11.8 12.9 14.4 15.6
(4.84-5.51) (5.75-6.55) (6.92-7.88) (7.83-8.93)_ (9.05-10.3) (10.0-11.5) (11.0-12.6)_ (11.9-13.8) (13.3-15.4) (14.3-16.7)
20-day 6.93 8.18 9.66 10.8 12.4 13.7 14.9 16.2 17.9 19.3
(6.54-7.35) (7.71-8.67) (9.10-10.2) (10.2-11.5) (11.7-13.2) (12.8-14.5) (13.9-15.9) (15.1-17.2) (16.7-19.1) (17.9-20.6)
30-day 8.50 9.99 11.6 12.9 14.6 15.9 17.1 18.4 20.1 21.4
(8.03-8.99) (9.46-10.6) (11.0-12.3) (12.2-13.6) (13.7-15.4)_ (14.9-16.8) (16.1-18.2) (17.2-19.5) (18.8-21.4) (19.9-22.8)
45-day 10.7 12.6 14.4 15.8 17.6 18.9 20.3 21.6 23.3 24.6
(10.2-11.3) (11.9-13.2) (13.6-15.1) (14.9-16.5) (16.6-18.4)_ (17.9-19.9) (19.1-21.3) (20.3-22.7) (21.9-24.6) (23.0-26.0)
60-day 12.8 14.9 16.9 18.4 20.3 21.8 23.2 24.6 26.4 27.7
(12.2-13.4) (14.2-15.6) (16.1-17.6) (17.5-19.2) (19.4-21.3) (20.7-22.8) (22.0-24.4) (23.3-25.8) (24.9-27.8) (26.2-29.2)
1 Precipitation frequency(PF)estimates in this table are based on frequency analysis of partial duration series(PDS).
Numbers in parenthesis are PF estimates at lower and upper bounds of the 90%confidence interval.The probability that precipitation frequency estimates(for
a given duration and average recurrence interval)will be greater than the upper bound(or less than the lower bound)is 5%.Estimates at upper bounds are not
checked against probable maximum precipitation(PMP)estimates and may be higher than currently valid PMP values.
Please refer to NOAA Atlas 14 document for more information.
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PF graphical

PDS-based depth-duration-frequency (DDF) curves
Latitude: 35.1289°, Longitude: -80.4961°
Average recurrence
interval
25 - - (years)
— 1
20 -- 2
a — 5
v 15 — 10
c I — 25
•y
;o — 50
- 100
V
,_ — 200
5 - — 500
-_--- 1.-
--- — 1000
_—
O r i i i t i • i i i i i i
c c c c c - �. �. . L >. >.>, >, >, >, >, >,>,
•- 'E •� '� '- .0 .0 L ••C -c r0 ro ro r0 N to ro ro /0
E N •A lb ry 4 v -1:3-0 -o -0 7 7 77
4' , - M Duration N N 1'6 4 ^ 6 N m y
kri
25 --
c
-- 20 -- • -- Duration
-c
a,a --- 5-min — 2-day
15 -- — 10-min — 3-day
0
'.0 15 min — 4-day
m
�o. 10 - f-- 30 min — 7-day
6 l�� — 60-min — 10-day
a _---_ _ �� — 2fir — 20 day
5 �1v — 3-hr — 30-day
nimnm, 6-hr 45-0ay
0 —I -- 12-hr — 60-day
i i , I , I i 24-hr
1 2 5 10 25 50 100 200 500 1000
Average recurrence interval (years)
NOAA Atlas 14,Volume 2,Version 3 Created(GMT):Fri Dec 22 15:04:33 2023
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Maps & aerials
Small scale terrain

Time of Concentration

-II
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globalwatershed
1 1
r source Esri, Maxar, Earthstarpeoycarhici,ipfi Ifp036§,L a'Community
CLIENT: Union County Prepared by: Prepared for:
Conveyance Swale Drainage Area PROJECT: Grassy Branch WRF Expansion Haze LOCATION: Monroe, North Carolina
(.9
0 37.5 75 150 225 300 375 MAP PCS Exhibit 9101 Southern Pine Blvd. Suite 250
© -- Feet DATA: Charlotte, NC 28273 UNIONCOUNTY
Phone: [phone] WATER
1 inch = 118 feet DATE: March 2024 I Prepared By:ZEK 'Reviewed By: MDP Firm NC License # C-0381
H&S Proj. # 30831-070

