HomeMy WebLinkAboutWPO201900027 Calculations 2021-02-03PLEASANT GREEN- CONNECTOR ROAD
STORMWATER MANAGEMENT CALCULATIONS PACKET
Date of Calculations
OCTOBER 2, 2020
Revised on
NOVEMBER 17, 2020
Revised on
JANUARY 27, 2021
I:1C1W_1Cf4III -i'il
COLLINS ENGINEERING
200 GARRETT STREET, SUITE K
CHARLOTTESVILLE, VA 22902
434.293.3719 PH
434.293.2813 FX
www.collins-engineering.com
Summary of January 2711 Revisions:
1. The cover sheet was updated to provide a seal and a new revision date.
2. The biofilter, which previously was proposed for water quality compliance, was removed. The
biofilter is no longer needed since the Phases II & III plan (WPO 202000053) provides an
excess water quality credit that can be applied to this project. As a result, the approval of
Phases II & III's SWM plan (WPO 202000053) will be required prior to this plan's approval.
3. SCS TR-55's Worksheets 2-4 and the associated hydrographs were tweaked to account for the
removal of the biofilter. Also, the previously shown routings were removed and were
replaced with storm sewer computations showing the 10-year design storm is contained
within the system without an overtopping. The plan's method for meeting minimum channel
and flood protection compliances has not changed.
SCS TR-55 Calculations
lei
Soils Table
(Source: NRCS Web Soil Survey Online Database)
Albemarle County, Virginia (VA003)
Map
Unit
Map Unit Name
percent of
Symbol
cen
01
7B
Braddock loam,
13.0%
2 to 7 percent
slopes
17
Craigsville loam,
51.9%
0 to 2 percent
slopes,
frequently
flooded
37D3
Hayesville clay
35.1%
loam, 15 to 25
percent slopes,
severely eroded
Totals for Area of
100.00/0
Interest
The NRCS web soil survey defines this development's soils as predominantly having a hydrologic group type A.
Precipitation Data
(Source: NOAA's National Weather Service, Hydrometerorological Design Studies Center, Atlas 14
Point Precipitation Frequency Estimates)
Map
Terrain
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J"d,
POINT PRECIPITATION FREQUENCY (PF) ESTIMATES
WITH 90% CONFIDENCE INTERVALS AND SUPPLEMENTARY INFORMATION
NOAA Atlas 14, Volume 2, Version 3
I PDS-based precipitation frequency estimates with 90 % confidence intervals (in inches)' I
3.08 3.72 C74 5.59 6.84 7.97 9.09 10A 12.3 140
24.Ir (2.77-344) 1 (3.354.16) 1 (4.255.30) 1 (5.005.24) 1 (6.08-7.62) 1 (6.9".80) 1 (7.90.10.1) 1 (8.W11.5) 1 (10.5-13.7) 1 (11.7-15.6)
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U.S. Department of Agriculture
Natural Resources Conservation Service
TR 55 Worksheet 3: Time of Concentration (T j or Travel Time (TJ
Project: Pleasant Green- Connector Rd.
Location: Orchard Dr. Connection
Check One: Present X Developed X
Check One: T, X T,
Sheet Flow: (Applicable to T, only)
Designed By: FGM, PE
Checked By: SRC, PE
Through subarea n/a
Segment ID:
1 Surface description (Table 3-1)
2 Manning's roughness coeff., n (Table 3-1)
3 Flow length, L (total L < 100) (ft)
4 Two-year 24-hour rainfall, Pz (in.)
5 Land slope, s (ft/ft)
6 Compute T, _ [0.007(n*L)"] / P2" SIA
Shallow Concentrated Flow:
7 Surface description (paved or unpaved)
8 Flow Length, L (ft)
9 Watercourse slope, s (ft/ft)
10 Average velocity, V (Figure 3-1) (ft/s)
11 Tt= L / 3600*V
Channel Flow:
12 Cross sectional flow area, a (ft)
13 Wetted perimeter, Pw (ft)
14 Hydraulic radius, r= a/Pw (ft)
15 Channel Slope, s (ft/ft)
16 Manning's Roughness Coeff, n
17 V= [ 1.49r2/3s05 ] / n
18 Flow length, L (ft)
19 T,= L / 3600*V
20 Watershed orsubareaT,orT,
(Add Tt in steps 6, 11 and 19)
Note: The shoretest SCS Tc is 0.10 hrs.
