Warning: Note the following table provides general information about volume reduction. It is not intended for determining Construction Stormwater permit compliance, although the table includes a column discussing the applicability of the practice to permit compliance.
| Process | BMP | Comments | Used for CSW permit compliance? |
|---|---|---|---|
| Infiltration | Low impact development/better site design/sustainable development | Includes such things as reduced street and sidewalk width, less curb and gutter drainage, scattered bioretention, shared pavement. | Yes if water is retained on site, typically through infiltration |
| Trench or basin | Must be properly engineered in adequate soils; proper maintenance essential | Yes [1] | |
| Perforated sub-surface pipes, tanks and storage systems | Expensive but effective and space-saving. | If part of an infiltration stormwater practice | |
| Disconnected imperviousness | Includes primarily rooftop drains and roadway/parking surfaces | By itself, disconnection does not meet CSW permit requirements. Runoff must be diverted to an infiltration stormwater practice | |
| Pervious (porous pavement) | Includes a number of paving and block methods, or simple parking on reinforced grassed surfaces. | Yes [2] | |
| Bioretention (if contains infiltration element) | Some bioretention facilities are designed to infiltrate. | Yes if bioinfiltration. Biofiltration practices may achieve some volume reduction that can be credited toward permit compliance. [3] | |
| Evapotranspiration | Bioretention (rain gardens) | Exposes runoff water to plant roots for uptake; can be under-drained and still effective. | |
| Vegetated swales | Provides water a chance to soak into the ground and be filtered as it flows. | Yes, though swales typically achieve limited volume reduction unless designed with check dams and/or occurring on permeable soils [4] | |
| Wetland/pond storage | Combination of standing water surface and vegetative root exposure yields volume reductions. | No | |
| Vegetated drainage corridor | Connecting numerous features increases opportunities. | No | |
| Recessed road/parking drainage | Routing paved surface runoff to vegetated sump areas keeps it out of receiving waters. | No, unless part of an infiltration practice | |
| Storage | Rain barrel/cistern | Small-scale runoff collectors keep water around for later re-use or slow release. | Yes if captured water is infiltrated or otherwise used on site |
| Rooftop (green roof) | Storage on a roof prevents water from leaving the site; combining with vegetation (engineered green roof) makes it even better. | Yes if captured water is retained on site (typically through evapotranspiration) | |
| Conveyance | Vegetated swale | Provides water a chance to soak into the ground and be filtered as it flows. | Yes, though swales typically achieve limited volume reduction unless designed with check dams and/or occurring on permeable soils [5] |
| Filter strips/buffers | Variation of vegetated swale with side slope protection. | No | |
| Landscaping | Low Impact Development/Better Site Design | Includes such things as scattered bioretention, shared pavement, native or prairie plantings. | Yes if water is retained on site, typically through infiltration |
| Bioretention (rain gardens) | Exposes runoff water to plant roots for uptake, can be under-drained and still effective. | Yes if bioinfiltration. Biofiltration practices may achieve some volume reduction that can be credited toward permit compliance. [6] |