PROJECT: Grassy Creek SCS METHODS
SUB-BASIN ID: Basin 1 26 Time of Concentration(min.)
16 Lag Time
SHEET FLOW SEG#1 SEG#2
MANNING'S"n" 0.24
2-YEAR,24-HR. RAIN FALL(IN) 3.56
FLOW LENGTH(FT) 100
ELEV UP(NGVD FT) 564 _
ELEV DOWN(NGVD FT) 561
LAND SLOPE(FT/FT) 0.03 0 HR MIN
TIME OF CONCENTRATION(HRS) 0.19 0 0.19 11.504
SHALLOW CONCENTRATED FLOW SEG#1 SEG#2
SURFACE DESCRIPTION(P OR U) Short Grass Forrest
FLOW LENGTH(FT) 268 299
ELEV UP(NGVD FT) 561 544_
ELEV DOWN(NGVD FT) 544 536
WATERCOURSE SLOPE(FT/FT) 0.063 0.027_ 0
AVERAGE VELOCITY(FT/SEC) 1.75 0.60 0 HR MIN
TIME OF CONCENTRATION(HRS) 0.043 0.138 0 0.18 10.858
TRIANGULAR CHANNEL
CHANNEL FLOW SEG#1 SEG#2 SEG#3 SEG#4 SEG#5
TOP WIDTH(FT) 6_
DEPTH(FT) 1
AREA(SQ. FT) 3 0 0 0 0
WETTED PERIMETER(FT) 6.32 0.00 0 0 0
HYDRAULIC RADIUS(FT) 0.47 0.00 0 0 0
FLOW LENGTH(FT) 1050
ELEV UP(NGVD FT) 538
ELEV DOWN(NGVD FT) 514
CHANNEL SLOPE(FT/FT) 0.023 0.000 0 0 0
MANNING'S"n" 0.03
AVERAGE VELOCITY(FT/SEC) 4.56 0.00 0 0 0
TIME OF CONCENTRATION(HRS) 0.064 0.00 0 0 0 0.06 TIME OF CONCENTRATION(MIN)
TIME OF CONCENTRATION(MIN) 3.8 0.0 _
TOTAL TIME OF CONCENTRATION(HRS) 0.44 26 MIN.
LAG TIME(HRS) 0.26 16 MIN.

Diversion Swale for Post Construction

Channel Calculations-Diversion Swale
Project: Grassy Branch WRF Expansion
Client: Union County
Location: Union County,NC
Objective: Design channel to convey flow in a non erosive manner
References: (1) North Carolina Erosion and Sediment Control Planning and Design Manual
(2) Elements of Urban Stormwater Design,H.R.Malcom.
Procedure: Use procedures outlined in the above reference. Rational Method will be used to calculate
flows. Normal depth will be calculated using Mannings Equation and water velocity will be
calculated using the principle of continuity(Q=VA)
Channels will be designed to carry flow generated by the 10-Year storm event using
maximum slope.
Calculations: Post-Developed
Rational Method: Q=C*I*A
Where
Q=Flow(cfs)
C=Runoff Coefficient
I=Rainfall Intensity(in/hr)
A=Drainage Area(ac)
Find C value in Reference 2
Find Intensity for 10-year event in Reference 2
C= 0.39
I= 4.05
Drainage area(A)(ac)= 18.688
Q(cfs)= 29.5 10-year design storm
Check channel for adequate depth and for need for armoring
Assume 2.5 ft/s as maximum allowable velocity for bare earth and 4.5 ft/s
as maximum allowable velocity for grass lined
Design channel lining using tractive force procedure
Calculations will be done using Manning's Equation to find normal depth
and Continuity(Q=V*A)to find velocity.
Q(cfs)= 29.5
S,, 5(eft)=0.017
B(ft)= 0
M(ft)= 3
Channel cross section
Calculate normal depth and velocity with bare earth as lining
From Ref.2, n= 0.02
Flow(cfs)= 29.5
Hormel depth(ft)= 1.2
velocity(ft/s)
= 6.71
Since velocity is greater than the 2.5 ft/s limit for bare earth, M M
TEMPORARY OR PERMANENT LINING WILL BE REQUIRED
Calculate normal depth and velocity with grass as lining
From Ref.2, n= 0.03
Flow(cfs)= 29.5
normal depth(ft)= 1.4
velocity(ft/s)= 4.95
Since velocity is greater than the 4.5 ft/s limit for grass lined,
PERMANENT LINING WILL BE REQUIRED
Perm-Temp Channel-Grassy Branch May 2024

