HomeMy WebLinkAboutWPO202200021 Calculations 2022-08-08STOCKTON CREEK SUBDIVISION VSMP
STORMWATER MANAGEMENT CALCULATIONS
PACKET
Date of Calculations
May 20, 2022
PREPARED BY:
COLLINS ENGIkI=ERING
200 GARRETT STREET, SUITE K
CHARLOTTESVILLE, VA 22902
434.293.3719 PH
434.293.2813 FX
www.collins-engineering.com
SCS TR-55 Calculations
Si " . .
!Database)
Soils Table (Source: NRCS Web Soil Survey Online Database)
Note: The soils' properties witin this development are predominantly composed of hydrologic group
type B soils.
Albemarle County, Virginia(VA003)
81B Thurmont
2.9%
Albemarle
County, Virginia (VA003) ®
loam, 2 to 7
percent slopes
Map Unit
m Sybol
Map Unit Name
portent of
Portent
81C Thurmont
7.1%
4D
Ashe loam, 15
1.0%
loam, 7 to 15
to 25 percent
percent slopes
slopes
89B Unison silt
14.2 %
4E
Ashe loam, 25
8.4%
loam, 2 to 7
to 45 percent
percent slopes
slopes
89C Unison silt
6.1 %
7B
Braddock
10.1%
loam, 7 to 15
percent slopes
loam, 2 to 7
percent slopes
Totals for Area of
100.0%
Interest
14D
Chester loam,
25.5%
15 to 25
percent slopes
14E
Chester loam,
4.7%
25 to 45
percent slopes
36B
Hayesville
6.6%
loam, 2 to 7
percent slopes
36C
Hayesville
13.6%
loam, 7 to 15
percent slopes
Precipitation Data
(Source: NOAA's National Weather Service, Hydrometerorological Design Studies Center, Atlas 14
Point Precipitation Frequency Estimates)
POINT PRECIPITATION FREQUENCY (PF) ESTIMATES
WITH 90%CONFIDENCE INTERVALS AND SUPPLEMENTARY INFORMATION
NOAA Atlas 14, Volume 2, Version 3
PDS-based precipitation frequency estimates with 90% confidence intervals (in inches)l
AvmsOe Aunana inNrval ay )
0ura0°^
000 10 ®® 100 ®® 1000
241r QW331) 1 (32544.01) 1 (0 1-0) 1 (48 5.90) 1 (5-W729) I (6 14Q) 1 (T 9S3) 1 (900.110) I (88& 10) 1 (11 -0V) I
O Terrain
Old Ti�nPike Rd
y
j
n
v
Rockfish GOP
o I0
0 I
t5J
200mIL
4 600
a
POINT PRECIPITATION FREQUENCY (PF) ESTIMATES
WITH 90%CONFIDENCE INTERVALS AND SUPPLEMENTARY INFORMATION
NOAA Atlas 14, Volume 2, Version 3
U.S. Department of Agriculture
Natural Resources Conservation Service
Project: Stockton Creek Residential Development
Location: Rte 151 and Goodloe Lane
Check One: Present X Developed
1. Runoff curve Number (CN)
TR 55 Worksheet 2: Runoff Curve Number and Runoff
Designed By: UMW, PE
Checked By: SRC, PE
FL-ENG-21A
06/04
Date: 7/28/2022
Date: 7/28/2022
Cover description
CN (weighted) _Area
Drainage Area
Soil name and hydrologic
(Cover type, treatment, and hydrologic condition; percent
CN
Product of CN x
total product/
Calculated'S'
Description
group (Appendix A)
(Acres)
Area
Value
impervious; unconnected/ connected impervious area ratio)
total area
Impervious Areas
98
0.21
20.9
DA A
B
Lawns in Good Condition (25%+/-)
61
14.08
858.7
61
6.33
(Pre-ReDev.)
Woods Grass Good Condition
58
1.44
83.5
Impervious Areas
98
2.64
258.4
DAA
B
Lawns in Good Condition (25%+/-)
61
12.71
775.5
67
4.90
(Post-ReDev)
Woods Grass Good Condition
1 58
1 0.38
1 22.0
2. Runoff
1-Year Storm
2-Year Storm
30-Year Storm
100-Year Storm
I Drainage Area Description
Frequency -years
1
2
10
100
n/a
Rainfall, P(24 hour) -inches
2.97
3.6
5.38
8.69
n/a
Ea
Runoff, Q-inches
0.36
0.63
1.62
4.01
DA A(Pre-ReDev)
Runoff, Q-inches
0.58
0.91
2.08
4.72
DA A(Post-ReDev)
U.S. Department of Agriculture
Natural Resources Conservation Service
TR 55 Worksheet 3: Time of Concentration (TJ or Travel Time (TJ
Project: Stockton Creek Residential Development Designed By:
Location: Rte 151 and Goodloe Lane Checked By:
Check One: Present X Developed X
Check One: Tc X Tt
Segment
Sheet Flow: (Applicable to Tc only)
DA A DA A
(Pre-ReDev.) I (Post-ReDev)
