HomeMy WebLinkAboutWPO201800080 Calculations Stormwater Management PlanBROOKHILL FINAL STORMWATER
MANAGEMENT CALCULATIONS PACKET
(Block 8B)
Date of Calculations
OCTOBER 24, 2018
Revised on
JAN UARY 18, 2019
Revised on
AUGUST 5, 2019
RECEIVED
COMMUNITY
DEVELOPMENT
PREPARED BY: °'�' �� ;,Y"nt
R v
COLLINS
200 GARRETT STREET, SUITE K
CHARLOTTESVILLE, VA 22902
434.293.3719 PH
434.293.2813 FX
www.collins-engineering.com
Off,
rr'
COLLlt,c
"4 .s
444/
Supplemental Stormwater Quality Narrative for Brookhill's Block 8B:
1. Block 8B requires 0.83 Ibs/yr of phosphorous to be purchased (6.74 Ibs/yr -5.91 Ibs/yr =0.83 Ibs/yr).
Block 813's required removal rate is 6.74 Ibs/yr and the proposed wet pond removes 5.91 Ibs/yr. This is
depicted on the Block 8B SWM plan and narrative shown on sheet 6.
2. For Brookhill's Overall compliance, 1.53 Ibs/yr of phosphorous is required to be purchased (0.83 Ibs/yr
+ 0.67 Ibs/yr + 0.03 Ibs/yr). This is shown on the 'Overall' Brookhill sheet 9 compliance sheet, note #2.
This total amount is required because (in addition to the Block 8B removal rate):
A. An additional 0.67 Ibs/yr nutrient credit needs to be purchased for the removal of the
downstream level spreader (I-S-10), and
B. An additional 0.03 Ibs/yr nutrient credit is required per a deficit in the WPO 201800013 plans.
3. In conclusion, 1.53 Ibs/yr of phosphorous is required to be purchased.
Stormwater_Manaciement Narrativ
Overview:
This project is part of the Brookhill development, and stormwater treatment is provided to
mitigate the impacts from the proposed improvements. The stormwater management plan
complies with part IIB SWM requirements.
Water Quality Summary
The stormwater quality requirements for this development are met through the use of the best
management practices of a level II wet pond and the purchasing of nutrient credits. The proposed
development requires an overall phosphorous removal rate of 6.74 Ibs/yr. and the level II wet
pond provides a phosphorous removal rate of 5.91 Ibs/yr. The remaining balance of 0.83 Ibs/yr.
will be mitigated through the purchasing of nutrient credits.
In accordance with County Engineering direction, the impervious areas from Stella Lane are
assumed to be zero in the pre -development analyses for both water quality and quantity, but are
accounted for in the post -development analyses.
Also in accordance with County Engineering direction, the VRRM water quality computations take
Stella Lane's areas into consideration. (Please note, the VRRM 'site' land cover is consequently
defined by the limits of disturbance plus this portion of Stella Lane.) Please also note, the offsite
areas not being developed in the vicinity of the historic home are not part of the VRRM 'site'
areas. This is a state-wide industry standard, as these areas are not part of this project.
Additionally, to ensure a conservative / compliant plan, the offsite areas not being developed
near the historic home are omitted from the 'DA A' water quality calculations. This is a
conservative design because even though the wet pond treats the upland offsite areas in reality,
it would falsely generate a higher phosphorous removal credit in the calculations since it would
take credit for areas in its watershed that are outside the scope of this project. These offsite
areas were accounted for in the water quantity analyses.
Water Quantity Summary
Subareas A & B and subarea C meet minimum stormwater quantity requirements.
The proposed development, which is mostly encompassed within subareas A & B, outfalls
immediately upland of an existing channel. A proposed level II wet pond (subarea A) was
conservatively designed assuming the proposed underground detention system (subarea B) is
clogged. This conservative design provides a factor of safety & further cements the plan's
compliance. Channel and flood protection requirements set forth in 9 VAC 25-870-66 are met.
Please see the following stormwater management calculations for additional details.