Calculate normal depth and velocity for PERMANENT LINING
From product manual,n= 0.031
Flow(cfs)= 29.5
normal depth(ft)= 1.4
velocity(ft/s)= 4.83
Calculate shear stress
Shear stress(Ib/ft2)=(62.4 Ib/ft3)*(normal depth)*(slope)
shear stress(lb/ft 2 )= 1.51
Use permanent lining with a minimum shear stress
shear stress(Ib/ft2)= 2.00
Max Permissible Shear Max Velocity
Unvegetated Vegetated Unvegetated Vegetated
Lining Type Manufaturer and Model 'n' lbs/ft2 lbs/ft2 ft/s ft/s
Straw w/Net-RECM North American Green-S150 0.044 1.75 N/A 6.00 N/A
Coconut Fiber-RECM North American Green-C125 0.019 2.25 N/A 10.00 N/A
Polypropylene Mat-TRM North American Green-P300 0.029 3.00 8.00 9.00 16.00
Polypropylene Mat-TRM North American Green-P550 0.031 4.00 14.00 12.50 25.00
1 n value interpolated for normal depth of 1.0 ft
Temporary shear stress:1.75-2 lbs/sf
Permanent shear stress:2 lbs/sf
Perm-Temp Channel-Grassy Branch May 2024

USGS StreamStats Peak Flow

Grassy Branch WRF-StreamStats Report
Region ID: NC
Workspace ID: NC2024O1O4175934687OOO
Clicked Point (Latitude, Longitude): 35.13067,-80.49433
Time: 2024-01-04 13:00:03-0500
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Grassy Branch WRF 1629 Old Fish Rd,Monroe,NC Peak Flow
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Basin Characteristics
Parameter Code Parameter Description Value Unit
DRNAREA Area that drains to a point on a stream 0.0292 square miles
LCO6IMP Percentage of impervious area determined from NLCD 2006 impervious dataset 0.81 percent
PCTREG1 Percentage of drainage area located in Region 1 - Piedmont/ Ridge and Valley 100 percent
PCTREG2 Percentage of drainage area located in Region 2- Blue Ridge 0 percent
PCTREG3 Percentage of drainage area located in Region 3 -Sandhills 0 percent
PCTREG4 Percentage of drainage area located in Region 4- Coastal Plains 0 percent
PCTREG5 Percentage of drainage area located in Region 5- Lower Tifton Uplands 0 percent
Peak-Flow Statistics
Peak-Flow Statistics Parameters [Region 1 Piedmont rural under 1 sqmi 2014 5030]
Parameter Code Parameter Name Value Units Min Limit Max Limit
DRNAREA Drainage Area 0.0292 square miles 0.1 1
LCO6IMP Percent Impervious NLCD2OO6 0.81 percent 0 47.9

