HomeMy WebLinkAboutSDP200700148 CalculationsGLc 77 4'L r31,.)3
Modified Simple Method Worksheets
Divide the Site into Drainage Areas — Worksheet 1
Calculate the area in acres for each drainage area, and label each drainage area on the plan. It
will be necessary to fill out the following series of worksheets for each drainage area.
Drainage Area 1: 6.6 acres (on- site);acres (off- site); G- S total acres
Drainage Area 2:acres (on- site);acres (off - site);total acres
Drainage Area 3:acres (on- site);acres (off - site);total acres
Drainage Area 4:acres (on- site);acres (off - site);total acres
Drainage Area 5:acres (on- site);acres (off - site);total acres
Drainage Area 6:acres (on- site);acres (off - site);total acres
Drainage Area 7:acres (on- site);acres (off - site);total acres
Total (On -site) Area = 6 acres
05 February
WR -8
Calculate Pre - Development Impervious Cover (I pre) - Worksheet 2
Calculate I(pre) using actual site information for each drainage area (on -site acres only) as
identified in Worksheet 1. If the project is phased, include only the active phase(s).
0
DRAINAGE AREA # 1
ON -SITE AREA C.- S ACRES (on -site drainage area size)
Roads: length (ft) x width (ft) for all roads square feet
I Driveways: average length (ft) x average width (ft) x number of driveways =square feet
Parking Lots: square footage square feet
Gravel Areas: square footage x 0.70 square feet
Structures (including houses):
sum of actual square footage for all structures, OR
average house square footage x number of houses square feet
Actively - grazed pasture (livestock present), Yards & areas of cultivated turf:
actual square footage of areas x 0.08, OR
average yard area x number of yards x 0.08 .square feet
Active crop land: square footage x 0.25 square feet
Other Impervious Areas square feet
Total Equivalent Impervious Area =square feet sum of all the above values)
3(pre) Total Equivalent Impervious Cover (sq 41) x 100 b
43560 sq ft per acre /on -site drainage area (acs.)
DRAINAGE AREA #
ON -SITE AREA ACRES (on -site drainage area size)
Roads: length (ft) x width (ft) for all roads square feet
Driveways: average length (ft) x average width (ft) x number of driveways =square feet
Parking Lots: square footage square feet
Gravel Areas: square footage x 0.70 square feet
Structures (including houses):
sum of actual square footage for all structures, OR
average house square footage x number of houses square feet
Actively - grazed pasture (livestock present), Yards & areas of cultivated turf:
actual square footage of areas x 0.08, OR
average yard area x number of yards x 0.08 .square feet
Active crop land: square footage x 0.25 square feet
Other Impervious Areas square feet
Total Equivalent Impervious Area =square feet sum of all the above values)
I(pre) Total Equivalent Impervious Cover (sq ft) x 100
43560 sq ft per acre /on -site drainage area (acs.)
05 February 2003
WR -8
Calculate Pre- Development Phosphorus Load (Lpre) — Worksheet 3
Use the following table to calculate L(pre) based on the water resources area in which the project
is located.
Water Resources Area L(pre) =
Development Area, where I(pre) is less than 1.41 x A
or equal to 20%
Development Area, where I(pre) is greater 6.14 x [0.05 + (0.009)(Ipre)] x A
than 20%
Water Supply Protection Area, no existing 0.15 x A
impervious cover (do not count existing
equivalent impervious cover from pasture or
crop land)
Water Supply Protection Area, site with 3.07 x [0.05 + (0.009)(Ipre)] x A
existing impervious cover
Other Rural Land, no existing impervious 0.21 x A
cover (do not count existing equivalent
impervious cover from pasture or crop land)
Other Rural Land, site with existing 3.51 x [0.05 + (0.009)(Ipre)] x A
impervious cover
L(pre) = Pre - Development Phosphorus Load (pounds/year)
I (pre) = Pre - Development Equivalent Impervious Cover
expressed in whole numbers from Worksheet 2)
A On -Site Drainage Area (acres)
DRAINAGE AREA #
ON -SITE AREA 0 ACRES (on -site drainage area size)
L (pre) = 6 pounds per year (annual loading)P Po P Y g)
1
05 February 2003
WR -8
NNW
Worksheet 3 — Continued)
DRAINAGE AREA #
ON -SITE AREA ACRES (on -site drainage area size)
L (pre) =pounds per year (annual loading)
DRAINAGE AREA #
ON -SITE AREA ACRES (on -site drainage area size)
L (pre) =pounds per year (annual loading)
DRAINAGE AREA #
ON -SITE AREA ACRES (on -site drainage area size)
L (pre) =pounds per year (annual loading)
DRAINAGE AREA #
ON -SITE AREA ACRES (on -site drainage area size)
L (pre) =pounds per year (annual loading)
DRAINAGE AREA #
ON -SITE AREA ACRES (on -site drainage area size)
L (pre) =pounds per year (annual loading)
1
DRAINAGE AREA #
ON -SITE AREA ACRES (on -site drainage area size)
L (pre) =pounds per year (annual loading)
05 February 2003
WR -8
Calculate Post - Development Ultimate Impervious Cover (I post) - Worksheet 4
Use the following worksheet to calculate I(post) using assumed figures for build -out of the
project, including roads, houses, driveways, yards, etc.