The modifications to the storm sewer structures along Stella Lane (subarea C) were also analyzed
for 9 VAC 25-870-66 stormwater quantity compliance. In accordance with the approved WPO
201800051 plans, Stella Lane's peak post -development flows (Q developed) at point of interest-
11, or POI-11, are substantially below the maximum allowable flows (Q allowed). The approved
WPO 201800051 calculations show an over detention for POI-11, which allows for minor
additional runoff (subarea C) to outfall to it without negating the approved MS-19 & energy
balance calculations. The minor increase in runoff to POI-11 from this plan / subarea C, when
added with the approved WPO 201800051 post -development flows (Q developed), continues to
remain below the approved maximum allowed (Q allowed) for POI-11. Please see the following
calculations & WPO 201800051 for further details.
SCS TR-55 Calculations
Sods Mapping (Source: NRCS Web Soil Survey Online Database)
Soils Table (Source: NRCS Web Soil Survey Online Database)
Albemarle County, Virqinia (VA003)
Albemarle County, Virginia
(VA003)
Map Unit Map Unit Name
percent of
Symbol
AOI
27B Elioak loam, 2
8.90/0
to 7 percent
slopes
27C Elioak loam, 7
32.9%
to 15 percent
slopes
27D Elioak loam,
11.4%
15to25
percent slopes
39D Hazel loam, 15
45.81)/o
to 25 percent
slopes
Totals for Area of
100.00/0
Interest
Note: The soils' properties witin this development are predominantly composed of hydrologic group
type B soils.
Precipitation Data
(Source: NOAA's National Weather Service, Hydrometerorological Design Studies Center, Atlas 14
Point Precipitation Frequency Estimates)
Terrain
yr
os
i+
S
A.
'Fii1�u i4
e
�4
t"+
1
4�at,t"r
4,
fi�rxd� Gr�alnrt4 7ir1
{i
3
0.4km
Carrsbrook
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)'
6uratian
Average recurrence interval (years)
��� 10 25 50 100 200 500 E(11.7-15.5)
3.00 3.63 4.64 5.49 6.74 7.81 8.99 10.3 12.3(269-3.38)
(3.26-409) (4.15-5.21) (489-6.15) (5.97-753) (6.87-8.71) (785-10.0) (8.89-11.4) (10.4-136)
U.S. Department of Agriculture
Natural Resources Conservation Service
Project: Brookhill Development
Location: Block 8B
Check One: Present X Developed
1. Runoff curve Number (CN)
FL-ENG-21A
06/04
TR 55 Worksheet 2: Runoff Curve Number and Runoff
Designed By: FGM, PE Date: 1/18/2019
Checked By: SRC, PE Date: 1/18/2019
Drainage Area
8
Soil name and
Cover description
Area
Product of CN
CN (weighted) _
Calculated
Description
P
hydrologic group
(Cover type, treatment, and hydrologic condition; percent
CN
(Acres)
Area
total product/
Value
(Appendix A)
impervious; unconnected/ connected impervious area ratio)
x
total area
S'
DA A
Impervious Areas
98
0.00
0.0
(Pre-Dev.)
B
Woods in Good Condition
55
2.48
136.4
58.6
7.07
Lawns in Good Condition (75%+ Groundcover)
61
3.65
222.7
DA B
Impervious Areas
98
0.00
0.0
(Pre-Dev.)
B
Woods in Good Condition
55
1.55
85.3
56.7
7.64
Lawns in Good Condition (75%+Groundcover)
61
0.61
37.2
DAA
Impervious Areas
98
3.09
302.9
(Post-Dev.)
B
Woods in Good Condition
55
1.12
61.6
76.4
3.08
Lawns in Good Condition (75%+ Groundcover)
61
2.76
168.3
DA B
Impervious Areas
98
0.63
61.3
(Post-Dev.)
B
Woods in Good Condition
55
0.26
14.3
77.3
2.93
Lawns in Good Condition (75%+ Groundcover)
61
0.44
26.5
DA C
Impervious Areas
98
0.22
21.9
(Post-Dev.)
B
Woods in Good Condition
55
0.00
0.0
81.7
2.24
Lawns in Good Condition (75%+Groundcover)
61
0.18
10.7
2. Runoff
1-Year Storm
2-Year Storm
10-Year Storm
Drainage Area Description
Frequency -years
1
2
10
n/a
Rainfall, P (24 hour)- inches
3.00
3.63
5.49
n/a
Runoff, Q-inches
0.29
0.53
1.49
DA A (Pre-Dev)
Runoff, Q-inches
0.24
0.45
1.35
DA B(Pre-Dev)
Runoff, Q- inches
1.04
1.49
2.99
DA A (Post-Dev)
Runoff, Q- inches
1.09
1.55
3.07
DA B (Post-Dev.)
