Difference between revisions of "Summary of stormwater credits function"
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| − | + | <font size=3>'''Summary of stormwater credits function illustrating how to calculate water quality volume, channel protection and overbank storm volumes for different [[Better site design|Better Site Design]] credits.'''</font size><br> | |
| − | Link to this [[Summary of stormwater credits function|table]]. | + | Link to this [[Summary of stormwater credits function|table]]. |
<table class="sortable"> | <table class="sortable"> | ||
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<td>Surface impervious cover and disconnection</td> | <td>Surface impervious cover and disconnection</td> | ||
<td>Subtract DIA from site IC when computing V<sub>wq</sub></td> | <td>Subtract DIA from site IC when computing V<sub>wq</sub></td> | ||
| − | <td>Adjust CN for DIA to grass in good condition. | + | <td>Adjust CN for DIA to grass in good condition. Adjust T<sub>c</sub></td> |
</tr> | </tr> | ||
<tr> | <tr> | ||
<td>Rooftop disconnection</td> | <td>Rooftop disconnection</td> | ||
<td>Subtract DRA from site IC when computing V<sub>wq</sub></td> | <td>Subtract DRA from site IC when computing V<sub>wq</sub></td> | ||
| − | <td>Adjust CN for DIA to grass in good condition. | + | <td>Adjust CN for DIA to grass in good condition. Adjust T<sub>c</sub></td> |
</tr> | </tr> | ||
<tr> | <tr> | ||
Revision as of 18:24, 19 March 2013
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)