HomeMy WebLinkAboutSUB201300081 Calculations 2013-06-11 SHIM PROJECT MANAGEMENT
CIVIL ENGINEERING
LAND PLANNING
ENGINEERING :
Houndstooth
Preliminary Water Quality Map and Computations
June 7, 2013
Short Version BMP Computations
Albemarle County Water Protection Ordinance: Modified Simple Method
Plan: Houndstooth Water Resources Area: Drinking Water Watershed
Preparer: Lauren Gilroy Date: 06-Jun-13
Project Drainage Area Designation Site Area
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= i� 8.74 1
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)
I Item
Ipre-development Area ppost-development iArea
(Roads Length Width subtotal i ( Length Width subtotal j
01 o 01 Oi 01_. 211931
01 0 0( 1 01 Oj 0
1
I
01 0! 61 p1
,
1 0` 0 1 ' 01 211931
;Driveways Length Width no. subtotal (Length Width no. subtotal 1
and walks 01 01 of 0. 1601 10 5+ 80001
01 01 Oi 01 01 0; Oi o1
0' or _ i ) + 8000;
!Parking Lots 1 2 3 41 1 1 2 3 4J 1
1Gravelareas Area I 1 i Area i
I = 1 01 x0.70= 01
Structures Area no. subtotal I Area no. subtotal 1
I 0 0` O, 30001 31 90001
' 0 0 0 f 1 0. 0; 0'
� of of 0l 0; 1 _ ' of 9000!
!Actively-grazed pasture& Area i [ Area
•
yards and cultivated turf j Ix 0.08= 01 1 Ox 0.08= 1 01
IActive crop land Area ? Area
I ix 0.25= 01 1 ix 0.25= ! 0
OOther Impervious Areas i i
0
Impervious Cover g_a 0 1 10%f w %
l(pre) ((post_
Rv(post)i V
0.14 1 58.9 f
New Development(For Development Areas,existing impervious cover<=20%'
C 1 f I I(pre)* ! Rv(pre) ) L(pre) i L(post) 1 RR I %RR 1 Area Type
070 ' '1`00_ 20"-/0} 0.23 1 12.34 I 7.53 -4.81 i 64%1 Development Area
f ° �.;
00, 0% 0.05 1 1.34 1 3.76 ; 2.42 . 64% Drinking Water Watersheds
w'0 40 l'00" TY0 0.06 1 1.81 1 4.30 . 2.49 i 58%' Other Rural Land
*min.values
Redevelopment(For Development Areas,existing impervious cover>20%1
C , f I I(pre)* 1 Rv(pre) 1 L(pre) I L(post) 1 RR I %RR ° ;! Area Type
b » 0 70 p 90 20% 0.23 1 12.34 1 7.53 -3.58 I -48% Development Area
c "
F ; 0 35 0 85 O% 0.05 � 1.341 3.76 . 2.62 1 70%` Drinking Water Watersheds
, 0,40-i'" 0.85 1% 0.06 1.81 I 4.30 ; 2.76 64%1 Other Rural Land
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