1 Surface description (Table 3-1)
Grass -dense Grass -dense
2 Manning's roughness coeff., n (Table 3-1)
0.24 0.24
3 Flow length, L (total L < 100) (ft)
46 46
4 Two-year 24-hour rainfall, Pz (in.)
3.60 3.60
5 Land slope, s (ft/ft)
0.02 0.02
6 Compute Tt = [0.007(n*L)08] / P205 s°a
0.12 0.12
Shallow Concentrated Flow
7 Surface description (paved or unpaved)
Unpaved Unpaved
8 Flow Length, L (ft)
954 583
9 Watercourse slope, s (ft/ft)
0.03 0.01
30 Average velocity, V (Figure 3-1) (ft/s)
2.8 1.9
11 T,= L/3600*V
0.10 0.09
Channel Flow:
12 Cross sectional flow area, a (ft)
0
w
13 Wetted perimeter, Pw (ft)
a
14 Hydraulic radius, r=a/Pw (ft)
z
15 Channel Slope, s (ft/ft)
O LL
J
W
16 Manning's Roughness Coeff, n
z
z/a os
=
18 Flow length, L (ft)
m
LD
19 T,= L / 3600*V
0.02
20 Watershed or subarea TcorTt
(Add Tt in steps 6, 11 and 19)
0.22 0.23
U.S. Department of Agriculture
Natural Resources Conservation Service
Project:
Location:
Check One:
TR 55 Graphical Peak Discharge Method
Stockton Creek Residential Development
Rte 151 and Goodloe lane
Presen% Dew%
Designed By: LMW, PE
Checked By: SRC, PE
1. Data
Drainage Area Description
Drainage Area Description
DA A
(Pre-ReDev.)
DA A
(Post-ReDev)
Drainage Area (Am) in miles'
0.0246
0.0246
Runoff curve number CN=
61
67
Time of concentration (Tc)=
0.22
0.23
Rainfall distribution type=
Type II
Type II
Pond and swamp areas spread
throughout the watershed=
0
0
2. Frequency -years
1 2 10 100
1
2 10
100
3. Rainfall, P (24 hour)- inches
2.97 3.6 5.38 8.69
2.97
3.6 5.38
8.69
4. Initial Abstraction, la- inches
1.27 1.27 1.27 1.27
0.98
0.98 0.98
0.98
5. Compute la/P
0.43 0.35 0.24 0.15
0.33
0.27 0.18
0.11
6. Unit peak discharge, Qu-um/in
See Hydrograph for Flows
Routed through Detention Basin
7. Runoff, Q from Worksheet 2-inches
0.36 0.63 1.62 4.01
0.58
0.91 2.08
4.72
8. Pond and Swamp adjustment factor, Fp
1 1 1 1
1
1 1
1
9. Peak Discharge, Op-cfs
where Qp=Qu Am Q Fp
1 3.94
8.94
27.72
73.56
1 1.78
8.47
24.83
85.72
WATERSHED SUMMARY FOR CHANNEL AND FLOOD PROTECTION
Area,
1-year Flow,
2-year Flow,
10-year Flow,
100-year Flow,
CN
ac.
cfs
cfs
cfs
cfs
DAA(Pre-ReDev)
61 15.73
3.94
8.94
27.72
73.56
DAA(Post-ReDev)
67 15.73
1.78
8.47
24.83
85.72
Date: 7/28/2022
Date: 7/28/2022
Pre-ReDevelopment Site
Flow Hydrographs
The following inflow hydrographs reflect the pre -redevelopment onsite concentrated flow from
Subarea A.
Worksheet 5b (Modified for Clarity): Basic watershed Data
1-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below
Subarea Tc (hrs.) Tt (hr.) la / P Am'Q (miz-in)
DA A 0.22 0.22 0.43 0.0089
(Pre-ReDev.)
Hydrograph Time (hrs.)
