South Los Angeles Wetland Park

Challenge

The designers were challenged to create a stormwater quality improvement project which required at least a 4-acre water body as part of the California Environmental Quality Act (CEQA). It also had to function as a park on a flat, inland site that lacked a natural water system.

Solution

The design solution was a constructed wetland with an integrated park. By redirecting stormwater from grey infrastructure below to the surface, the design created a visual amenity while simultaneously cleaning water from a 525-acre sewershed in South Los Angeles. 

• 4.5 acres of wetlands and 4.5 acres of upland habitat were created on site. 40 species of open-water, emergent marsh, riparian, and upland plants were selected to withstand both flooding and drought. Wetland plant species include sandbar willows (Salix exigua), California bulrush (Schoenoplectus californicus), tall flatsedge (Cyperus eragrostis) and yerba mansa (Anemopsis californica). Upland species include California rose (Rosa californica), hummingbird sage (Salvia spathacea), mulefat (Baccharis salicifolia), and coast live oak (Quercus agrifolia). 
• Stormwater runoff is collected in the northwest corner of the site, diverted to an underground pretreatment system, and then circulated through the constructed wetland. Any excess, now treated, water is delivered back to the traditional stormwater system at the western side of the site.
• A pretreatment hydrodynamic separator removes sediment, trash, oil, grease, gasoline, and heavy metals before urban runoff enters the natural system. During the wet season, precipitation runoff from the traditional storm sewer system enters the forebay, which minimizes scour, helps suspend solids, and facilitates the water entering the wetland system. Once the forebay reaches capacity, water from the storm sewer stops being pumped into the system while the contained water is slowly discharged into the wetland.
• The wetland pools are designed to maintain a depth greater than 5 ft, which helps encourage water flow, enhances wind-driven oxygenation of the water, limits colonization of emergent vegetation, allows particulate matter to settle, and discourage mosquito reproduction. Exposure to UV light from the sun helps reduce the bacteria in the stormwater as it moves through the wetland system.
• A vegetated swale containing Western sycamores (Platanus racemosa), holly-leafed cherry (Prunus ilicifolia) and deer grass (Muhlenbergia rigens) directs runoff from the parking area into the wetland.
• 41 solar-powered LED lights provide overhead light on the trails and in the parking lots. Solar panels are affixed to the top of the light pole and store extra energy in gel cell batteries.
• A 0.5-mile recreation trail made of 65,000 sf of decomposed granite along the filtration ponds provides a place for park visitors to jog or walk.
• Educational signage teaches park visitors about the different types of planting zones as well as how water moves through the site and is cleaned. The signage is an educational opportunity for the high school across the street and adjacent elementary school.
• The Paint Shop Building, a historically significant structure, was preserved as part of this project with plans to reuse it in Phase II. The building was the first building in the western United States to be constructed with concrete, tilt-up wall construction. It is the sole building known to have been constructed in California by Robert H. Aiken, an influential and important innovator in concrete construction.

The South Los Angeles Wetlands Park was first envisioned and funded as a water quality improvement project. It was conceived under Proposition O, an initiative passed by Los Angeles voters in 2004 with the explicit purpose of improving the quality of the region’s waters by preventing water pollution and removing contaminants from waterways. In 1998, a local environmental group, Santa Monica Baykeeper, sued the City of Los Angeles and was joined by others including the Environmental Protection Agency, the Los Angeles Regional Water Control Board, and various community groups. In late 2002, a judge found the city liable for violating the Clean Water Act, and the following April the city accepted liability for more than 3,670 sewage spills in the previous decade. As part of the agreement, Los Angeles committed to replacing 488 miles of sewer lines and cleaning 2,800 miles of sewer infrastructure annually, allocating $2 billion to maintain and repair the system over 10 years, as well as spending $8.5 million on creek and wetland restoration projects. That same year, district councilwoman Jan Perry proposed a wetland park for the highly urbanized neighborhood of Council District 9 to help address water quality issues. By facing these challenges, the city avoided future lawsuits and penalties of unknown size; however, the original lawsuit brought a requested $550 million in damages against the city.

• All educational signage is in English, despite the park’s location in a neighborhood with a high Latino population. The project team developed informative wayfinding and educational signage that was placed at the entrance of the park. However, the only signs in Spanish are regulation-oriented such as “no trespassing.”  
• Extreme weather and climate change impacts should be considered during the design process of any project. Although the park was conceived as a wetland, due to the extremely low water flows (especially during extended periods of drought), this was in reality never possible. Without supplemental water, the wetland would dry up during the summer months, which was not acceptable to project advocates. Since it was expected even in early phases that the required base stormwater flow of 14,000 gallons per day could not be sustained during dry summer months and that additional water would have to be added to the wetland system, the park was designed so that potable water could be pumped into the site and circulated throughout. While the required amount of supplemental water was predicted to be 720,000 gallons per year, due to the extended drought, between 2012 and 2014 an average of 10.8 million gallons of supplemental water was needed, costing an average of $38,600 per year.
• Because the site was designed with the primary goal of water treatment, the wetland system occupies much of the land area. Although 88 trees were planted along the wetland’s periphery, park users have commented on the general lack of shade, which has a negative impact on park usage during Southern California’s hot summers. Incorporating more shade, whether from additional trees or with a structure, would likely increase community use of the park.
• The project was divided into 2 phases, with Phase I being the construction of the wetland, natural, and park spaces and the second one being the adaptive reuse of the existing building on site. This building was intended to house an interpretive museum and community space as well as restrooms. However, due to funding issues, Phase II has not been completed. This has left the park without bathrooms for park users. Incorporating bathroom facilities into Phase I or confirming secured funding for Phase II would have prevented this.
• One of the project goals was that the park would become a educational asset for nearby schools. Interviews with school administrators from two nearby high schools, one middle school, and one elementary school revealed that the park has not been used for formal educational activities. This is a missed opportunity, since the wetland provides a novel environment for learning.

Geosynthetic Clay Liner: Cetco, Bentomat SDN, GSE Bentoliner NWL
Solar Light Fixtures: SOL, Inc.
Drinking Fountain: Haws
Trash Receptacles: Forms and Surfaces
Irrigation: Rainbird
Irrigation Controller: Smart Controls, LLC
Hydrodynamic Separator: CDS Technologies from Contech
Trash Receptacles: Forms + Surfaces
Picnic Table and Bench: Quick Crete Products Corp.
Plants: Recon Native Plants, Norman’s Nursery
Boulders: Tropical Creations, Inc.
Pump Station Fabrication: U.S.F. Fabrication, Inc.
Aerating Fountain: Otterbine Barebo, Inc.
Water Pumps: HOMA Pump

Project Team

Client: City of Los Angeles
Civil Engineering and Survey: Psomas
Landscape Architect: Mia Lehrer + Associates
Structural Engineer: JCE Structural Engineering, Inc.
Mechanical, Electrical, Instrumentations and Controls: Lee & Ro, Inc.
Geotechnical Engineer: Ninyo & Moore
General Contractor: Ford E.C. Inc.
Wetland Ecology Management and Implementation: EcoKai
Wetland Ecologist: Dr. Edith Read
Lighting Design: South Coast Lighting and Design
Water Pump Consultant: Weiland Aquatronics

Role of the Landscape Architect

An engineering firm was the lead for the project. They subcontracted the landscape architect for the user-level site design and planting plan, which connects the natural system to the community, allowing the park to function not only for natural water cleansing, but also as a recreational asset for the surrounding community.