FL-ENG-21A
06/04
Date: 1/27/2021
Date: 1/27/2021
DAA
DAA
(Pre-Dev.)
(Post-Dev.)
Woods- Light
Dense
Underbrush
Grass
0.4
0.24
100
30
3.72
3.72
0.180
0.067
0.14
0.05
Unpaved
Paved
140
10
0.04
0.02
3.2
2.9
0.01
0.00
o
LL
E
+
ON
c
C
of
ul
�
u
Y
o
m
3
c
N
N
0.02
0.15 1 0.10
U.S. Department of Agriculture
Natural Resources Conservation Service
TR 55 Worksheet 4: Graphical Peak Discharge Method
Project: Pleasant Green- Connector Rd. Designed By: FGM, PE Date: 11/17/2020
Location: Orchard Dr. Connection Checked By: SRC, PE Date: 11/17/2020
Check One: Present X Developed X
1. Data
Drainage Area
Description
Drainage Area
Description
Drainage Area
Description
DA A
(Pre-Dev.)
DA A
(Post-Dev.)
Drainage Area (Am) in mileS2 =
0.0014
0.0014
Runoff curve number CN=
55
90
Time of concentration (Tc)=
0.15
0.10
Rainfall distribution type=
II
II
Pond and swamp areas spread
throughout the watershed=
0
0
2. Frequency -years
1 2
10
1
2
10
3. Rainfall, P (24 hour)- inches
3.08 3.72
5.59
3.08
3.72
5.59
4. Initial Abstraction, la- inches
1.64 1.64
1.64
0.21
0.21
0.21
5. Compute la/P
0.53 0.44
0.29
0.07
0.06
0.04
6. Unit peak discharge, Qu- csm/in
425 600
825
1000
1000
1000
7. Runoff, Q from Worksheet 2- inches
0.22 0.42
1.29
2.10
2.70
4.50
8. Pond and Swamp adjustment factor, Fp
1 1 1
1
1
1 1
1
1
9. Peak Discharge, Qp- cfs
where Qp=Qu Am Q Fp
See SCS Unit
I Hydrographs
See SCS Unit
Hydrographs
WATERSHED SUMMARY
CN ac. cfs cfs cfs
FA (Pre-Dev.) 55 0.92 0.17 0.33 1.73
A (Post-Dev.) 90 0.92 3.05 3.92 6.53
Channel and Flood Protection Computations
9 VAC 25-870-66
Section B: Channel Protection
"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.a.
"The manmade stormwater conveyance system shall convey the postdevelopment peak flow
rate from the two-year 24-hour storm event without causing erosion of the system."
Note, the 2-year 24-hour storm event is not erosive on concrete pipe and riprap.
Section B.4 Limits of Analysis
"stormwater conveyance systems shall be analyzed for compliance with channel protection
criteria to a point where either.." a. or b. are met
Section B.4.a.
"Based on land area, the site's contributing drainage area is less than or equal to 1.0% of the
total watershed area;"
Note, the analysis terminates at the point of analysis (i.e. the location in Powells Creek where
manmade riprap improvements are proposed).
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.a.:
The point of discharge "confines the postdevelopment peak flow rate from the 10-year 24-
hour storm event within the stormwater conveyance system to avoid the localized flooding."
Note, the 10-year 24-hour storm event is confimed within the storm sewer and riprap outlet
protection located within Powells Creek.
Section C.3.c Limits of Analysis
The flood protection analysis terminates at the site outfall because, "the stormwater
conveyance system enters a mapped floodplain."
Pre -Development Inflow Hydrographs
(Pre-Dev. 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 (mi2-in)
DAA (Pre-Dev.) 0.15 0.15 0.53 0.000311
Hydrograph Time 1-yr Discharges
(hrs.)
