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.
Summary of volume reduction processes and BMPs associated with each process. Comments include qualifications and examples for the BMPs. Note that some BMPs occur in more than one process.
Link to this table
| 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] |