Peak-Flow Statistics Parameters [Peak Southeast US NC 2023 5006]
Parameter Code Parameter Name Value Units Min Limit Max Limit
PCTREG1 Percent Area in Region 1 100 percent 0 100
PCTREG2 Percent Area in Region 2 0 percent 0 100
PCTREG3 Percent Area in Region 3 0 percent 0 100
PCTREG5 Percent Area in Region 5 0 percent 0 100
DRNAREA Drainage Area 0.0292 square miles 0.08 8902
PCTREG4 Percent Area in Region 4 0 percent 0 100
Peak-Flow Statistics Disclaimers [Region 1 Piedmont rural under 1 sqmi 2014 5030]
One or more of the parameters is outside the suggested range.Estimates were extrapolated with unknown errors.
Peak-Flow Statistics Flow Report [Region 1 Piedmont rural under 1 sqmi 2014 5030]
Statistic Value Unit
50-percent AEP flood 13.6 ft^3/s
20-percent AEP flood 21.5 ft^3/s
10-percent AEP flood 27 ft^3/s
4-percent AEP flood 33.8 ft^3/s
2-percent AEP flood 39 ft^3/s
1-percent AEP flood 44.2 ft^3/s
0.5-percent AEP flood 49.2 ft^3/s
0.2-percent AEP flood 58.5 ft^3/s
Peak-Flow Statistics Disclaimers [Peak Southeast US NC 2023 5006]
One or more of the parameters is outside the suggested range.Estimates were extrapolated with unknown errors.
Peak-Flow Statistics Flow Report [Peak Southeast US NC 2023 5006]
Statistic Value Unit
50-percent AEP flood 15.2 ft^3/s
20-percent AEP flood 28.7 ft^3/s
10-percent AEP flood 40 ft^3/s
4-percent AEP flood 55.9 ft^3/s
2-percent AEP flood 70.3 ft^3/s
1-percent AEP flood 85 ft^3/s
0.5-percent AEP flood 100 ft^3/s
0.2-percent AEP flood 121 ft^3/s
Peak-Flow Statistics Citations
Feaster,T.D., Gotvald,A.J., and Weaver,J.C.,2014, Methods for estimating the magnitude and frequency of floods for urban and
small, rural streams in Georgia, South Carolina, and North Carolina, 2011 (ver. 1.1, March 2014): U.S.Geological Survey Scientific
Investigations Report 2014-5030, 104 p. (http://pubs.usgs.gov/sir/2014/5030/)
Feaster,T.D., Gotvald,A.J., Musser, J.W., Weaver,J.C, Kolb, K.R., Veilleux,A.G., and Wagner, D.M.2023, Magnitude and frequency
of floods for rural streams in Georgia, South Carolina, and North Carolina, 2017—Results: U.S. Geological Survey Scientific
Investigations Report 2023-5006, 75 p. (https://pubs.er.usgs.gov/publication/sir20235006)

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Application Version:4.19.2
StreamStats Services Version:1.2.22
NSS Services Version:2.3.2

Culvert Calculations

Culvert Report
Hydraflow Express Extension for Autodesk®Civil 3D®by Autodesk, Inc. Thursday,Jun 13 2024
Circular Culvert
Invert Elev Dn (ft) = 512.91 Calculations
Pipe Length (ft) = 22.00 Qmin (cfs) = 29.50
Slope (%) = 0.50 Qmax (cfs) = 29.50
Invert Elev Up (ft) = 513.02 Tailwater Elev (ft) = (dc+D)/2
Rise (in) = 30.0
Shape = Circular Highlighted
Span (in) = 30.0 Qtotal (cfs) = 29.50
No. Barrels = 1 Qpipe (cfs) = 29.50
n-Value = 0.012 Qovertop (cfs) = 0.00
Culvert Type = Circular Concrete Veloc Dn (ft/s) = 6.51
Culvert Entrance = Square edge w/headwall (C) Veloc Up (ft/s) = 7.57
Coeff. K,M,c,Y,k = 0.0098, 2, 0.0398, 0.67, 0.5 HGL Dn (ft) = 515.09
HGL Up (ft) = 514.87
Embankment Hw Elev (ft) = 516.13
Top Elevation (ft) = 518.70 Hw/D (ft) = 1.24
Top Width (ft) = 11.00 Flow Regime = Inlet Control
Crest Width (ft) = 20.00
Elev(tt) <Name> Hw Depth(ft)
519.00 I I 5.98
518.00 4.98
I
517.00 3.98
516.00 Inlet control 2.98
515.00 1.98
514.00 0.98
513.00 -0.02
512.00 -1.02
511.00 -2.02
0 5 10 15 20 25 30 35 40 45
GrculerCulvert HOL Embank
Reach(8)

Riprap Outlet Protection Calculations

DESIGN OF RIPRAP OUTLET PROTECTION
User Input Data
Calculated Value
Reference Data
Designed By: CAB Date: 1/24/24
Checked By: CJM Date: 6/13/24
Company: Hazen and Sawyer, P.C.
Project Name: Grassy Branch WRF
Project No.: 30831-070
Site Location (City/Town) Union, NC
Temporary and
Culvert Id. Permanent Diversion
Swales
Total Drainage Area (acres) 18.688
Step 1. Determine the tailwater depth from channel chztracteristics below the
pipe outlet for the design capacity of the pipe. If the tailwater depth is less
than half the outlet pipe diameter_ it is classified minimum tailwater condition.
If it is greater than half the pipe diameter. it is classified maximum condition.
Pipes that outlet onto wide Hat areas with no defined channel are assumed
to have a minimum tailwater condition unless reliable flood stage elevations
show otherwise.
Outlet pipe diameter, Do (in.) 30
Tailwater depth (in.) 26
Minimum/Maximum tailwater? Max TW (Fig. 8.06b)
Discharge (cfs) 29.5
Velocity (ft./s) 6.32
Step 2. Based on the tailwater conditions determined in step 1. enter Figure
8.06a or Figure 8.06b. and determine d;,_riprap size and minimum apron length
(La). The d;. size is the median stone size in a well-graded nprap apron.
Step 3. Determine apron width at the pipe outlet. the apron shape. and the
apron width at the outlet end from the same figure used in Step 2.