1-yr
Discharges
(cfs)
0.0
0.00
11.0
0.00
11.3
0.00
11.6
0.00
11.9
0.10
12.0
0.52
12.1
1.99
12.2
3.94
12.3
3.42
12.4
2.31
12.5
1.77
12.6
1.47
12.7
1.25
12.8
1.08
13.0
0.91
13.2
0.81
13.4
0.73
13.6
0.68
13.8
0.62
14.0
0.58
14.3
0.51
14.6
0.49
15.0
0.46
15.5
0.42
16.0
0.38
16.5
0.35
17.0
0.34
17.5
0.32
18.0
0.31
19.0
0.28
20.0
0.24
22.0
0.22
26.0
0.00
SCS TR-55 Pre-ReDevelopment Unit
Hydrograph (ON DA A)
Worksheet 5b (Modified for Clarity): Basic watershed Data
2-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below
Subarea Tc (hrs.) Tt (hr.) la / P Am'Q (miz-in)
DA A 0.22 0.22 0.35 0.0154
Hydrograph Time (hrs.) 2-yr
Discharges
0.0
0.00
11.0
0.00
11.3
0.00
11.6
0.00
11.9
0.39
12.0
1.84
12.1
5.95
12.2
8.94
12.3
7.16
12.4
4.51
12.5
3.27
12.6
2.61
12.7
2.15
12.8
1.82
13.0
1.51
13.2
1.32
13.4
1.19
13.6
1.09
13.8
1.00
14.0
0.92
14.3
0.81
14.6
0.77
15.0
0.72
15.5
0.66
16.0
0.59
16.5
0.54
17.0
0.51
17.5
0.49
18.0
0.47
19.0
0.41
20.0
0.36
22.0
0.33
26.0
0.00
6
5
a
3
2
1
0
SCS TR-55 Pre-ReDevelopment Unit
Hydrograph (ON DA A)
Worksheet 5b (Modified for Clarity): Basic watershed Data
10-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below
Subarea Tc (hrs.) Tt (hr.) la / P Am'Q (miz-in)
DA A 0.22 0.22 0.24 0.0398
(Pre-ReDev.)
Hydrograph Time (hrs.)
10-yr
Discharges
(cfs)
0.0
0.00
11.0
0.27
11.3
0.36
11.6
0.55
11.9
3.21
12.0
8.78
12.1
21.68
12.2
27.72
12.3
20.49
12.4
12.17
12.5
8.37
12.6
6.45
12.7
5.19
12.8
4.33
13.0
3.51
13.2
3.04
13.4
2.71
13.6
2.47
13.8
2.25
14.0
2.05
14.3
1.80
14.6
1.68
15.0
1.56
15.5
1.42
16.0
1.27
16.5
1.15
17.0
1.08
17.5
1.04
18.0
0.97
19.0
0.86
20.0
0.74
22.0
0.67
26.0
0.00
6
s
4
3
2
1
0
SCS TR-55 Pre-ReDevelopment Unit
Hydrograph (ON DA A)
Worksheet 5b (Modified for Clarity): Basic watershed Data
100-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below
Subarea Tc (hrs.) Tt (hr.) la / P Am'Q (miz-in)
DA A 0.22 0.22 0.15 0.0985
(Pre-ReDev.)
Hydrograph Time (hrs.)
100-yr
Discharges
(cfs)
0.0
0.00
11.0
1.65
11.3
2.24
11.6
3.38
11.9
14.91
12.0
31.14
12.1
62.23
12.2
73.56
12.3
51.01
12.4
29.22
12.5
19.38
12.6
14.66
12.7
11.59
12.8
9.62
13.0
7.66
13.2
6.61
13.4
5.85
13.6
5.31
13.8
4.80
14.0
4.37
14.3
3.83
14.6
3.57
15.0
3.29
15.5
2.97
16.0
2.64
16.5
2.35
17.0
2.22
17.5
2.12
18.0
2.00
19.0
1.77
20.0
1.48
22.0
1.35
26.0
0.00
6
s
a
3
2
1
0
SCS TR-55 Pre-ReDevelopment Unit
Hydrograph (ON DA A)
Channel and Flood Protection Calculations
The following calculations shows how Subarea A meets Channel and Flood Protection requirements.
9 VAC 25-870-66
Section B: Channel Protection Utilizing a 6-inch Orifice
"Concentrated stormwater flow shall be released into a stormwater conveyance system and shall meet
the criteria in subdivision 1, 2 or 3 of this subsection..."
Section B.1: Manmade stormwater conveyance systems
"When stormwater from a development is discharged to a manmade stormwater conveyance system,
following the land -disturbing activity, either..." a. or b. shall be met:
Section B.l.b.
"The peak discharge requirements for concentrated stormwater flow to natural stormwater conveyance
systems in subdivision 3 of this subsection shall be met."
Section 8.3
"... the maximum peak flow rate from the one-year 24-hour storm following the land -disturbing activity
shall be calculated either.." a. or b."
Section 6.3.a.
In accordance with the following methodology:
Q Allowed < I.F. * (Q Pre�Developed + (RV Pre -Developed) ) I (RV Developed )
Q Allowed <
1.98 cfs
Where: QPre-Developed=
3.94cfs
(FromTR-55)
CN Pre�Devebped=
61
(From Curve Number Summary)
S Pre -Developed =
6.33
(From SCS TR-55 eq. 2-4)
RV Pre�Developed=
0.36 in.
(From SCSTR-55 eq. 2-3)
CN Pt -Developed =
67
(From Curve Number Summary)
S P.A Developed =
4.90
(From SCS TR-55 eq. 2-4)
RV port -Developed=
0.58 in.
(From SCS TR-55 eq. 2-3)
I.F. =
0.80
(Factor of Safety)
Q Developed =
1.78 cfs
Section B.4 Limits of Analysis
The analysis terminates at Post -Development Subarea A since subsection B.3.a is met.
9 VAC 25-870-66
Section C: Flood Protection
"Concentrated stormwater flow shall be released into a stormwater conveyance system and shall meet one of the following
criteria as demonstrated by use of acceptable hydrologic and hydraulic methodologies:"
Section C.2.b.:
The point of discharge (Detention Basin B's Outfall), "releases a postdevelopment peak flow rate for the 10-year 24-hour storm
event that is less than the predevelopment peak flow rate from the 10-year 24-hour storm event. Downstream stormwater
conveyance systems do not require any additional analysis to show compliance with flood protection criteria if this option is
utilized."
10-Year, 24-Hour Pre-ReDevelopment Subarea A Peak Flow Rate = 27.72 cfs
10-Year, 24-Hour Post-ReDevelopment Subarea A Peak Flow Rate = 24.83 cfs
Section C.3 Limits of Analysis
The flood protection analysis terminates at Subarea A since subsection C.2.b is met.
Post -Re Development Detention Basin
Routings and Outflow Hydrographs
The following routing calculations and outflow hydrographs reflect the post -redevelopment
attenuation in Subarea A from the proposed detention basin.
Worksheet 5b (Modified for Clarity): Basic watershed Data
1-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below
Subarea Tc (hrs.) Tt (hr.) la / P Am'Q (miz-in)
DA A 0.23 0.23 0.33 0.0141
(Post-ReDev)
Hydrograph Time (hrs.)
1-yr
Discharges
(cfs)
0.0
0.00
11.0
0.00
11.3
0.00
11.6
0.00
11.9
0.37
12.0
1.76
12.1
5.65
12.2
8.41
12.3
6.92
12.4
4.46
12.5
3.17
12.6
2.48
12.7
2.02
12.8
1.70
13.0
1.38
13.2
1.20
13.4
1.08
13.6
0.99
13.8
0.90
14.0
0.83
14.3
0.73
14.6
0.68
15.0
0.64
15.5
0.58
16.0
0.52
16.5
0.48
17.0
0.45
17.5
0.43
18.0
0.41
19.0
0.36
20.0
0.32
22.0
0.29
26.0
0.00
SCS TR-55 Post-ReDevelopment Unit
Hydrograph (ON DA A)
Worksheet 5b (Modified for Clarity): Basic watershed Data
2-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below
Subarea Tc (hrs.) Tt (hr.) la / P Am'Q (miz-in)
DA A 0.23 0.23 0.27 0.0225
Hydrograph Time (hrs.) 2-yr
Discharges
0.0
0.00
11.0
0.07
11.3
0.10
11.6
0.15
11.9
1.20
12.0
3.96
12.1
10.91
12.2
14.89
12.3
11.74
12.4
7.34
12.5
5.06
12.6
3.88
12.7
3.12
12.8
2.59
13.0
2.08
13.2
1.80
13.4
1.60
13.6
1.46
13.8
1.33
14.0
1.22
14.3
1.07
14.6
0.99
15.0
0.93
15.5
0.84
16.0
0.75
16.5
0.68
17.0
0.65
17.5
0.62
18.0
0.58
19.0
0.51
20.0
0.44
22.0
0.40
26.0
0.00
6
s
4
3
2
1
0
SCS TR-55 Post-ReDevelopment Unit
Hydrograph (ON DA A)
Worksheet 5b (Modified for Clarity): Basic watershed Data
10-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below
Subarea Tc (hrs.) Tt (hr.) la / P Am'Q (miz-in)
DA A 0.23 0.23 0.18 0.0512
(Post-ReDev)
Hydrograph Time (hrs.)
10-yr
Discharges
(cfs)
0.0
0.00
11.0
0.68
11.3
0.92
11.6
1.39
11.9
6.21
12.0
13.80
12.1
29.36
12.2
36.65
12.3
27.22
12.4
16.35
12.5
10.88
12.6
8.18
12.7
6.47
12.8
5.34
13.0
4.21
13.2
3.62
13.4
3.21
13.6
2.91
13.8
2.64
14.0
2.41
14.3
2.11
14.6
1.96
15.0
1.82
15.5
1.64
16.0
1.46
16.5
1.31
17.0
1.23
17.5
1.18
18.0
1.11
19.0
0.98
20.0
0.83
22.0
0.76
26.0
0.00
M
SCS TR-55 Post-ReDevelopment Unit
Hydrograph (ON DA A)
Worksheet 5b (Modified for Clarity): Basic watershed Data
100-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below
Subarea Tc (hrs.) Tt (hr.) la / P Am'Q (miz-in)
DA A 0.23 0.23 0.11 0.1159
(Post-ReDev)
Hydrograph Time (hrs.)
100-yr
Discharges
(cfs)
0.0
0.00
11.0
2.43
11.3
3.31
11.6
4.98
11.9
20.19
12.0
39.67
12.1
74.38
12.2
87.74
12.3
62.42
12.4
52.65
12.5
32.92
12.6
22.86
12.7
17.08
12.8
13.36
13.0
9.41
13.2
7.78
13.4
6.72
13.6
6.02
13.8
5.44
14.0
4.96
14.3
4.37
14.6
3.91
15.0
3.67
15.5
3.32
16.0
2.85
16.5
2.61
17.0
2.38
17.5
2.26
18.0
2.14
19.0
1.90
20.0
1.55
22.0
1.43
26.0
0.00
0
SCS TR-55 Post-ReDevelopment Unit
Hydrograph (ON DA A)
BasinFlow printout
INPUT:
Basin: Stockton Creek Detention Basin
5 Contour Areas
Elevation(ft) Area(sf) Computed Vol.(cy)
860.00 995.00 0.0
862.00 2342.00 120.1
864.00 3974.00 351.4
866.00 5881.00 714.1
868.00 8065.00 1228.5
Start—Elevation(ft) 860.00 Vol.(cy)
4 Outlet Structures
Outlet structure 0
Orifice
name: riser inlet
area (sf) 0.196
diameter or depth (in) 6.000
width for rect. (in) 0.000
coefficient 0.600
invert (ft) 860.000
multiple 1
discharge into riser
Outlet structure 1
Weir
name:
riser top
diameter (in)
24.000
side angle
0.000
coefficient
3.300
invert (ft)
864.170
multiple
1
discharge
into riser
transition at (ft)
0.729
orifice coef.
0.600
orifice area (sf)
3.142
Outlet structure 2
Weir
name: emergency spillway
length (ft)
40.000
side angle
0.000
coefficient
3.300
invert (ft)
866.400
multiple
1
discharge
through dam
Outlet structure 3
Culvert
name:
riser outlet
multiple
1
discharge
out of riser
D (in)
24.000
h (in)
0.000
Length (ft)
74.940
Slope
0.013
Manning's n
0.012
Inlet coeff. Ke
0.500
Equation constant set
1
Invert (ft)
859.900
4 Inflow Hydrographs
Hydrograph 0
Curve
name: 1 YR
time incr (minlhrs)
0.02
time limit (minlhrs)
30.00
file: Q:\Projects\222207
Development\CALCS\SWM\2nd
Submission\1
volume (cy)
1217.01
routed
true
time in hours
true
Hydrograph 1
Curve
- Stockton Creek Residential
YR BASIN A.txt
name: 2 YR
time incr (minlhrs) 0.02
time limit (minlhrs) 30.00
file: Q:\Projects\222207 - Stockton Creek Residential
Development\CALCS\SWM\2nd Submission\2 YR BASIN A.txt
volume (cy) 1980.77
routed true
time in hours true
Hydrograph 2
Curve
name: 10 YR
time incr (minlhrs) 0.02
time limit (minlhrs) 30.00
file: Q:\Projects\222207 - Stockton Creek Residential
Development\CALCS\SWM\2nd Submission\10 YR BASIN A.txt
volume (cy) 4835.79
routed true
time in hours true
Hydrograph 3
Curve
name: 100 YR
time incr (minlhrs) 0.02
time limit (minlhrs) 30.00
file: Q:\Projects\222207 - Stockton Creek Residential
Development\CALLS\SWM\2nd Submission\100 YR BASIN A.txt
volume (cy) 12098.06
routed true
