HomeMy WebLinkAboutSDP201400038 Calculations 2013-06-17 Short Version BMP Computations`4119 ''isof
Albemarle County Water Protection Ordinance: Modified Simple Method
Plan: Faith Christian Center International Water Resources Area: Other rural areas
Preparer: Brian P.Smith, PE Date: 17-Jun-13
Project Drainage Area Designation The entire lot
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
I percent imperviousness
P annual precipitation,43"in Albemarle
A project area in acres in subject drainage area, A= 9.48
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 16487 Septic access 0 0 3404
0 0 0 Well access 0 0 1864
0 0 0 0
O 16487 0 5268
Sidewalks Length Width no. subtotal Length Width no. subtotal
0 0 0 0 0 0 0 8669
0 0 0 0 0 0 0 0
O 0 0 8669
Parking Lots 1 2 3 4 1 2 3 4
0 0 0 62875 62875
Gravel areas Area 3947 Area
2914 x 0.70= 4802.7 x 0.70= 0
Structures Area no. subtotal Area no. subtotal
2561 1 2561 18875 1 18875
653 19 12407 0 0 0
1947 1 1947 16915 0 18875
Actively-grazed pasture& Area Area
yards and cultivated turf 0 x 0.08= 0 0 x 0.08= 0
Active crop land Area Area
x0.25= 0 x0.25= 0
Other Impervious Areas
concrete pads 78 Retaining walls 1150
Impervious Cover 9% 23%
l(pre) l(post)
Rv(post) V
0.26 149.4
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 13.39 15.19 1.80 12% Development Area
0.35 1.00 0% 0.13 3.88 7.60 3.71 49% Drinking Water Watersheds
0.40 1.00 1% 0.13 4.44 8.68 4.24 49% 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 13.39 15.19 3.14 21% Development Area
0.35 0.85 0% 0.13 3.88 7.60 4.30 57% Drinking Water Watersheds
0.40 0.85 1% 0.13 4.44 8.68 4.91 57% Other Rural Land