Water Quality Improvements
For purposes of the LA River Project, it is important to understand that significant water quality improvement efforts will be undertaken by municipalities draining into the river, and that implementation of Best Management Practices (BMPs)1 will provide significant benefit to water quality. As part of the Project, there will be a complimentary emphasis on regional BMPs that can provide meaningful reductions of pollutant loads, while also providing environmental and social benefits to surrounding communities. It is recognized that facilities treating significant drainage areas can provide significant value in terms of water volume treated, but are often limited by size and don’t address upstream water quality needs. Facilities treating smaller areas may have greater capture efficiencies and can often be located upstream of river confluences. It is anticipated that the combined assessment of benefits – water quality performance, with water resources, and other environmental benefits – will be considered in Project-related proposed strategies.
Rendering of a typical biofiltration unit cross-section, located within a parking lot median (Geosyntec Consultants, Inc.). Runoff from the parking lot enters the median through a curb cut and then drains through the engineered media, where it undergoes physical and biological treatment. Treated runoff that is not absorbed or evapotranspirated then re-enters the storm drain system through an underdrain.
Water quality improvement strategies, regionally referred to as BMPs encompass both structural measures (measures that physically clean the water, removing pollutants) and institutional measures (that focus on policy, incentives, education, and enforcement). These BMPs need to address both wet-weather stormwater and dry-weather urban runoff conditions. The EWMPs developed by the municipalities that own stormwater systems embraced a combination of approaches. The first priority being the institutional measures that are more easily implementable and require less public capital. The second priority would be distributed, smaller-footprint projects, consistent with concepts of green infrastructure and low impact development. These distributed BMPs include the development of green streets, and multi-use stormwater pocket parks.
Biofiltration units installed along sidewalks are one example of green infrastructure and are used to treat sidewalk runoff and rooftop runoff from adjacent buildings, as well as beautify the landscape of urban environments and relieve the Heat Island Effect (Geosyntec Consultants, Inc.).
The most complex BMPs are regional in nature, often requiring participation from multiple jurisdictions, but also providing multiple benefits. In addition to stormwater quality, if strategically located these projects have the potential to provide ground water recharge benefits, offsetting demands of imported water. These larger centralized BMPs also offer opportunities for public park development, providing passive and sometimes active recreational opportunities which are particularly valuable in park-deficient communities; they also offer potential habitat development, which has educational and social value. Examples of centralized BMPs include regional treatment wetlands, regional infiltration/recharge facilities, and multi-use detention facilities with treatment to offer direct use.
Example Southern California regional stormwater wetlands (Ballona Freshwater Marsh)
Example Southern California regional stormwater wetlands (Mill Creek Wetlands)
Example Regional infiltration and recharge facility (Tujunga Spreading Grounds and Sun Valley Park)
Example multi-use detention and treatment facility (Malibu Legacy Park)
1Structural and non-structural systems used to mitigate antropogenic impacts on storm water quantity and quality.
Ballona Freshwater Marsh, Geosyntec Consultants, Inc.
Mill Creek Wetlands, New Model Colonies, Ontario, CA
Tujunga Spreading Grounds (LADWP) and Sun Valley Park (LACFCD)
Malibu Legacy Park, Geosyntec Consultants, Inc.