DRAINAGE AREA # g, 0
ON -SITE AREA ACRES (on -site drainage area size)
Roads: length (ft) x width (ft) for all roads square feet
Driveways: average length (ft) x average width (ft) x number of driveways =square feet
Parking Lots: square footage square feet
Gravel Areas: square footage x 0.70 square feet
Structures (including houses):
sum of actual square footage for all structures, OR
average house square footage x number of houses square feet
Actively - grazed pasture (livestock present), Yards & areas of cultivated turf:
actual square footage of areas x 0.08, OR
average yard area x number of yards x 0.08 .square feet
Active crop land: square footage x 0.25 square feet
Other Impervious Areas square feet
Total Equivalent Impervious Area = 2L'2, 5 t3C7 square feet sum of all the above values)
I(post) Total Equivalent Impervious Cover (sq ft) x 100 6 %
43560 sq ft per acre /on -site drainage area (acs.)_ _
DRAINAGE AREA #
ON- SI'Z'E AREA ACRES (on -site drainage area size)
Roads: length (ft) x width (ft) for all roads square feet
Driveways: average length (ft) x average width (ft) x number of driveways =square feet
Parking Lots: square footage square feet
Gravel Areas: square footage x 0.70 square feet
Structures (including houses):
sum of actual square footage for all structures, OR
average house square footage x number of houses square feet
Actively - grazed pasture (livestock present), Yards & areas of cultivated turf:
actual square footage of areas x 0.08, OR
average yard area x number of yards x 0.08 .square feet
Active crop land: square footage x 0.25 square feet
Other Impervious Areas square feet
TotaFrjuivalent Impervious Area =square fee sum of all the above values)
I(post) Total Equivalent Impervious Cover (sq ft) x 100
43560 sq ft per acre /on -site drainage area (acs.)
05 February 2003
WR -8
Noe
Calculate Post - Development Phosphorus Load (L post) — Worksheet 5
Use the following table to calculate L(post) based on the water resources area in which the
project is located.
Water Resources Area L(post) =
Development Area 6.14 x [0.05 + (0.009)(Ipost)] x A
Water Supply Protection Area 3.07 x [0.05 + (0.009)(Ipost)] x A
Other Rural Land 3.51 x [0.05 + (0.009)(Ipost)] x A
L(post) = Post-Development Phosphorus Load (pounds/year)P P P P
I (post) = Post - Development Equivalent Impervious Cover
expressed in whole numbers from Worksheet 4)
A On -Site Drainage Area (acres)
DRAINAGE AREA # I
ON- SI "I'E AREA ACRES (on -site drainage area size)
L (post) = 2 7. pounds per year (annual loading)
DRAINAGE AREA #
ON -SITE AREA ACRES (on -site drainage area size)
L (post) =pounds per year (annual loading)
DRAINAGE AREA #
ON -SITE AREA ACRES (on -site drainage area size)
L (post) =pounds per year (annual loading)
05 February 2003
WR -8
Calculate Pollutant Removal Requirement — Worksheet 6
RR Pollutant) Removal Requirement = L post — ( L pre x f)pounds per year)
Where "f" is a factor applied to the Removal Requirement based upon the Conditions
described below.
RR = Overall BMP Pollutant Removal Efficiency = ( RR x 100 ) / L post percent)
Condition 1 — "No Existing Impervious Cover" ; f = 1.0
This condition does not include equivalent impervious cover from pasture/crop land. It
includes "new development" in all water resources areas and "adding impervious cover to
existing sites" when existing impervious cover is within:
Development Area and is Less than or equal to 20%
Water Supply Protection Area and is 0%
Other Rural Land and is less than or equal to 1%
Condition 2 — "Adding Impervious Cover To Sites With Existing Impervious Cover" in the
Development Areas ; f= 0.90
This condition includes "adding impervious cover to existing sites" when existing
impervious cover is greater than 20% or is designated as "infill and redevelopment ".
Condition 3 — "Adding Impervious Cover To Sites With Existing Impervious Cover" in the
Water Supply Protection Area or Other Rural Land ; f= 0.85
This condition includes "adding impervious cover to existing sites" when existing
impervious cover is within:
Water Supply Protection Area and is greater than 0%
Other Rural Land and is greater than 1%
Designated as " infill and redevelopment"
1 .
DRAINAGE AREA # Condition:2 3
L post = 276 Lpre= 9.6 RR= f8_o RR= 6s
05 February 2003
WR -8
Noe
Worksheet 6 — Continued)
DRAINAGE AREA #Condition: 1 2 3
L post =Lpre=RR=RR=
DRAINAGE AREA #Condition: 0 1 0 2 0 3
L post =Lpre=RR=RR=
DRAINAGE AREA #Condition: 1 0 2 0 3
L post =L pre =RR =RR =
DRAINAGE AREA #Condition: 1 2 3
L post =L pre =RR =RR
DRAINAGE AREA #Condition: 0 1 0 2 0 3
L post =L pre =RR =RR =
DRAINAGE AREA #Condition: 0 1 0 2 0 3
L post =L pre =RR =RR =
DRAINAGE AREA #Condition: 0 1 0 2 3
T post =Lpre=RR=RL.
05 February 2003
WR -8