Dominguez Gap Wetlands Kerjon Lee, Public Affairs Manager, and Mark Pestrella, Assistant Deputy Director, Watershed Management Division, Los Angeles County Department of Public Works, Alhambra, California
he Dominguez Gap Wetlands is located adjacent to the Los Angeles River—a 51-mile waterway that is almost entirely lined with concrete. This main artery of the flood control system in Los Angeles County provides drainage for an 834-square-mile (2,160 km2) watershed inhabited by approximately nine million people. As a result of dense urbanization within the watershed, the Los Angeles River is subject to heavily polluted flows laden with trash, debris, metals, bacteria and other pollutants. Faced with competing geographic and environmental constraints, the Los Angeles County Flood Control District identified an innovative solution to address water quality concerns while providing other benefits. In 1996, the Flood Control District and local stakeholders adopted the Los Angeles River Master Plan. This master plan led the way to river revitalization efforts in numerous watersheds throughout the county. The plan also identified key areas where large-scale projects could provide flood risk management, water quality improvement, groundwater recharge, and open space opportunities. As a result of this plan, the Flood Control District set out to design a multi-benefit facility that would recharge the West Coast Groundwater Basin, restore native habitat, and improve the quality of dry-weather flows through a natural treatment process while continuing to provide flood protection to the surrounding community. That concept became one of five demonstration projects within 30
APWA Reporter
June 2009
The Dominguez Gap Wetlands is a 50-acre constructed wetlands and spreading grounds facility located along the Los Angeles River in Long Beach, California. It opened to the public in May 2008. (Photo by Dave Weilenga)
the comprehensive Los Angeles River Master Plan. The Dominguez Gap Wetlands Project is located adjacent to the Los Angeles River south of Del Amo Boulevard and north of the 405 Freeway in what has historically been known as the Dominguez Gap Spreading Grounds. It consists of two linear basins on each side of the river. The 36-acre East Basin was graded to create alternating deep pools and emergent wetland zones to provide a year-round aquatic habitat for native wetlands and riparian plant species as well as native wildlife. The slopes of the basins were planted with a riparian fringe, transitioning to upland habitat higher on the slopes. This oasis of habi-
tat provides a much-needed respite for both humans and other wildlife in this dense urban environment. The 14acre West Basin provides habitat on its slopes while primarily serving to provide enough groundwater recharge for about 900 families each year. The natural treatment wetland addresses a broad range of contaminants prior to groundwater recharge. Concentrations of common parameters will be reduced at rates similar to those reported from other treatment wetland projects: total nitrogen (40 to 90%), total phosphorus (10 to 90%), total suspended solids (50 to 90% removal), biological oxygen demand (BOD; 50 to 90%); heavy metals (50 to 90%), and fecal coliforms (up to 99%). Treatment performance varies depending upon