Minimum TW Maximum TW
Figure 8.06a Figure 8.06b
Riprap d50, (ft.) 0.5 0.1
Minimum apron length, La (ft.) 16 12
Apron width at pipe outlet (ft.) 7.5 7.5
Apron shape wedge wedge
Apron width at outlet end (ft.) 18.5 7.3
step 4. Determine the maximum stone diameter:
= i .5 x d c 0
Minimum TW Maximum TW
Max Stone Diameter, dmax (ft.) 0.75 0.15
Step 5. Determine the apron thickness:
Apron thickness = 1.5 x
Minimum TW Maximum TW
Apron Thickness(ft.) 1.125 0.225
Step 6. Fit the riprap apron to the site by making it level for the minimum
length, La. from Figure 8.06a or Figure 8.06b. Extend the apron farther
downstream and along channel banks until stability is assured. Keep the
apron as straight as possible and align it with the flow of the receiving stream.
Make any necessary alignment bends near the pipe outlet so that the entrance
into the receiving stream is straight.
Some locations may require lining of the entire channel cross section to assure
stability.
It may be necessary to increase the size of riprap where protection of the
channel side slopes is necessary (Appendix S.05). Where overfalls exist at
pipe outlets or flows are excessive, a plunge pool should be considered, see
page 8.06.8_
Recommended Riprap Apron Size
Apron Length (ft.) 12
Apron Width (ft.) 8
Thickness of Stone (ft.) 1.1
NCDOT Stone Class Class 1

Figure 8.06a: Design of outlet protection from a round pipe flowing full,
minimum tailwater condition (Tw<0.5 diameter)
30
Outlet W • Do + L a 90 1-
•
pipe ' . •
diameter (Do)
La _.1 50 - --�..__.. '�igh
w ter 0.500 i : 1. ::.I / r
PO
ve
t•P -.:It _ '11 I •
i . I' 1 • -, . 4, .er'4
•
,•,4 1 M Il11:111'I iii u .A 'g .0 t . .
011 1111111 : i1111 ir/Aliiril
10 -. :..: :::: - �:,. !rnit .• •O
.ii
. Ater
- 25 ,i i 1 1 ri I.211r1r: Asee ! E
v , 15 sue/. 11."-
I 0
v = 5 �...•
3 5 10 20 51 100 200 500 1000
Discharge(tt3/sec)
Curves may not be extrapolated
Figure 8.06a Design of outlet protection protection from a round pipe flowing full,minimum tailwater condition(Tw<0-5 diameter)
Rev.12 93 8.06.3

Figure 8.06b: Design of outlet protection from a round pipe flowing full, maximum
tailwater condition (Tw>=0.5 diameter)
3D0
}Outlet U = Do + 0.4La 120 1-pipe t f I
diameter(Do);r-- la I 110 r .
;-
Q Tai l•!_a_w 3 2.5D0 ( l •
100 r
. i i A
/ . •
oC
Q 70 --.--- v _a
ec'se 60 r
v 1 tiii: , o
/50H
a .I
40 ... I . , 3
30 .t.. , b : .. . .1Ir ',.. if : . .. ._. • _ t
, , ,
. . ... . .. . .. ..
.4 , ../g . ! ,.. , _...... , 07ArrAisi:47., 2 :a.,
20 1. , , . g reprirkilir Afil
l /./ "P. .4
v= is. � �. ,
5 � o
1 *:•43 :
V g 10 6 LAIIPACII0j10. 00°F..,4100r,eidOrArdjrir* * * I
1 .
tiT
3 5 10 20 50 100 200 500 1000
Discharge(ft3/sec)
Curves may not be extrapolated.
Figure 8.06b Design of outlet protection from a round pipe flowing full.maximum tailwater condition(T. >0 5 diameter)
8.06..1 Rev.11'93