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.