Bioswales are linear, shallow, vegetated channels that convey stormwater from one point to another. Oftentimes, they are used to guide runoff from its entry point on the property (downspouts, uphill properties, etc.) towards a nearby rain garden, dry well or other structure. Bioswales are not just ditches under another name, however, they must be carefully designed and maintained to function properly. The vegetation in swales helps to trap pollutants (suspended solids and trace metals), reduce the velocity of stormwater runoff, and encourage infiltration. In some cases, street-side bioswales can replace curb and gutter systems, as well as storm sewers.
SEMCOG’s Low Impact Development Manual for Michigan: A Design Guide for Implementers and Reviewers
p. 315 – 326