[Stand in for swale crediting page]
NOTE: The methods described on this page can also be used to calculated credits for high-gradient stormwater step-pool.
| TSS | TP | PP | DP | TN | Metals | Bacteria | Hydrocarbons |
|---|---|---|---|---|---|---|---|
| 68 | link to table | link to table | link to table | 35 | 80 | 0 | 80 |
| NOTE: removal efficiencies are 100 percent for water that is infiltrated. | |||||||
| TSS=total suspended solids; TP=total phosphorus; PP=particulate phosphorus; DP=dissolved phosphorus; TN=total nitrogen | |||||||
Warning: Models are often selected to calculate credits. The model selected depends on your objectives. For compliance with the Construction Stormwater permit, the model must be based on the assumption that an instantaneous volume is captured by the BMP.
Credit refers to the quantity of stormwater or pollutant reduction achieved either by an individual best management practice (BMP) or cumulatively with multiple BMPs. Stormwater credits are a tool for local stormwater authorities who are interested in
- providing incentives to site developers to encourage the preservation of natural areas and the reduction of the volume of stormwater runoff being conveyed to a best management practice (BMP);
- complying with permit requirements, including antidegradation (see Construction permit; Municipal (MS4) permit);
- meeting the MIDS performance goal; or
- meeting or complying with water quality objectives, including total maximum daily load (TMDL) wasteload allocations (WLAs).
This page provides a discussion of how dry swales can achieve stormwater credits. Swales with and without underdrains are both discussed, with separate sections for each type of system as appropriate.