(cfs)
0.0
0.00
11.0
0.00
11.3
0.00
11.6
0.00
11.9
0.00
12.0
0.02
12.1
0.17
12.2
0.12
12.3
0.06
12.4
0.05
12.5
0.05
12.6
0.04
12.7
0.04
12.8
0.03
13.0
0.03
13.2
0.03
13.4
0.03
13.6
0.02
13.8
0.02
14.0
0.02
14.3
0.02
14.6
0.02
15.0
0.02
15.5
0.02
16.0
0.01
16.5
0.01
17.0
0.01
17.5
0.01
18.0
0.01
19.0
0.01
20.0
0.01
22.0
0.01
26.0
0.00
0.18
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
-0.02
SCS TR-55 Pre -Development Unit
Hydrograph (DA A)
0.0
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 (mi2-in)
DAA (Pre-Dev.) 0.15 0.15 0.44 0.001
Hydrograph Time 2-yr Discharges
(hrs.)
(cfs)
0.0
0.00
11.0
0.00
11.3
0.00
11.6
0.00
11.9
0.00
12.0
0.04
12.1
0.33
12.2
0.23
12.3
0.12
12.4
0.10
12.5
0.09
12.6
0.08
12.7
0.07
12.8
0.07
13.0
0.06
13.2
0.05
13.4
0.05
13.6
0.05
13.8
0.04
14.0
0.04
14.3
0.04
14.6
0.04
15.0
0.03
15.5
0.03
16.0
0.03
16.5
0.03
17.0
0.03
17.5
0.02
18.0
0.02
19.0
0.02
20.0
0.02
22.0
0.02
26.0
0.00
0.35 F-
SCS TR-55 Pre -Development Unit
Hydrograph (DA A)
Worksheet 51b (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 (mil -in)
DAA (Pre-Dev.) 0.15 0.15 0.29 0.0019
Hydrograph Time 10-yr Discharges
(hrs.)
(cfs)
0.0
0.00
11.0
0.00
11.3
0.00
11.6
0.00
11.9
0.29
12.0
1.05
12.1
1.73
12.2
0.97
12.3
0.40
12.4
0.32
12.5
0.28
12.6
0.23
12.7
0.20
12.8
0.18
13.0
0.16
13.2
0.14
13.4
0.13
13.6
0.12
13.8
0.11
14.0
0.10
14.3
0.09
14.6
0.09
15.0
0.08
15.5
0.07
16.0
0.06
16.5
0.06
17.0
0.06
17.5
0.05
18.0
0.05
19.0
0.04
20.0
0.04
22.0
0.04
26.0
0.00
.00 1IL
.ao
1.60
1.40
1.20
1.00
0.90
0.60
0.40
0.20
0.00
0
SCS TR-55 Pre -Development Unit
Hydrograph (DA A)
Post -Development Inflow Hydrographs
(Post-Dev. 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 (mi2-in)
DA A (Post-Dev.) 0.10 0.10 0.07 0.0030
Hydrograph Time 1-yr Discharges
(hrs.)
(cfs)
0.0
0.00
11.0
0.07
11.3
0.10
11.6
0.16
11.9
1.01
12.0
1.95
12.1
3.05
12.2
1.88
12.3
0.65
12.4
0.44
12.5
0.37
12.6
0.31
12.7
0.26
12.8
0.23
13.0
0.20
13.2
0.17
13.4
0.15
13.6
0.14
13.8
0.13
14.0
0.11
14.3
0.10
14.6
0.10
15.0
0.09
15.5
0.08
16.0
0.07
16.5
0.06
17.0
0.06
17.5
0.06
18.0
0.05
19.0
0.05
20.0
0.04
22.0
0.04
26.0
0.00
SCS TR-55 Post -Development Unit
Hydrograph (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 (mi2-in)
DA A (Post-Dev.) 0.10 0.10 0.06 0.0039
Hydrograph Time 2-yr Discharges
(hrs.)
(cfs)
0.0
0.00
11.0
0.09
11.3
0.13
11.6
0.21
11.9
1.30
12.0
2.51
12.1
3.92
12.2
2.42
12.3
0.84
12.4
0.57
12.5
0.48
12.6
0.40
12.7
0.33
12.8
0.29
13.0
0.26
13.2
0.22
13.4
0.20
13.6
0.18
13.8
0.16
14.0
0.15
14.3
0.13
14.6
0.12
15.0
0.11
15.5
0.10
16.0
0.09
16.5
0.08
17.0
0.08
17.5
0.07
18.0
0.07
19.0
0.06
20.0
0.05
22.0
0.05
26.0
0.00
4.50
4.00
3.50
3.00
2.50
2.00
1.50
1.00
0.50
0.00
0.0
SCS TR-55 Post -Development Unit
Hydrograph (DA A)
5.0 10.0 15.0 20.0 25.0 30.0
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 (mil -in)
DA A (Post-Dev.) 0.10 0.10 0.04 0.0065
Hydrograph Time 10-yr Discharges
(hrs.)
