Pages from OutfallAnalysis_HYD_R5759.pdf

DRAINAGE OUTFALL ANALYSIS #7
Location: Channel located 32' downstream of STIR. 1352 at proposed right of way.
-L- 139+91 (o/s - 153' RT)
Project: R-5759 County: Wilkes
Pre -Construction Drainage Area
Hydraulic Method:
Total Drainage Area =
Total Drainage Area within
Proposed NCDOT ROW
Project Limits =
Weighted C- Value=
Time of concentration =
Rational
(ac.)
(so.)
(unitless)
(min.)
102.63
14.07
0.43
30
Sub -Areas
C-Value
DA (acres)
Impervious within NCDOT ROW
0.9
4.19
Grass within NCDOT ROW
0.3
9.89
Woodland outside NCDOT ROW
0.1
Business outside NCDOT ROM
0.6
36.23
Residential outside NCDOT ROW
0.3
52.32
TOTAL
102.63
Rainfall Intensities
12= 2.35 in/hr
Is= 2.88 in/hr
Igo= 3.28 in/hr
Peak Discharges
Qz=
103.8 cfs
QI-
127.2 cfs
Q1,
144.91 cfs
)ESIGN NOTES: Bigger drainage area in proposed condition due to more drainage area is being diverted to Str. 1330.
assumption: Payment removal along Y30 will be seeded.
Date: 12/10/2021
Post -Construction Drainage Area
Hydraulic Method:
Total Drainage Area =
Total Drainage Area within
Proposed NCDOT ROW
Project Limits =
Weighted C- Value=
Time of concentration =
Analysis by:
Analysis checked by:
Rational
103.39 (ac.)
14.71 (ac.)
0.45 (unitless)
30 (min.)
MYC
ATH
Sub -Areas
C-Value
DA (acres)
Impervious within NCDOT ROW
0.9
7.80
Grass within NCDOT ROW
0.3
6.91
Woodland outside NCDOT ROW
0.1
Business outside NCDOT ROW
0.6
36.23
Residential outside NCDOT ROW
0.3
52.44
TOTAL
103.39
Rainfall Intensities
1z= 2.35 in/hr
Is= 2.88 in/hr
Ilo= 3.28 in/hr
Peak Discharges
Qs
Qs=
=
Qio=
Discharge Comparison Table
Q Difference
(cfs)
M
2-Year
5.63
5.43%
5-Year
6.901
5.43%
10-Year
7.861
5.43%
Pre -Construction Drainage Outlet Channel Description Post -Construction Drainage Outlet Channel Description
Base Width 9 (ft.) Base Width 9 (ft.)
Sideslope (LT) 1 (H:V=1) Sideslope (LT) 1 (H:V=1)
Sideslope (RT) 1 (H:V=1) Sideslope (RT) 1 (H:V=1)
Channel Slope 0.029 (ft./ft.) Channel Slope 0.029 (ft./ft.)
Manning's n-Value 0.045 (unitless) Manning's n-Value 0.045 (unitless)
Pre -Construction Outlet Channel Hydraulics Post -Construction Outlet Channel Hydraulics Outlet Channel Hydraulics Comparison Table
Depth
Velocity
Shear Stress
(ft)
(fps)
(psf)
2-Year
1.54
9.06
2.79
5-Year
1.73
9.55
3.13
10-Year
1.87
9.87
3.38
SUMMARY AND RECOMMENDATIONS: No actions required
Depth
Velocity
Shear Stress
(ft)
(fps)
(psf)
2-Year
1.59
9.21
2.88
5-Year
1.79
9.70
3.24
10-Year
1.93
10.03
3.49
109.4 cfs
134.1 cfs
152.7 cfs
Depth
Depth
Velocity
Velocity
Shear Stress
Shear Stress
(ft)
(fps)
(psf)
2-Year
0.05
3.25%
0.15
1.66%
0.09
3.25%
5-Year
0.06
3.47%
0.15
1.57%
0.11
3.47%
10-Year
0.06
3.21%
0.16
1.62%
0.11
3.21%

y =�
IN
c
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existing • 1
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i h
I
1 c i