time in hours true
OUTPUT:
Routing Method: storage -indication
Hydrograph 0
Routing Summary
of
Peaks:
1 YR
inflow
(cfs)
8.406
at
12.20
(hrs)
discharge
(cfs)
1.784
at
12.74
(hrs)
water level
(ft)
863.815
at
12.78
(hrs)
storage
(cy)
324.675
Hydrograph 1
Routing Summary
of
Peaks:
2 YR
inflow
(cfs)
14.889
at
12.20
(hrs)
discharge
(cfs)
8.473
at
12.38
(hrs)
water level
(ft)
864.631
at
12.38
(hrs)
storage
(cy)
450.762
Hydrograph 2
Routing Summary
of
Peaks:
10 YR
inflow
(cfs)
36.649
at
12.20
(hrs)
discharge
(cfs)
24.832
at
12.32
(hrs)
water level
(ft)
866.383
at
12.32
(hrs)
storage
(cy)
800.181
Hydrograph 3
Routing Summary
of
Peaks:
100 YR
inflow
(cfs)
87.736
at
12.20
(hrs)
discharge
(cfs)
85.724
at
12.20
(hrs)
water level
(ft)
866.978
at
12.20
(hrs)
storage
(cy)
945.288
Mon Jul 25 12:17:39 EDT 2022
Post-ReDevelopment DA A
Outflow Hydrograph (From
Detention Basin Routings)
Time (hrs)
Outflow (cfs)
0.0
0.00
11.0
0.00
11.3
0.00
11.6
0.00
11.9
0.09
12.0
0.41
12.1
0.92
12.2
1.32
12.3
1.57
12.4
1.69
12.5
1.74
12.6
1.77
12.7
1.78
12.8
1.78
13.0
1.77
13.2
1.75
13.4
1.72
13.6
1.68
13.8
1.64
14.0
1.60
14.3
1.52
14.6
1.43
15.0
1.30
15.5
1.13
16.0
0.94
16.5
0.76
17.0
0.64
17.5
0.57
18.0
0.53
19.0
0.46
20.0
0.40
22.0
0.30
26.0
0.02
Outflow Hydrograph (1-yr Design Storm)
1.0
Post-ReDevelopment DA A
Outflow Hydrograph (From
Detention Basin Routings)
Time (hrs)
Outflow (cfs)
0.0
0.00
11.0
0.07
11.3
0.08
11.6
0.11
11.9
0.54
12.0
0.85
12.1
1.31
12.2
1.72
12.3
5.73
12.4
8.47
12.5
6.34
12.6
4.70
12.7
3.55
12.8
2.79
13.0
2.07
13.2
1.87
13.4
1.86
13.6
1.84
13.8
1.83
14.0
1.80
14.3
1.76
14.6
1.70
15.0
1.62
15.5
1.51
16.0
1.38
16.5
1.23
17.0
1.08
17.5
0.92
18.0
0.80
19.0
0.65
20.0
0.57
22.0
0.49
26.0
0.03
27.0
0.00
9.00
8.00
7.00
6.00
5.00
4.00
3.00
2.00
1.00
0.00
-1.00
Outflow Hydrograph (2-yr Design Storm)
Post-ReDevelopment DA A
Outflow Hydrograph (From
Detention Basin Routings)
Time (hrs)
Outflow (cfs)
0.0
0.00
11.0
0.72
11.3
0.77
11.6
0.90
11.9
1.41
12.0
1.70
12.1
15.03
12.2
22.01
12.3
24.83
12.4
23.88
12.5
20.67
12.6
16.23
12.7
8.92
12.8
6.34
13.0
4.47
13.2
3.53
13.4
2.99
13.6
2.63
13.8
2.36
14.0
2.14
14.3
1.92
14.6
1.87
15.0
1.86
15.5
1.85
16.0
1.82
16.5
1.77
17.0
1.71
17.5
1.64
18.0
1.57
19.0
1.41
20.0
1.21
22.0
0.87
26.0
0.06
27.0
0.00
30.0
0.00
30.00
25.00
20.00
15.00
10.00
5.00
0.00
-5.00
Outflow Hydrograph (10-yr Design Storm)
1.0
Post-ReDevelopment DA A
Outflow Hydrograph (From
Detention Basin Routings)
Time (hrs)
Outflow (cfs)
0.0
0.00
11.0
1.84
11.3
2.24
11.6
4.10
11.9
16.14
12.0
21.61
12.1
68.70
12.2
85.72
12.3
65.56
12.4
53.56
12.5
35.95
12.6
25.18
12.7
23.58
12.8
20.98
13.0
13.43
13.2
8.22
13.4
6.97
13.6
6.22
13.8
5.59
14.0
4.98
14.3
4.24
14.6
3.67
15.0
3.31
15.5
2.95
16.0
2.51
16.5
2.24
17.0
2.05
17.5
1.95
18.0
1.88
19.0
1.86
20.0
1.83
22.0
1.70
26.0
0.25
27.0
0.01
30.0
0.00
100.00
90.00
80.00
70.00
60.00
50.00
40.00
30.00
20.00
10.00
0.00
-10.00 U
Outflow Hydrograph (10-yr Design Storm)
5.0 10.0 15.0 20.0 25.0 30.0 35.0
Virginia Runoff Reduction Method Water Quality
Calculations
(COMPLIANCE IS MET THROUGH THE BEST MANAGEMENT PRACTICE OF PURCHASING NUTRIENT CREDITS.
