HomeMy WebLinkAboutSDP200800101 Calculations 1998-02-16Short Version BMP Computations For Worksheets 2 - 6
Albemarle County Water Protection Ordinance: Modified Simple Method
Plan: Example Water Resources Area
Preparer:Date:
Project Drainage Area Designation DA# 2
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 = 1.00
C pollutant concentration, mg /I 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)
ImFervious Cover Computation (values in feet & square feet)
Item
W ...
pre - development Area post
Roads Length Width subtotal j
0 0` 0'
0 _ 0 0
Q
0 0
Driveways Length Width no. subtotal Len
and walks 0 0 0 0'
0 0
Parking Lots 1 2 3 4
0 _..... 0
Gravel areas Area I Area
x 0.70 Q
Rv(post) V
L 0.05 0.0
I(pre)
Development Area
levelopment
T
Length Width subtotal
0`20 0'
0 0 0'
0 0 0
RR
0
no.subtotal
0 0 01
0 0 0;
0.31 711
2 3 4,'
I
New Development (For Development Areas existing impervious cover - 20 %)
C f I (pre) *Rv(pre)L(pre)L(post)RR
L(post)
RR
0.70 1.00 20%0.23 141 0.31 711
0.96 - 314%
360%
0.35 1.00 0%0.05 015 0.15 0.00
Drinking Water Watersheds
0%
0.40 1.00 1 %0.06 0.21 0.18 0.03 18%
min. values
x 0.70 =
I(post) t)
Area Type
Development Area
Drinking Water Watersheds
Other Rural Land
Redevelopment (For Development Areas, existing impervious cover > 20 %)
W .....
0 f I (pre) *Rv(pre)L(pre)L(post)RR % RR Area Type
0.70°0.90 20 %m 0.23 1.41 0.31 0.96 - 314%Development Area
0.35 0.85 0 %0.05 0.15 0.15 0.02 15%Drinking Water Watersheds
0.40 0.$5 1 %`0.06 0.21 0.18 0.00 0%Other Rural Land
Interim Manual, Page 70 rev. 16 Feb 1998 GEB