HomeMy WebLinkAboutSDP200900062 CalculationsShort Version BMP Computations For Worksheets 2 - 6
Albemarle County Water Protection Ordinance: Modified Simple Method
Plan: Free Bridge Office Water Resources Area:Development Area
Preparer:Dominion Engineering Date: 14- Sep -09
Project Drainage Area Designation Site and 14,013 S.F. of TM 78 -57B
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)
Pj 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 =1.17
C pollutant concentration, mg /I or ppm target phosphorus
f factor applied to RR
required treatment volume in cy, 0.5" over imperv. area = A(I)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
pre - development Area post - development Area
Roads Length Width subtotal Length Width subtotal
0 0 0 0
0 0 0 0
0 0
0 983 0
Driveways Length Width no.subtotal Length Width no.subtotal
and walks 0 0 0 0 0
0 0 0 0 0
0 0 0 1598
Parking Lots Area 1 Area 2 Area 3 Area 4 Area 1 Area 2 Area 3 Area 4
887 0 887 23527 0 23527
Gravel areas Area 1 Area 2 subtotal Area 1 Area 2 subtotal
0 0 0 x 0.70 =0 0 0 0 x 0.70 =0
Structures Area no.subtotal Area no.subtotal
0 0 0 6000 1 6000
0 0 0 0 0 0
0 0 0 0 0 6000
Actively - grazed pasture & Area Area
yards and cultivated turf x 0.08 =0 x 0.08 =0
Active crop land Area Area
0 x 0.25 =0 0 x 0.25 =0
Other Impervious Areas Area 1 Area 2 Area 3 Area 1 Area 2 Area 3
0 0 0 0 0
Impervious Cover 4%61%
I(pre)post)
Rv(post) V
0.60 48.0
New Development (For Development Areas, existing impervious cover <= 20 %)
C f I (pre) * Rv(pre) L(pre) L(post) RR RR Area Type
0.70 1.00 20% 0.23 1.65 4.31 2.65 62% Development Area
0.35 1.00 0% 0.08 0.30 2.15 1.86 86% Drinking Water Watersheds
0.40 1.00 1% 0.08 0.34 2.46 2.12 86% 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 1.65 4.31 2.82 65% Development Area
0.35 0.85 0% 0.08 0.30 2.15 1.90 88% Drinking Water Watersheds
0.40 0.85 1% 0.08 0.34 2.46 2.17 88% Other Rural Land
rev. 30 May 2002 JMK