THE VRRM BOUNDARY IS DEFINED BY THE LIMITS OF DISTURBANCE SHOWN IN THE EROSION AND
SEDIMENT CONTROL PLAN)
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Site Information
-- ____-- _--
Post -Development Project
(Treatment Volume and Loads)
Enter
Taal Disturbed Na.(anes)
16]9
Cbe[k:
amp DesgnS onrlmfion.1]013 dam
Suds®Spe[a
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Treatment Volume and Nutrient Load
Treatment Volume and Nutrient Load
Demoeaw.w—xu..e
a1.
axat
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nova
p°n aeon axvt
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re
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Poet-DeVelopment Requirement
ftr
She Area
iP laatl Petlu[[ion 0.epuiretl Ilb/yrl
5.63
Site Results (Water Quality Compliance)
Area Checks
O.A.A
O.A.B
O.A.0
A.
D.A.E
ARMEM
FOREST/OVEN SPACE (a[)
am
O.M
0.00
i0.00
O.W
OK.
I IMPERVnUSCOVERTRENTFDIa[
0.00
0.00
0.00�M.
OWOK.
MANAGEDMRFARENIa[)
0.00
O.00
0.00
00.W
OK.
MANAGED TURF AREA TREATED (a[)
am
O.00
0.00
0.00
OK.
AREA CHECK
OK
OK.
OK.
OK.
Site Treatment VOIUMe (ffa)
19,586
Runoff Reduction Volume and TP By Drainage Area
O.A. A
D.AD
O.A. E
TOTALRUNOFF
REDUMM VOLUME ACHIEVED pF)
0
0
0
LOADAVANIBLE FOR REMOVAL (b/1)
0.00
MM0
0.000.0.00
WMI REOUCTIONAGVEVED (b/yr)
0.00
0.00
O.W
am
TP LOAD REMAINING (lb/yr)
0.00
0.00
O.W
am
NMDGEN MD REDUCTION ACHIEVED (b/yr)
am
O.W
0.00
0.00
O.W
0.00
Total Phosphorus
FINAL POST -DEVELOPMENT TP LOAD Qb/yr)
12.31
TP LOAD REDUCTION REQUIRED pb/yrl
5.63
TP WAD REDUCTIONACHIEVED (b/yr)
0.00
W LOAD REMAINING (b/,):
12.31
REMAINING TP LOAD REDUCTION REQUIRED pbM:
5.63
Total Nitrogen (For Information Purposes)
POST-DEVEMPMEM WAD (Ib/,r)jj
88.03
NU MEN LOAD REDUCTION ACHIEVED (Ib/yr)jj
0.00
REMAINING POST-DEV M MEM NrMMFN LOAD)Ib/yr)
66.03
OUTFALL PROTECTION COMPUTATIONS
OUTLET PROTECTION OUTFALL OF DETENTION BASIN
PER VESCH PLATE 3.18-1, DEPTH OF STONE (d) = 1.5 x MAX STONE DIAMETER
d>_6"
Q10= 24.29 CFS
Qdesign= 25 CFS
PER VESCH PLATE 3.18-3
d50= 0.5 FT
La= 16 FT
w1= 3*DO= 6 FT
w2= DO + La= 18 FT
FINAL DESIGN
NOTE: VDOT CLASS Al STONE HAS A MEAN
d50=O.9 FT AND EXCEEDS 0.5 FT
OUTLET PROTECTION TO INCLUDE A FILTER FABRIC UNDERLAYMENT KEYED INTO
THE EXISTING GROUND A MINIMUM OF 9" AT THE ENDS & ALONG THE PERIMETER.
