Volume reduction practices Volume reduction practices

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]