Runoff, Q- inches
1.36
1.87
3.49
IDA C (Post-Dev)
U.S. Department of Agriculture
Natural Resources Conservation Service
TR 55 Worksheet 3: Time of Concentration (TJ or Travel Time (Tt)
Project: Brookhill Development
Location: Block 8B
Check One: Present X Developed X
Check One: T, X Tt
Segment ID:
Sheet Flow: (Applicable to Tc only)
Designed By: FGM, PE
Checked By: SRC, PE
Through subarea n/a
FL-ENG-21A
06/04
Date: 1/18/2019
Date: 1/18/2019
DA A
DA B
DA A
DA B
DA C
(Pre-Dev.)
(Pre-Dev.)
(Post-Dev.)
(Post-Dev.)
(Post-Dev.)
1 Surface description (Table 3-1)
Dense Grass
Dense Grass
Dense Grass
Dense Grass
2 Manning's roughness coeff., n (Table 3-1
0.24
0.24
0.24
0.24
3 Flow length, L (total L < 100) (ft)
100
100
100
100
4 Two-year 24-hour rainfall, PZ (in.)
3.6
3.6
3.6
3.6
5 Land slope, s (ft/ft)
0.05
0.07
0.05
0.05
6 Compute Tt = [0.007(n*L)o.8] / P20.5 SOA
0.15
0.14
0.15
0.15
Shallow Concentrated Flow:
7 Surface description (paved or unpaved)
Unpaved
Unpaved
Unpaved
Unpaved
8 Flow Length, L (ft)
170
320
150
150
9 Watercourse slope, s (ft/ft)
0.112
0.169
0.087
0.160
10 Average velocity, V (Figure 3-1) (ft/s)
5.5
6.8
4.8
6.5
11 Tt = L / 3600*V
0.01
0.01
0.01
0.01
Channel Flow:
12 Cross sectional flow area, a (ft)
a
3
t
Y
a
0
4-
13 Wetted perimeter, P. (ft)
�
$
y
$
a
\
14 Hydraulic radius, r = a/PW (ft)
U Ln
66 $
15 Channel Slope, s (ft/ft)
s @�
u %
I
16 Manning's Roughness Coeff, n
w 3
0
0 3
17 V= [ 1.49r'/3s0.5 ] / n
0
0
0
0 �
18 Flow length, L (ft)
in
-0
19 Tt= L / 3600*V
0.02
0.02
0.00
20 Watershed or subarea Tc or Tt
(Add Tt in steps 6, 11 and 19)
0.18
0.15 0.18
0.16 0.10
U.S. Department of Agriculture
Natural Resources Conservation Service
Project: Brookhill Development
Location: Block 8B
Check One: Present X Developed X
TR 55 Worksheet 4: Graphical Peak Discharge Method
Designed By: FGM, PE
Checked By: SRC, PE
FL-ENG-21C
06/04
Date: 8/5/2019
Date: 8/5/2019
1. Data
Drainage Area
Description
Drainage Area
Description
Drainage Area
Description
Drainage Area
Description
Drainage Area
Description
DA A
(Pre-Dev.)
DA B
(Pre-Dev.)
DA A
(Post-Dev.)
DA B
(Post-Dev.)
DA C
(Post-Dev.)
Drainage Area (Am) in milesz =
0.0096
0.0034
0.0109
0.0021
0.0006
Runoff curve number CN=
58.6
56.7
76.4
77.3
81.7
Time of concentration (Tc)=
0.18
0.15
0.18
0.16
0.10
Rainfall distribution type=
II
II
II
II
II
Pond and swamp areas spread
throughout the watershed=
0
0
0
0
0
2. Frequency -years
1
2
10
1
2
10
1
2
10
1
2
10
1
2
10
3. Rainfall, P (24 hour)- inches
3.00
3.63
5.49
3.00
3.63
5.49
3.00
3.63
5.49
3.00
3.63
5.49
3.00
3.63
5.49
4. Initial Abstraction, la- inches
1.41
1.41
1.41
1.53
1.53
1.53
0.62
0.62
0.62
0.59
0.59
0.59
0.45
0.45
0.45
5. Compute la/P
0.47
0.39
0.26
0.51
0.42
0.28
0.21
0.17
0.11
0.20
0.16
0.11
0.15
0.12
0.08
6. Unit peak discharge, Qu- csm/in
500
625
775
425
625
825
775
800
825
825
850
875
975
1000
1000
7. Runoff, Qfrom Worksheet 2- inches
0.29
0.53
1.49
0.24
0.45
1.35
1.04
1.49
2.99
1.09
1.55
3.07
1.36
1.87
3.49
8. Pond and Swamp adjustment factor, Fp
1
1
1
1
1
1
1
1
1
1
1
1
1 1
1
1
9. Peak Discharge, Qp- cfs
where Qp=Qu Am Q Fp
1.39
3.16
11.06
0.34
0.96
3.77
Routed Through The
SWM Facility
Routed Through
The SWM Facility
1 0.83
1.17
2.18
WATERSHED SUMMARY
CN
Area, ac.
1-year Flow,
2-year Flow,
10-year Flow,
cfs
cfs
cfs
DA A (Pre-Dev.)
58.6
6.13
1.39
3.16
11.06
DA B (Pre-Dev.)
56.7
2.16
0.34
0.96
3.77
58.1
8.29
1.73
4.12
14.83
CN
Area, ac.
1-year Flow,
2-year Flow,
10-year Flow,
cfs
cfs
cfs
DAA (Post-Dev.)
76.4
6.97
DA B (Post-Dev.)
77.3
1.32
0.31
2.14
11.03
76.6
8.29
0.31
2.14
11.03
<- Wet Pond Routing Calcs (For Quantity Compliance)
Conservatively Assume a Clogged UGD for DA B where flows are
bypassed directly into the pond.
Brookhill Block 8B- Level II Wet Pond Routings
BasinFlow printout
INPUT:
Basin: Brookhill Block 8B- Level II Wet Pond Routings
9 Contour Areas
Elevation(ft)
Area(sf)
Computed Vol.(cy)
360.00
696.00
0.0
361.00
882.00
29.2
362.00
1301.00
69.3
364.00
2479.00
207.0
365.00
3508.00
317.3
366.00
5684.00
485.9
368.00
9145.00
1030.1
370.00
13133.00
1850.8
372.00
17744.00
2990.1
Start—Elevation(ft)
5 Outlet Structures
Outlet structure 0
Orifice
366.00 Vol.(cy) 485.94
name: Barrel
area (sf) 1.227
diameter or depth (in) 15.000
width for rect. (in) 0.000
coefficient 0.500
invert (ft) 364.720
multiple 1
discharge out of riser
Outlet structure 1
Orifice
name: Low -Flow Orifice
area (sf) 0.049
diameter or depth (in) 3.000
width for rect. (in) 0.000
coefficient 0.500
invert (ft) 366.000
multiple 1
discharge into riser
Page 1
Brookhill Block 8B- Level II Wet Pond Routings
Outlet structure 2
Orifice
name: Mid -Flow Orifices
area (sf) 0.196
diameter or depth (in) 6.000
width for rect. (in) 0.000
coefficient 0.500
invert (ft) 368.660
multiple 6
discharge into riser
Outlet structure 3
Weir
name: Riser
diameter (in) 36.000
side angle 0.000
coefficient 3.300
invert (ft) 369.500
multiple 1
discharge into riser
transition at (ft) 0.912
orifice coef. 0.500
orifice area (sf) 7.069
Outlet structure 4
Weir
name: Emergency Spillway
length (ft) 45.000
side angle 71.570
coefficient 3.300
invert (ft) 370.500
multiple 1
discharge through dam
4 Inflow Hydrographs
Hydrograph 0
SCS
name: 1-yr TR-55 SCS 24-hr Design Storm
Area (acres) 8.290
CN 76.600
Type 2
rainfall, P (in) 3.000
time of conc. (hrs) 0.1800
time increment (hrs) 0.0200
time limit (hrs) 30.000
fudge factor 1.00
routed true
peak flow (cfs) 9.696
peak time (hrs) 11.970
volume (cy) 1167.436
Page 2
Hydrograph 1
SCS
Brookhill Block 8B- Level II Wet Pond Routings
name: 2-yr TR-55 SCS 24-hr Design Storm
Area (acres)
8.290
CN
76.600
Type 2
rainfall, P (in)
3.630
time of conc. (hrs)
0.1800
time increment (hrs)
0.0200
time limit (hrs)
30.000
fudge factor
1.00
routed
true
peak flow (cfs)
13.878
peak time (hrs)
11.970
volume (cy)
1670.919
Hydrograph 2
SCS
name: 10-yr TR-55 SCS 24-hr Design Storm
Area (acres)
8.290
CN
76.600
Type 2
rainfall, P (in)
5.490
time of conc. (hrs)
0.1800
time increment (hrs)
0.0200
time limit (hrs)
30.000
fudge factor
1.00
routed
true
peak flow (cfs)
27.749
peak time (hrs)
11.970
volume (cy)
3340.952
Hydrograph 3
SCS
name: 100-yr TR-55 SCS 24-hr Design Storm
Area (acres)
8.290
CN
76.600
Type 2
rainfall, P (in)
8.990
time of conc. (hrs)
0.1800
time increment (hrs)
0.0200
time limit (hrs)
30.000
fudge factor
1.00
routed
true
peak flow (cfs)
56.788
peak time (hrs)
11.970
volume (cy)
6837.272
Page 3
Brookhill Block 8B- Level II Wet Pond Routings
OUTPUT:
Routing Method: storage -indication
Hydrograph 0
Routing Summary of
Peaks: 1-yr TR-55
SCS 24-hr Design Storm
inflow (cfs)
9.696
at
11.96
(hrs)
discharge (cfs)
0.306
at
13.52
(hrs)
water level (ft)
368.537
at
13.82
(hrs)
storage (cy)
1221.777
Hydrograph 1
Routing Summary of
Peaks: 2-yr TR-55
SCS 24-hr Design Storm
inflow (cfs)
13.878
at
11.96
(hrs)
discharge (cfs)
2.138
at
12.34
(hrs)
water level (ft)
369.041
at
12.34
(hrs)
storage (cy)
1420.208
Hydrograph 2
Routing Summary of
Peaks: 10-yr TR-55
SCS 24-hr Design Storm
inflow (cfs)
27.749
at
11.96
(hrs)
discharge (cfs)
11.029
at
12.14
(hrs)
water level (ft)
370.365
at
12.14
(hrs)
storage (cy)
2033.840
Hydrograph 3
Routing Summary of
Peaks: 100-yr
TR-55 SCS 24-hr Design Storm
inflow (cfs)
56.788
at
11.96
(hrs)
discharge (cfs)
54.141
at
12.00
(hrs)
water level (ft)
370.928
at
12.00
(hrs)
storage (cy)
2336.945
Mon Sep 09 07:52:29 EDT 2019
Page 4
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PIPE OUTLET CONDITIONS
• A
'IPE OUTLET TO FLAT
,REA WffH NO DEFINED
'HANNEL
I
3do (MIN.)
'IPE OUTLET TO WELL
)EFINED CHANNEL
-'r'�'�•
!:i%:ia:r• ::::::��� ;!�;i=lull
�.:..�:..•-
A —A
.!a:...:...:..,:•
mm CLOTH Ku IN W—sr: M=Mmmrn
FOR PR
APRONSECTION
NOTES: 1. •
BASKET,►
La IS THE LENGTH OF THE RIPRAP APRON AS CALCULATED
USING ►
PLATES2
��. :� ►I ►
INCHES.LESS THAN 6 �
Source: Va. DSWC
III - 157
Plate 3.18-1
9 VAC 25-870-66
(For Subareas A & B)
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.1.b.
"The peak discharge requirements for concentrated stormwater flow to natural stormwater
conveyance systems in subdivision 3 of this subsection shall be met."
Section B.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 B.3.a.
In accordance with the following methodology:
Allowed :S 1•F
Q Pre -Developed RV Pre -Developed) / RV Developed
Q Allowed
0.37 cfs Where: Qpre-Developed =
1.73 cfs
S Pre -Developed =
7.22
RV Pre -Developed =
0.28 in.
S Post -Developed =
3.06
RV post -Developed=
1.05 in.
I.F. =
0.80
Q Developed =
0.31 cfs
Section B.4 Limits of Analysis
The analysis terminates at the proposed SWM facility's outfall since subsection B.3.a is met.
9 VAC 25-870-66
(For Subareas A & B)
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 "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."
Section C.3 Limits of Analysis
The analysis terminates at the proposed SWM facility's outfall since subsection C.2.b is
met.