(cfs)
0.0
0.00
11.0
0.16
11.3
0.22
11.6
0.34
11.9
2.16
12.0
4.18
12.1
6.53
12.2
4.03
12.3
1.40
12.4
0.95
12.5
0.80
12.6
0.67
12.7
0.56
12.8
0.49
13.0
0.43
13.2
0.37
13.4
0.33
13.6
0.30
13.8
0.27
14.0
0.25
14.3
0.22
14.6
0.21
15.0
0.19
15.5
0.17
16.0
0.15
16.5
0.14
17.0
0.13
17.5
0.12
18.0
0.12
19.0
0.10
20.0
0.08
22.0
0.08
26.0
0.00
7.00
6.00
5.00
4.00
3.00
2.00
1.00
0.00
0.0
SCS TR-55 Post -Development Unit
Hydrograph (DA A)
5.0 10.0 15.0 20.0 25.0 30.0
Post -Development Storm Sewer Calculations
(Confirms confinement of Post -Development Subarea A's 10-yr Storm)
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Riprap Lined Outlet Protection Calculations
Below the Triple Box Culvert
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Complex Channnel
Input:
Slope 0.008
Flow (given) 820.000
line x y n
0 218.000 691.100
1 220.000 690.900
2 225.000 687.100
3 260.000 687.100
4 270.000 690.000
Output:
Depth 2.608
(y) ( 689.708)
Channel bed segment output
0.030 (first n value not used)
0.030
0.030
0.030
0.030
line
Q
V
A
P
1
0.00
0.00
0.00
0.00
2
19.68
4.40
4.47
4.31
3
741.87
8.13
91.28
35.00
4
58.45
4.98
11.73
9.36
Fri Sep 25 14:07:58 EDT 2020
file: ///P/...lanNSMP%20Plan-%20Connector%20Road/Calculations/SWM1s[%20Submittal/Culvert%20Crossing-%20Riprap%20Design.tKt[9/25/2020 2:14:27 PMl
HEC RAS Analysis for the Pleasant Green Proposed Crossing
(i.e. The Proposed Connector Road Crossing)
HEC RAS Analysis
for
Pleasant Green Proposed Crossing
Crozet, VA
Prepared for Collins Engineering
April 1, 2019
Revised: June 6, 2019
BACKGROUND
The proposed project is located along the northeast side of Powells Creek between Jarmans Gap
Road and Cling Lane in Crozet, Virginia. The proposed development, known as Pleasant Green,
includes an entrance road that crosses the regulatory floodplain (FEMA Zone AE) of Powells
Creek from Orchard Drive in the vicinity of FEMA cross section "G" (FEMA Map: 51003CO229D).
A hydraulic analysis was conducted to assess the impacts of this proposed stream crossing on
the Base Flood Elevations upstream of the crossing. A prior hydraulic analysis of this reach was
completed in May 2017 by Dominion Engineering for the then proposed West Glen Subdivision -
which included a similar crossing in the vicinity of FEMA cross section "I".
HYDROLOGY
Peak flows for Powells Creek have been estimated by FEMA and are presented within Table 3 of
Flood Insurance Study #51003CV000C, for Albemarle County, VA. No further hydrologic
calculations were conducted for this analysis.
HYDRAULICS
A HEC-RAS (version 5.0.6) hydraulic model was developed, for both existing and proposed
conditions, to assess impacts to the (100-year) base flood elevations and floodplain extents for
Powells Creek immediately upstream of the proposed Pleasant Green crossing. Dominion
Engineering's previous existing condition ("effective") model was used as the basis for this new
model. The following model components were used in this analysis.
