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... absorb and transport large runoff events

What are Bioswales?

Bioswales are storm water runoff conveyance systems that provide an alternative to storm sewers. They can absorb low flows or carry runoff from heavy rains and snowmelt to storm sewer inlets or directly to surface waters. Bioswales improve water quality by enhancing infiltration of the first flush of storm water runoff and filtering the large storm flows they convey. About 30 to 40 percent of Montana’s annual precipitation comes from small rain events. Much of the value of bioswales comes from filtering nearly all of this water.

Photo of roadside bioswale planted with native sweetgrass.
This bioswale is planted with native sweetgrass (Hierochloe odorata.)

Photo of road ditch bioswale described in following sentence.
A road ditch can serve as a bioswale. The rock trench and wetland vegetation are notable features along with the natural drainageway in the background that serves as a bioswale for residential runoff.