HomeMy WebLinkAboutSDP200800012 Calculations 2008-01-18Short Version BMP Computations For Worksheets 2 - 6
Albemarle County Water Protection Ordinance: Modified Simple Method
Plan: South Pantops Condos Water Resources Area
Preparer: ABB Date: 18- Jan -08
Project Drainage Area Designation BF -1
L storm pollutant export in pounds, L = [P(Pj)Rv /12 ] [ C(A)2.72 ]
Rv mean runoff coefficient, Rv = 0.05 + 0.009(1)
Pi small storm correction factor, 0.9
1 percent imperviousness
P annual precipitation, 43" in Albemarle
A project area in acres in subject drainage area, A = 3.33
C pollutant concentration, mg /1 or ppm target phosphorus
f factor applied to RR
V required treatment volume in cy, 0.5' over imperv. area = A(1)43560(0.5/12)/27
RR required removal , L(post) - f x L(pre)
RR removal efficiency, RR100 /L(post)
Impervious Cover Computation (values in feet & square feet)
Item
New Development: Development
Area
pre - development Area post - development
Roads Length Width subtotal Length Width
230
0
0
0 0
Length Width no.
1148 20
1175 5
0 18 12
1 2
0 6560
Area
0 x 0.70 =
C
Actively - grazed pasture & Area
yards and cultivated turf 0 x 0.08 = 0
Active crop land Area
x 0.25 = 0
Other Impervious Areas
0
Impervious Cover 0%
I(pre)
subtotal
20 4600
0 0
0 0
0 0
subtotal
1 22960
1 5875
4 864
3 4
0
Area no. subtotal
8400 7 58800
0 0 0
0 0 0
Area
15000 x 0.08 =
Area
x 0.25 =
Rv(post)V
0 0 0
RR RR
0 0 0
0.23 4.70
0 0 0
Development Area
New Development (For Development Areas, existing
0 0 0
Driveways Length Width no.subtotal
L(post)
and walks 0 0 0 0
0.23
0 0 0 0
0.35
0 0 0 0
Parking Lots 1 2 3 4
1%
0
0.69 7.89 7.21 91%
Gravel areas Area
x 0.70
Structures Area no.subtotal
0 0 0
0 0 0
0 0 0
230
0
0
0 0
Length Width no.
1148 20
1175 5
0 18 12
1 2
0 6560
Area
0 x 0.70 =
C
Actively - grazed pasture & Area
yards and cultivated turf 0 x 0.08 = 0
Active crop land Area
x 0.25 = 0
Other Impervious Areas
0
Impervious Cover 0%
I(pre)
subtotal
20 4600
0 0
0 0
0 0
subtotal
1 22960
1 5875
4 864
3 4
0
Area no. subtotal
8400 7 58800
0 0 0
0 0 0
Area
15000 x 0.08 =
Area
x 0.25 =
Rv(post)V
Rv(pre)L(pre)L(post)RR RR Area Type
0.68 155.6
0.23 4.70 13.81 9.58 69%Development Area
New Development (For Development Areas, existing impervious cover <= 20 %)
0.05
C f I (pre) *Rv(pre)L(pre)L(post)RR % RR Area Type
0.70 1.00 20%0.23 4.70 13.81 9.11 66%Development Area
0.35 1.00 0%0.05 0.51 6.91 6.40 93%Drinking Water Watersheds
0.40 1100 1%0.06 0.69 7.89 7.21 91%Other Rural Land
min. values
Redevelopment (For Development Areas, existing impervious cover > 20 %)
C f I (pre) *Rv(pre)L(pre)L(post)RR RR Area Type
0.70 0.90 20%0.23 4.70 13.81 9.58 69%Development Area
0.35 0.85 0%0.05 0.51 6.91 6.47 94%Drinking Water Watersheds
0A0 0,85 1%0.06 0.69 7.89 7.31 93%Other Rural Land
Area
VIII',
29699
6560
0
58800
iilelf,
0
0
70%
I(post)
Interim Manual, Page 70 rev. 16 Feb 1998 GEB