WATERSHED SUMMARY
10-year Flow,
CN
Area, ac.1-year Flow, cfs 2-year Flow, cfs
cfs
DA A (Pre-Dev.)
58.6
6.13 1.39 3.16
11.06
DA B (Pre-Dev.)
56.7
2.16 0.34 0.96
3.77
58.1
8.29 1.73 4.12
14.83
CN Area, ac,1-year Flow, cfs 2-year Flow, cfs 10-year Flow,cfs
DA A (Post-Dev.) 76.4 6.97 0.31 2.14 11.03
DA B (Post-Dev.) 77.3 1.32 0.00 0.00 0.00
76.6 8.29 0.31 2.14 11.03
Note:
The wet pond routing calcs (For Quantity Compliance) conservatively assume a clogged
UGD for DA B.
Virginia Runoff Reduction Method
Water Quality Calculations
(COMPLIANCE IS MET THROUGH THE BEST MANAGEMENT PRACTICE OF A
LEVEL II WET POND & THE PURCHASING OF NUTRIENT CREDITS.)
Please note, the standard VA DE4 VRRM spreadsheet is setup for most developments. However there are times when
this template does not completely conform with every development and the 'post -development project' area needs to
represent something other than the parcel's acreage or the limits of disturbance, which is the standard for Collins
Engineering.
In this case, Stella Lane is being reworked so the VRRM 'site' land cover consists of the proposed limits of disturbance
plus the small portion of Stella Lane being reconfigured. To ensure a conservative design, Stella Lane is assumed to have
zero impervious areas in the pre -development state for water quality and quantity, but its impervious areas are
accounted for the post -development water quality and quantity analyses. This is consistent with prior County
Engineering direction.
Additionally, the proposed development uses a downstream level II wet pond that receives runoff from upland areas
surrounding the proposed improvements, in addition to the actual onsite areas. Applying these offsite areas to 'DA A'
would yield inaccurate results since the pond's drainage area would exceed the site's land cover area. This would falsely
show a higher phosphorous removal rate credit. This is because it would incorrectly show the pond's treatment of a
larger drainage area (DA A). As a result, these offsite areas were omitted from the 'DA A' water quality analysis tab,
cementing further a conservative design. (FYI: These offsite areas were conservatively accounted for in the water
quantity analyses.)
This is an acceptable design concept since the development is required to treat the areas of proposed improvements.
Because this is a slight deviation from Collins Engineering's standard operating procedures though, the applicant wants to
point this out to the reviewer for his/her benefit.
DEQWrIl iaRungFieduction.MethodNewDem pmentCampliorrceSprerrdsheet - Verslon.3.0
02011 BMP Standards and SpedBations 02013 Draft SMP Standards and Specifkatlons
Project Name: Brookhill Development- Block 89 data Input ails
Date: 1/18/2019 anstant values
BMP Design Specifications List: 2013 Draft Stds & Specs calculation alb
Site Information
Post -Development Project (Treatment Volume and Loads)
"Land Cover faeresl
A Solis
I BSolls
CSulk
DSolls
Taal.
Fraert/OpenSpeRlavn)—undisturbed,
raected Caen or reforested land
Stllnurbed,
0.00
0.00
Managed Turf (saes) graded for
aids or other tort to be mowed/mara ed
4.02
4.02
Impervious cover (acres)
3.73
173
7.75'
Constants
Annual Ralnfall(Inches)
_43
-Tar et Rainfall Event (inches)
1.00
:Total Phosphorus (TP) EMC (mg/L)
0.26
:Total Nitrogen (TN) EMC (mg/L)
1.86
Target TP toad(lb/aae/yr)
D41
Pj(unitless correction factor)
0.90
A Soils
B Soils
C Soils
Forest/Open Space
0.02
0.03
0.04
Mareged Turf
0.15
0.20
0.22
V0.95
Impervious Cover
0.95
0.95
0.95
Forest/Open Space Cover (acres)
0.00
Treatment Volume 03623
(acre-ft)
Treatment Volume(cubic feet) 15,781
TP Load(lb/yr) 9.92
TN Load Ib r) —3
, ion
Weighted Rv(forest)
0.00
%Forest
0%
Managed Turf Cover (acreS)
.: 492
Weighted Rv(turf)
0.20
%Managed Turf
52%
Impervious Cover (acres)
3.73
Rv(impervious)
0.95
%Impervious
48%
Site Area (acres)
7.73
Site Rv
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