Model for Urban Stormwater Treatment

September 2014 » Exclusive
South Los Angeles Wetland Park sets the standard for achievement in sustainability.
Sean P. Vargas, P.E., ENV SP, LEED AP
The South Los Angeles Wetland Park is helping transform a community by turning a former brownfield site into a rare public park space in a highly urbanized setting.

The South Los Angeles Wetland Park demonstrates a bold, integrated, and sustainably engineered project approach that captures and treats urban runoff, while at the same time creating a new neighborhood-rejuvenating amenity. The project is helping to transform a community by turning a former brownfield site into a rare public park space in a highly urbanized setting. By revitalizing a neighborhood while treating urban runoff, the 10-acre park earned the Envision Platinum award — the highest level attainable in the Institute for Sustainable Infrastructure (ISI) rating system.

The South Los Angeles Wetland Park is in a historically underserved area of Los Angeles County formerly known as South Central Los Angeles. Completed in 2013, the $7.84 million project was conceived to protect public health and meet Federal Clean Water Act requirements. It is located within the Los Angeles River Watershed, a highly urbanized area tributary to the Los Angeles River (a largely concrete-paved channel discharging to the Pacific Ocean).

Psomas served as the prime consultant and designer on the project, a centerpiece of the city’s $500 million Proposition O Clean Stormwater Bond program.

Proposition O projects help to protect public health by preventing polluted discharges to the city’s watercourses, beaches, and the Pacific Ocean in order to satisfy Clean Water Act requirements. The program established a framework within which environmentally, socially, and economically sustainable projects could rate highly and ultimately receive funding. Projects considered for funding were grouped into A, B, and C categories based on the extent that they satisfied the bond act’s criteria. The South Los Angeles Wetland Park was one of the first Category A projects.

Improved quality of life has resulted from the project as community members enjoy nature while strolling, jogging, and walking their dogs in a nature park right in their midst.

Multi-benefit project

To reflect and amplify the multi-benefit mandate established for the project, the park needed to act as a local neighborhood-serving amenity, provide a profound environmental benefit, and represent a catalytic “node” in the revitalization of South Los Angeles.

A key metric with respect to social sustainability is the degree to which a project respects or, preferably, restores important community assets. The project has helped to energize the host and nearby communities. Genuine collaboration with the community has elevated awareness and pride. A markedly improved quality of life has resulted as community members enjoy nature while strolling, jogging, and walking their dogs in a nature park right in their midst.

Community-engaging park features include:

  • an outdoor classroom amphitheater;
  • an educational kiosk and signage describing the park’s function, flora, and fauna;
  • a recreational walking trail around the treatment wetland;
  • picnic areas with benches; and
  • observation bridges and platforms overlooking the wetland.

Treating regional urban runoff

The treatment wetland reduces the introduction of pollutants generated from urban runoff to receiving waters via a series of stormwater Best Management Practices. Project BMPs include a combination of structural and green elements within the treatment train.

The treatment train begins below ground at an existing 63-inch storm drain mainline, which serves the contributing sub-watershed. A new, low-head-loss, drop-type diversion structure was constructed to divert urban runoff for treatment and beneficial use within the new wetland.

Structural pretreatment is provided to prevent clogging of the wetland’s pump system and the transport of trash, debris, grit, and grease into the wetland itself. Structural pretreatment elements downstream of the diversion include a trash rack/bar screen and a hydrodynamic separator. After pretreatment, runoff enters centrally monitored (SCADA) pump sections that are designed to operate within two distinctly different inflow regimes:

Dry season — During the dry season all urban runoff from the 525-acre sub-watershed is captured, treated, and used to sustain the treatment wetland and offset evapotranspiration-related losses.

Wet season — During the wet season precipitation-related runoff is diverted to the forebay via a submerged energy dissipater to minimize scour, suspended solids transport, and re-entrainment. After the maximum treatment volume is reached, redundant ultrasonic/float level controls in the wetland de-energize the pump system while the wet weather event-related treatment volume is slowly discharged.

Envision rating process

The ISI Envision rating system provides a holistic framework for evaluating the community, environmental, and economic benefits of infrastructure projects. It recognizes projects that use this transformational, collaborative approach to assess project sustainability factors.

In February 2013, Psomas met with the Los Angeles Bureau of Engineering to formally kick off the Envision process for the South Los Angeles Wetland Park. This decision was based on the client’s and consultant’s mutual commitment to sustainability and their desire to partner to learn about Envision’s benefits.

When Psomas began the formal Envision assessment process, the project was already under construction. This made the process somewhat of a forensic exercise, since many decisions about project development and design had already been made. Certainly the effort to prepare and compile credit-supporting documentation would have been easier if it had occurred during the normal course of design, rather than during construction.

The assessment process was facilitated by the fact that the project director, an ISI/Envision trained verifier, was the designated Envision sustainability professional (ENV SP) for the project. This helped the team understand what to look for and where to look for it, in terms of specific credit-supporting documentation.

The project reduced energy consumption by 77 percent through the installation of solar lighting.
The treatment wetland reduces the introduction of pollutants generated from urban runoff to receiving waters via a series of stormwater Best Management Practices.

Features of the project that helped it score highly within the Envision framework included remediation of the former brownfield site, creation of new urban green space, and the park’s use of urban runoff as a treatment-wetland sustaining resource. The park ranked very highly in a number of specific credit areas including:

Quality of Life — The former industrial site previously was inaccessible to the public, unsightly, and surrounded by an 8-foot chain link fence. The project enhanced public space and restored site accessibility. Being surrounded by homes and schools, the site made an ideal locale for an urban park featuring restored natural features and green space.

Leadership — The project showcased effective leadership and commitment of all involved parties. It improved the infrastructure integration of the regional storm drain system by using water from the storm drain network to sustain the wetland. It featured a series of stormwater BMPs to regionally treat urban runoff from a 525-acre contributing watershed, in addition to adding beneficial park space in the community.

Resource Allocation — The project reduced energy consumption by 77 percent through the installation of solar lighting. An extensive initial commissioning of the pump stations was conducted to ensure the SCADA system controlling the wetland’s low-flow and high-flow pump systems operated efficiently.

Natural World — As noted above, the project transformed the previous brownfield site into an urban park with numerous amenities. A wetland with riparian and emergent marsh habitat was created at the center of a densely populated urban community. These open-water, emergent marsh, riparian, and upland plants contribute to wetland habitat restoration and help restore species biodiversity.

Climate and Risk — The project was designed to be resilient and adaptive to the consequences of long-term climate change scenarios, such as extreme flood or drought.

Appreciated by a broad audience

The City of Los Angeles’ commitment to sustainability, paired with the Proposition O ranking criteria that favored multi-benefit projects, created an atmosphere that allowed for progressive solutions in creating the South Los Angeles Wetland Park. An extensive pre-design process promoted study and development of project features that exemplify the triple bottom line that Envision promotes.

The exposure that the project has received as a result of the Envision Platinum award has allowed the merits of sustainably engineered infrastructure to be understood and appreciated by a broader audience. The park has been honored with the Superior Achievement Award by the American Academy of Environmental Engineers & Scientists and a National Recognition Award from the American Council of Engineering Companies.

Sean P. Vargas, P.E., ENV SP, LEED AP, is Psomas’ director of sustainability. He served as project director for the South Los Angeles Wetland Park, as well as the ENV SP for the project.


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