When stormwater gathers on nonabsorbent surfaces like roofs, streets and sidewalks, it provides a vehicle for transporting pollutants such as metals, chemicals, debris and bacteria. While most residential and urban areas use sewer systems and storm drains to prevent pooling water, stormwater runoff is then channeled into nearby bodies of water such as lakes, rivers and oceans with these pollutants in tow.
Alpha Environmental provides environmentally-friendly methods to manage stormwater runoff. We offer bioswales and bioretention basins that filter and slow the drainage of stormwater, allowing it to be properly treated before making its way into sensitive habitats. We also provide regular maintenance and annual check-up services to keep these systems working as designed.
Bioretention Basins
Bioretention areas are landscaped depressions or shallow basins that slow and treat stormwater on site. Common along roadways or in parking lot islands, bioretention basins mimic the ways in which pollutants are removed from forested areas by passing stormwater through layers of soil, mulch and plants that act as filters. The treated water is then directed to drains and/or surrounding bodies of water.
Bioretention areas are extremely useful in heavy rain conditions, as they often allow water to pool up to several feet before passing it through to an overflow outlet. This helps to prevent flooding.
Bioretention basins are typically composed of seven elements:
- A grass buffer strip that reduces the speed of runoff stormwater and removes debris.
- Vegetation that helps remove water through evaporation. Plants also remove excess nutrients through nutrient cycling.
- A shallow ponding area that provides storage for excess stormwater and its subsequent evaporation. This area also aids in the settlement of solid and liquid debris.
- Mulch, which provides an organic layer that encourages the biological degradation of petroleum-based pollutants. Mulch also aids in filtering out pollutants and reduces soil erosion.
- Engineered soils to support plant growth, increase nutrient uptake and provide water storage. These soils should include some clay to absorb pollutants such as hydrocarbons, heavy metals and nutrients.
- A sand bed, which provides drainage, allows air into the planting soil and aids in flushing pollutants.
- An underdrain system to channel excess treated stormwater to a storm drain system or nearby bodies of water.
Bioretention basins are perfect for small areas like residential neighborhoods or shopping centers, as they contribute to urban aesthetics while restoring natural water cycles.
Bioswales and Rain Gardens
Bioswales and rain gardens are vegetated, shallow, landscaped areas designed to capture, treat and infiltrate stormwater runoff as it moves downstream. While the two systems are similar, bioswales are designed to filter and carry stormwater to storm inlets or nearby waterways. In contrast, rain gardens are specifically designed to filter and absorb stormwater in place of redirecting it.
Bioswales and rain gardens should be composed of diverse, deep-rooted, native vegetation to increase the amount of time water spends in the area. The sides of these shallow areas should be slightly sloped to allow for the collection of stormwater.
These systems are often used in urban areas near cities or busy streets, where stormwater is more likely to collect on nonabsorbent surfaces, such as:
- Parking lots
- Rooftops
- Sidewalks
- Driveways
Both bioswales and rain gardens are excellent for filtering water on a smaller scale. The majority of precipitation comes from small rain events, during which these systems can capture and filter nearly all of the resulting water.
Bioretention Systems in Portland, OR
Once installed, bioswales and bioretention areas require regular maintenance and annual checkups, just like regular storm drains and inlets. Contact us today to learn more about our environmentally friendly stormwater management systems!