EDGES OF FABRIC SHALL OVERLAP A MINIMUM OF 9". STONE TO BE VDOT CLASS Al
STONE WITH THE FOLLOWING DIMENSIONS:
La= 16 FT
w1= 6 FT
w2= 18 FT
DEPTH= 1.5 FT
DEPTH (d) >_ 1.5 X 0.9'
DEPTH (d) >_ 1.35'
OUTLET PROTECTION INTO DETENTION BASIN
PER VESCH PLATE 3.18-1, DEPTH OF STONE (d) = 1.5 x MAX STONE DIAMETER
d>_6"
Q10= 31.78 CFS
Qdesign= 32 CFS
PER VESCH PLATE 3.18-4
d50= 0.3 FT
La= 32 FT
w1= 3*DO=
w2= DO+0.4La=
FINAL DESIGN
(MIN. DISCHARGE FOR 18" DIAMETER PIPE)
6 FT
14.8 FT
NOTE: VDOT CLASS Al STONE HAS A MEAN
d50=O.9 FT AND EXCEEDS 0.5 FT
OUTLET PROTECTION TO INCLUDE A FILTER FABRIC UNDERLAYMENT KEYED INTO
THE EXISTING GROUND A MINIMUM OF 9" AT THE ENDS & ALONG THE PERIMETER.
EDGES OF FABRIC SHALL OVERLAP A MINIMUM OF 9". STONE TO BE VDOT CLASS Al
STONE WITH THE FOLLOWING DIMENSIONS:
La= 32 FT
w1= 6 FT
w2= 15 FT
DEPTH= 1.5 FT
DEPTH (d) >_ 1.5 X 0.9'
DEPTH (d) >_ 1.35'
RIPRAP OUTFALL FOR 36" CULVERT INTO EXISTING CHANNEL
Q10= 44.09 CFS
PER VESCH SPEC 3.19, PAGE III-177 (APPENDIX 3.19-a FOR'RIPRAP DESIGN IN CHANNEL')
FOR TANGENT FLOW
S= 0.056 FT/FT
PER MANNING'S EQN, DEPTH OF FLOW = 1.03' (SEE CHANNEL CALCS)
PER PLATE 3.19-3, d50= 0.75 FT
NOTE: VDOT CLASS II RIPRAP HAS A d50=1.6'
CHANNEL SIDE SLOPES = 3:1
PER PLATE 3.19-4
B=
2
d=
1.03
B/d=
1.9
z=
3
K1=
0.97
PER PLATE 3.19-5
ANGLE OF REPOSE=
PER PLATE 3.19-6
K2= 0.84
d50 X K1/K2 = d'50=
USE 21INCHES
DEPTH = 2 X d50 = 42"
390
18 IN X 0.97/0.84= 20.79 IN
FINAL DESIGN FOR RIPRAP OUTFALL CHANNEL
OUTLET PROTECTION TO INCLUDE A FILTER FABRIC UNDERLAYMENT KEYED INTO
THE EXISTING GROUND A MINIMUM OF 9" AT THE ENDS & ALONG THE PERIMETER.
EDGES OF FABRIC SHALL OVERLAP A MINIMUM OF 9". STONE TO BE VDOT CLASS II
STONE AT A DEPTH OF 42 INCHES. RIPRAP CHANNEL TO EXTEND 30 FEET INTO
EXISTING CHANNEL AFTER CULVERT OUTLET.
OUTLET PROTECTION TEMPORARY PIPE
PER VESCH PLATE 3.18-1, DEPTH OF STONE (d) = 1.5 x MAX STONE DIAMETER
Q10= 0.65 CFS
Qdesign= 6.5 CFS
PER VESCH PLATE 3.18-3
d50= 0.5 FT
(MIN.d50)
La= 9 FT
w1= 3*DO=
w2= DO + La=
FINAL DESIGN
d>_6"
(MIN. DISCHARGE FOR 15" PIPE PER PLATE 3.18-1)
3.75 FT
10.25 FT
NOTE: VDOT CLASS Al STONE HAS A MEAN
d50=O.9 FT AND EXCEEDS 0.5 FT
OUTLET PROTECTION TO INCLUDE A FILTER FABRIC UNDERLAYMENT KEYED INTO
THE EXISTING GROUND A MINIMUM OF 9" AT THE ENDS & ALONG THE PERIMETER.
EDGES OF FABRIC SHALL OVERLAP A MINIMUM OF 9". STONE TO BE VDOT CLASS Al
STONE WITH THE FOLLOWING DIMENSIONS:
La= 9 FT
w1= 3.75 FT
w2= 10.25 FT
DEPTH= 1.5 FT
DEPTH (d) >_ 1.5 X 0.9'
DEPTH (d) >_ 1.35'