Cross Sections
Aterrain model built with updated topographic survey data provided by Dominion
Engineering (2017) was used to provide elevation data for the HEC RAS model. FEMA cross
section data was revised accordingly for cross sections F — M. For this analysis, cross section
G was replaced with 6 new sections (G1, G2, G3, G4, G5, G6) to adequately model the
proposed crossing. Manning's Roughness (n) values were set at 0.08 within the channel and
0.06 for overbank conditions, as referenced in Table 4 of FEMA Flood Insurance Study
#51003CV000C.
Culverts
Three (3) 8'H x 10'W concrete box culverts were modeled for proposed conditions. Culverts
were countersunk 6-8" and modeled with a natural bottom and roughness value of 0.03.
Channel roughness values immediately upstream and downstream of the culverts were also
set at 0.03 to account for proposed inlet and outlet protection. Culverts were modeled as
Inlet Controlled. Ineffective flow areas were set upstream and downstream of the proposed
crossing, in accordance with HEC RAS guidance.
Flows
A steady flow model using a subcritical flow regime was used for this analysis. Flow data
was unchanged from Dominion Engineering's model. Flow values are as follows:
Reach
RS
10 YR
50 YR
100 YR
FLOODWAY
500 YR
POWELLS CREEK
4182.66
750 1200
1370 1370
2010
2040
2050
POWELLS CREEK
3384.41
770 1230
140D 1400
POWELLS CREEK
2959.02
780 1240
1410 1410
1430 1430
1450 1450
1460 1460
POWELLS CREEK
2559.86
790 1260
2070
POWELLS CREEK
1979.71
800 1280
2090
POWELLS CREEK
1651.13
810 1290
2100
POWELLS CREEK
908.45
820 1320
840 1340
11480
1480
2130
POWELLS CREEK
202.38
11510
11510
2160
RESULTS
The results of this model estimate a maximum rise of 2.59' in 100-year flood elevations
immediately upstream of the proposed crossing. The model also indicates a small rise
downstream of the proposed crossing — due to a modeled hydraulic jump as flows rapidly
decrease in velocity from geometry expansion and high downstream channel roughness (0.08).
Impacts to the extents of the 100-year floodplain are displayed on the design plans. HEC RAS
output table, flood profiles, and cross sections have been provided in Appendix A of this memo.
APPENDIX A
Cross Section
River Sta
Profile
Plan
Q Total
W.S. Elev
W.S.E. Rise
Vel Chnl
Top Width
(cfs)
(ft)
(ft)
NO
(ft)
m
4182.66
100 YR
Proposed
1370
769.02
0.00
7.76
166.87
m
4182.66
100 YR
Existing
1370
769.02
7.76
166.87
L4
3932.07
100 YR
Proposed
1370
765.97
0.00
2.05
206.54
L4
3932.07
100 YR
Existing
1370
765.97
2.05
206.54
L3
3891.62
100 YR
Proposed
1370
765.68
0.00
4.57
166.44
L3
3891.62
100 YR
Existing
1370
765.68
4.57
166.44
EX. CULVERT - CLING
LANE
3861.37
Culvert
L2
3831.12
100 YR
Proposed
1370
761.23
0.00
7.69
136.93
L2
3831.12
100 YR
Existing
1370
761.23
7.69
136.93
Ll
3791.09
100 YR
Proposed
1370
759.93
0.00
5.7
164.91
Ll
3791.09
100 YR
Existing
1370
759.93
5.7
164.89
L
3384.41
100 YR
Proposed
1400
747.97
0.00
7.96
118.84
L
3384.41
100 YR
Existing
1400
747.97
7.95
118.84
K
2959.02
100 YR
Proposedl
1410
737.63
1 0.00
6.31
1 119.09
K
2959.02
100 YR
Existing
1410
737.63
6.31
119.08
1
2559.86
100 YR
Proposed
1430
727.79
0.00
7.35
153.27
1
2559.86
100 YR
Existing
1430
727.79
7.35
153.27
1
1979.71
100 YR
Proposed
1450
714.42
0.00
6.5
102.6
1
1979.71
100 YR
Existing
1450
714.42
6.5
102.6
H
1651.13
100 YR
Proposed
1460
708.4
0.00
5.92
130.07
H
1651.13
100 YR
Existing
1460
708.4
5.92
130.08
G6
1159.5
100 YR
Proposed
1460
695.93
0.00
7.26
194.41
G6
1159.5
100 YR
Existing
1460
695.93
7.26
194.41
G5
1057.41
100 YR
I Proposedl
1460
694.87
1 1.61
6.07
1 315.68
G5
1057.41
100 YR
Existing
1460
693.26
4.52
229.04
G4
1021.3
