Tools to Improve Water Quality
Low Impact Development (LID) reduces environmental impact as compared with conventional development practices by filtering pollutants from stormwater runoff before it flows into creeks and rivers.Roads, parking areas, rooftops, and lawns turn rainfall into stormwater runoff, carrying polluted stormwater into creeks, sloughs and marshes, eventually flowing into Humboldt Bay and the Pacific Ocean. Motor oil, antifreeze, brake pad dust, fertilizers and pesticides, sediment, pet excrement, and heavy metals from roofing material can have significant impacts on water quality and aquatic life.Because of the increase in impervious surfaces associated with most development, much more—about 20-30 percent—becomes stormwater runoff. In a typical residential neighborhood, much less rainfall infiltrates the soil to be taken up by plants, and less evaporates into the atmosphere. The amount of runoff can also be a problem, causing erosion and flooding due to unnaturally-high volumes of water rushing across pavement and rooftops.
LID aims to control stormwater runoff close to the source, a new approach to conventional practices of collecting and disposing of stormwater off-site. This is achieved by reducing the amount of stormwater that needs to be treated by reducing the impervious footprint of a site, thereby reducing the amount of runoff. The end results are a reduction in runoff volume, reduced peak flow, and improved water quality.LID involves site-specific design features that generate less surface runoff, less pollution, less erosion, and less overall damage to lakes, streams, and coastal waters. It also reduces the need for expensive centralized conveyance systems.
Vegetated swales, or “bioswales,” are essentially shallow, sloped, grassy ditches that act as both stormwater conveyance and treatment systems. Pollutant removal in swales is accomplished via filtration through channel and side slope vegetation, infiltration into the channel bottom, and activity of soil microbes. Monitoring of swales has documented significant removals of metals and total suspended solids, though reductions in nutrients such as nitrates and phosphates have been variable.
LID works equally well in new development and redevelopment projects, and can also be used to retrofit existing development. In many jurisdictions, LID principles are mandated in new residential and commercial developments by local ordinance. More Info:
- Humboldt Low Impact Development Stormwater Manual
- Natural Resources Defense Council's Stormwater Strategies: LID
- Complete and Green Streets
- City of Portland’s Sustainable Storm Water Management Program – LID for streets
For Advocates:
