A bioswale is a linear, shallow, planted depression that guides water away from its entry point on the property (downspouts, uphill properties, etc.) and towards a rain garden. Bioswales are also useful for directing water from a rain garden (in the event the rain garden overflows) and towards its exit point on the property or simply to guide water as it moves through the property. These swales are planted or seeded with moisture-loving plant species that are also tolerant of seasonal fluctuations in moisture levels. The plants’ structure aids in reducing the flow rate of stormwater runoff and enhances the soil’s absorption of water even before it enters the rain garden retention area or exit point.
Bioswales can be constructed independent of a rain garden if circumstances don’t allow for the installation of a rain garden (such as limited space or steep, narrow sites). In this case, they guide water to existing storm-water systems such as storm drains in roadways, etc.
Where volume and velocity of water is high, a constructed dry creek bed made of gravel may substitute for a vegetated bioswale. Vegetated swales are preferred, however, as Meramec River gravel is typically the source of gravel in the Greater St. Louis Region, and gravel mining is known to be a major contributor to water quality degradation in the Meramec River watershed.