Cleansing stormwater and creating parkland in LA’s urban core
As published by Land and Water Magazine
By Sean P. Vargas PE, ENV SP, LEED AP BD+C
A wetland park is emerging in the heart of South Los Angeles, transforming a former rail-transit yard into precious urban green space.
Yet at the same time the community is gaining precious green space and a natural oasis, a newly constructed wetland will capture and treat polluted stormwater runoff from a 525-acre watershed before releasing it into the Pacific Ocean.
Approved unanimously by the Los Angeles City Council in April 2008, the $14 million South Los Angeles Wetland Park is especially unique because it is in the heart of an economically disadvantaged community with a scarcity of parkland or opportunities to get in touch with nature.
Los Angeles City Councilwoman Jan Perry has long eyed the site, which sits in her district. Owned by the Metropolitan Transit Authority (MTA), the property was a former maintenance yard for buses and trolleys dating back to 1901. The paved nine-acre parcel, sprawling a full city block, was encircled by rusted chain-link fencing and razor wire. “Pretty blighted,” in Perry’s words.
The lot was “a barren, underutilized concrete pad,” Councilwoman Perry said in an interview with the Los Angeles Times. But she saw the potential. Surrounded by homes and schools, the site would make an ideal locale for an urban park.
The city’s Bureau of Sanitation joined Perry in seeing the potential of the site. The Bureau saw the opportunity to capture stormwater and use it as a resource, part of the city‘s focus on green solutions to deal with polluted stormwater. Wetlands can accomplish this goal, at the same time creating a community amenity.
Through a multi-agency partnership, the plan to create a major stormwater best management practice (BMP) and parkland in the heart of the city began to take shape.
The momentum for the wetland park accelerated in 2004 when voters in Los Angeles overwhelmingly passed Proposition O. Proposition O authorized the city to issue $500 million in general obligation bonds for stormwater programs to meet Federal Clean Water Act requirements.
The resulting program of stormwater quality improvement projects is setting a national standard for stormwater quality solutions within a built-out urban watershed. The city is creating a template for a highly effective BMP program for urban areas near lakes, rivers, streams, and oceans that need protection from polluted stormwater runoff. Treatment through BMPs like the wetland park is helping the city meet Total Maximum Daily Load requirements set by the Regional Water Quality Control Board for the Los Angeles River Watershed.
The success of Proposition O was due in large part to the city’s decade-long public education effort on water quality issues. Once the bond measure was approved, city officials involved stakeholders at every level—from project selection to implementation. Members of a Citizens Oversight Advisory Committee were appointed by the Mayor and City Council based on their expertise and experience with clean water issues.
The Bureau of Engineering requested project ideas from the public. Dozens of proposals were submitted, reflecting a wide range of detail and completeness. Some were quite rudimentary; others were prepared by consultants.
The most promising submittals were fleshed out to 15- to 20-page Concept Reports with more detail, graphics, and supporting documentation. One of the high profile projects that made it through the public stakeholder process early and one of the first to be funded was the South Los Angeles Wetland Park.
Proposition O was the funding catalyst and without it, getting this project off the ground would have been an uphill battle. In addition to $8 million in Proposition O funds, the project is receiving $900,000 from MTA for site remediation as well as funding from other propositions for park improvements, drinking water supplies and natural resource protection.
The project is multi-phased to comply with grant funding requirements with the first phase opening in late 2010/early 2011 and the final phase set to open in late 2011.
Psomas is the prime consultant for the implementation of a number of City of Los Angeles’ Proposition O projects. After approval by the Citizens’ Oversight Committee, Psomas was brought in by the city to initiate pre-design work. With extensive experience in bond-funded sustainability programs, Psomas could step in seamlessly and act as an extension of the city for stormwater-related projects.
A primary goal of the South Los Angeles Wetland Park is to minimize pollutants in urban runoff by diverting flow through a 4.5-acre treatment wetland prior to release back into the stormwater conveyance system. This is a departure from the legacy urban flood control approach of draining watersheds into paved channels/storm drains and discharging directly into receiving waters without treatment.
