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:Tc – Time of Concentration (units: time)<br>V<sub>wq</sub> – Water quality volume, as defined by relevant MPCA sizing rule<br>
 
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:IC - Impervious area of site (acres)</font size>
 
:IC - Impervious area of site (acres)</font size>
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Latest revision as of 20:38, 4 August 2022

Summary of stormwater credits function illustrating how to calculate water quality volume, channel protection and overbank storm volumes for different Better Site Design credits.
Link to this table.

Stormwater credit Adjusted water quality volume Channel protection and overbank storms
Natural area conservation Subtract CA from site IC when computing Vwq Adjust CN for CA to woods in good condition
Site reforestation/prairie restoration Subtract 1/2 RA from site IC when computing Vwq Adjust CN for RA to woods or prairie in fair condition
Streams and shoreline buffers Subtract ADB from site IC when computing Vwq Adjust CN for ADB to woods in good condition
Surface impervious cover and disconnection Subtract DIA from site IC when computing Vwq Adjust CN for DIA to grass in good condition. Adjust Tc
Rooftop disconnection Subtract DRA from site IC when computing Vwq Adjust CN for DIA to grass in good condition. Adjust Tc
Grass channels Subtract GA from site IC when computing Vwq Adjust Tc

Note: Unless otherwise noted, all units below are measured in acres

CA = combined area of all natural areas conserved at site
RA – Total area of site reforestation or prairie restoration
ADB – Total area draining to buffer with appropriate flow path distance
DIA – Total area of surface impervious cover that can be effectively disconnected
DRA – Aggregate rooftop area that can be effectively disconnected
GA - total non-roadway area draining to swale (rooftop, yard and driveway)
CN – Runoff curve number for area (units: dimensionless) (see Ch.8 and App. B)
Tc – Time of Concentration (units: time)
Vwq – Water quality volume, as defined by relevant MPCA sizing rule
IC - Impervious area of site (acres)

This page was last edited on 4 August 2022, at 20:38.