Current stormwater management professionals recognize that stormwater quality and quantity are integrated. The historic management method has been to construct connected impervious area and conveyance infrastructure to get rid of surface runoff. This management method conveys all storm events, both large and small, to drainage ways, and the resulting flows contribute to channel scouring, widening, down-cutting and general modifications to the natural receiving waterways. This has degraded the natural environment along receiving waterways and increases the need for expensive restorative maintenance and repairs by local jurisdictions.
We encourage management practices and land development technologies that promote the absorption of smaller, more frequent precipitation events (i.e., source controls) to minimize impacts on receiving waters. The Urban Drainage and Flood Control District provides planning and design guidance through their Urban Storm Drainage Criteria Manual Volume 3. Much of it is based on the fact that the Denver Metropolitan area and much of the eastern high plains of Colorado along the foothills have a mean storm depth of 0.4 inches and that 80% of runoff events can be treated by capturing the Water Quality Capture Volume (WQCV). The WQCV is based on approximately 0.6 inches of precipitation during a storm event.
LID techniques and runoff volume reduction principles provide many benefits:
- Keeps more pollutants out of waterways
- Reduces the size and cost of stormwater collection and conveyance infrastructure when compared to typical street drainage, concrete swale, ditch, and pipe designs
- Reduces the volume required for detention and WQCV facilities
- Significantly reduces scour, degradation and habitat modification in receiving waterways
The Stormwater Quality Committee seeks to promote stormwater management techniques for the built environment to improve surface runoff water quality, protect receiving water quality, and protect aquatic and riparian habitat by facilitating discussion, information exchange, and education regarding:
- Stormwater runoff reduction (LID) BMPs
- The Four-Step Process, outlined in Urban Drainage and Flood Control District’s Criteria Manual, Volume 3
- Other techniques that minimize the impacts of land-use changes and human activities on receiving waters
These techniques will be promoted through field trips, photo database, identified training opportunities, and the annual CASFM conference.