The diversion and treatment system consists of the following features: a stormwater diversion structure to divert water from the storm drain, screening, computer controlled low-flow and high-flow pump sections, stormwater pretreatment, force main and distribution, a three-cell constructed treatment wetland, and overflow/return structure.
The treatment wetland itself is unique in that it will be located in Los Angeles’ subtropical climate which receives little to no precipitation for seven months out of the year. The wetland was designed to treat runoff as well as be sustained from the same source—the existing 60” storm drain adjacent to the project site.
Dry Weather Runoff
The concept of dry weather runoff is somewhat esoteric. The layperson tends to think that “if it isn’t raining there isn’t any runoff.” To the contrary, dry weather runoff is quite common and widespread. It is the result of many activities within a watershed, from irrigation overspray to car washing to leaking pipes. Capturing and treating dry weather runoff in a dry climate like Los Angeles is particularly important. The nature and relative concentration of the pollutants in this type of runoff are different than the characteristics of pollutants in both wet weather runoff and even dry weather runoff from climates that receive regular precipitation.
On-site flow monitoring performed in September 2007 (a very dry year) showed an average available daily baseflow of approx 14,000 gallons per day in the adjacent storm drain. Since a wetland of this nature needs to be wet all year, detailed water-balance computations were performed to help size the wetland so that it will be sustained by dry weather runoff during extended dry periods. 100% of the dry weather runoff will be diverted from the storm drain and treated by the wetland.
Wet Weather Runoff
Wet weather runoff, or runoff from precipitation, is commonly understood. During a storm event, the high-flow pump section will rapidly fill the wetland to its more than two acre-feet treatment volume capacity, at which point the monitoring and control system will shut down the pumps to prevent wash out and allow treatment and slow discharge to occur.
An Urban Oasis
Visitors to the wetland park will enjoy educational opportunities and wildlife viewing, trails, picnic areas, and a multi-use community center. The park will feature historical railway elements, along with the reutilization of a historical building. The wetlands will include a small lake, marshes with native plants, footpaths, and a winding waterway.
Irrigation requirements will be minimal for the park. Upland areas will be landscaped with native high-desert type vegetation that will need about a third of the irrigation that would normally be required by a public park with lawns.
Post -construction maintenance and monitoring will be split between the Recreation and Parks Department and the Bureau of Sanitation.
A project of this complexity and magnitude is not without its challenges. In addition to the complex funding issues outlined above, challenges ranged from managing the brownfield cleanup and excavation of a historical site to coordination with multiple agencies.
- Brownfield cleanup. Exhaustive pre-design report work was done to learn as much about the site as possible to minimize unforeseen conditions. Historic site conditions stemming from its use as a maintenance yard for buses and trolleys dating back to 1901 proved a great challenge, precipitating a number of requirements.
- Unforeseen Conditions: An archeologist was needed on site to photograph and document buried rail spurs due to their historical significance.
- Partnership and Interagency Coordination: Numerous agencies were involved in this effort, including the Bureau of Engineering, Bureau of Sanitation, Department of Building and Safety, Recreation and Parks Department, the MTA, Council Office, state and federal agencies, as well as public stakeholders.
As yet no major issues have surfaced during construction. This is largely due to the rigorous vetting process prior to groundbreaking—concept reports, pre-design reports, and highly detailed design documents—more attention than many projects get.
A Model for Urban Watersheds
The South Los Angeles Wetland project clearly demonstrates how our urban planning visioning has matured. It has provided the unique opportunity to create much-needed park and greenspace in an inner city community, while at the same time protecting our waterways from stormwater pollution. What is the ultimate lesson learned? Through innovation and partnership a project of this nature is achievable and can be re-created in urban watersheds across the country.
Sean Vargas is Psomas Vice President and Program Director for all Psomas Proposition O projects.