100 YR
Proposed
1460
694.82
2.59
4.92
310.2
G4
1021.3
100 YR
Existing
1460
692.23
4.56
189.38
PROPOSED CROSSING
966.8
Culvert
G3
908.45
100 YR
Proposed
1480
690.91
0.25
10.12
1 229.3
G3
908.45
100 YR
Existing
1480
690.66
2.92
219.1
G2
835.86
100 YR
Proposed
1480
690.45
0.61
5.18
251.09
G2
835.86
100 YR
Existing
1480
689.84
4.23
238.2
Gl
562.24
100 YR
Proposed
1480
683.57
0.00
6.62
225.94
Gl
562.24
1 100 YR
Existing
1480
683.57
6.67
226.08
F
202.38
100 YR
I Proposedl
1510
1 678.4
1 0.00
1 4.65
1 154.37
F
202.38
1 100YR
I Existing
1 1510
1 678.4
1
1 4.65
1 154.37
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Water Quality Calculations for the Proposed Plan, Using the DEQ
Virginia Runoff Reduction Method for New Developments
NOTEWORTHY WATER QUALITY ITEMS:
1. The VRRM water quality boundary is defined by the ESC boundary for this plan's limits of disturbance,
which is 1.99 acres. In other words, the following VRRM water quality calculations are for this plan's
disturbed areas and quantify a phosphorous removal rate associated with the construction of the
Connector Road.
2. The water quality requirements for this plan are met with the Pleasant Green development. The
phosphorous removal rates provided in the Phase I plan (WPO 201900003) and the Phases II and III
plan (WPO 202000053) exceed the overall minimum required phosphorous removal rate for all of
Pleasant Green. This surplus in phosphorous removal credit is applied to this plan / portion of the
Pleasant Green development.
11
Overall Water Quality Calculations for the Pleasant Green Development,
Using the DEQ Virginia Runoff Reduction Method for New Developments
NOTEWORTHY WATER QUALITY ITEMS:
1. Water quality compliance is met for the overall Pleasant Green Development. The phosphorous
removal rates provided in the Phase I plan (WPO 201900003) and the Phases II & III Plan (WPO
202000053) exceed the overall minimum required phosphorous removal rate for all of Pleasant Green,
inclusive of this plan's connector road. Those two Pleasant Green WPO plans' phosphorous removal
rate credits are applied to this plan's portion of the Pleasant Green Development. The following
calculations show the overall Pleasant Green's water quality analysis, which includes Phases I, II, III
and the Connector Road (this plan).
2. The VRRM water quality boundary is defined by the overall ESC boundary for the Pleasant Green's
limits of disturbance (i.e. all disturbed areas associated with the Pleasant Green development are
reflected in the following VRRM calculations to ensure compliance is met).
3. Following the above mentioned VRRM calculations, a Pleasant Green Water Quality Master Plan
summary has been provided to illustrate the development's overall compliance, as well as to
demonstrate how 75% of the required phosphorous removal rate is treated onsite. Behind this in the
report, is another VRRM computation that shows the phosphorous removal rate credit associated with
Phases II and III's SWM open space easement.
11
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Q
Analysis of Temporary ESC Stream Diversion
(Note: Design warrants a Type C Diversion)
ESC Temporary Stream Diversion
Complex Channnel- Analysis for Temporary USC Diversion
Input:
Slope 0.021
Flow (given) 820.000
line
x
y
n
0
0.000
5.500
0.050 (first n value not used)
1
11.000
0.000
0.050
2
17.000
0.000
0.050
3
28.000
5.500
0.050
Output:
Depth 5.223
(Y) ( 5.223)
Channel bed segment output:
line
Q
V
A
P
1
206.84
7.58
27.28
11.68
2
406.31
12.97
31.34
6.00
3
206.84
7.58
27.28
11.68
Wed Sep 30 13:26:08 EDT 2020
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