The Bowtie Demonstration Project

The Bowtie Demonstration Project: An Urban Wetland Demonstration Project on the LA River The Bowtie Demonstration Project is located along the Los Angeles River on the Taylor Yard G1 Parcel, now known as California's State Parks and Recreations' Bowtie Parcel. The parcel was formally used for railroad operations and is currently a brownfield site. This parcel is part of the 100 Acres Partnership, a larger effort to create 100 acres of contiguous green space along the Los Angeles River. The project lies 400 feet southeast of a severely disadvantaged community census tract and the surrounding communities rank high in being vulnerable to pollution burden. The project involved community engagement efforts during the planning and design process. Local community-based organizations and over 2,000 individuals were engaged through surveys and in-person events to help explore native plant palettes and ways to offer services to people experiencing homelessness in and around the site. Indigenous community members were consulted for their input on design elements, including plant selection, vector control measures, and educational opportunities. Local, state, and federal agencies were consulted and engaged early in the planning and design stages to ensure feasibility of long-term maintenance and integration with surrounding projects along the Los Angeles River. The project will treat dry-weather and partial wet-weather flows originating from a 3,000-acre drainage area that is primarily comprised of urban residential, industrial, and commercial land uses. All dry weather flows and partial wet weather flows will be diverted from a Los Angeles County Flood Control (LACFCD) storm drain year-round, while partial wet weather flows will continue to flow through the LACFCD storm drain and outfall into the Los Angeles River. The project design includes pre-treatment systems and a constructed wetland to remove bacteria and heavy metals. The treated water will be reused on-site for irrigation to support habitat restoration or returned to the storm drain to outfall into the Los Angeles River. The Bowtie Demonstration Project manages stormwater quality while also creating and restoring habitat. We will highlight how this project's success was the result of intentional collaboration between agencies, community members, and consultants reflecting how to harness the opportunities that exist in supplementing traditional stormwater infrastructure with nature-based solutions. Hydrology, Hydraulics, and Water Quality (The Gray) The project includes a diversion structure, a pre-treatment system, conveyance structures, a constructed wetland, a potable water supply pipeline, an irrigation system, landscaping/habitat areas, and park amenities. HydroCalc, a calculator software, was used to perform the design capture volume analysis for an 85th percentile storm and a 50-year, 24-hour storm. The 85th percentile storm was analyzed as part of the pollutant load reduction modelling while the 50-year storm was defined as the design storm in LA County's Hydrology Manual. Urban runoff volume was quantified using flow observations conducted during dry weather at the project site and used to establish an average dry-weather flow rate. Evapotranspiration data was extracted from the California Irrigation Management Information System. LACFCD's Water Surface Pressure Gradient Model was used to confirm that the diversion structure is not anticipated to impact the storm drain. The pre-treatment system is comprised of the diversion structure, a hydrodynamic separator, media filter, and pump station. The pump station is equipped with a 1+1 pump configuration that operates in a fill and draw scheme. Inlet and outlet structures will be constructed to bring water into and out of the lined wetland during dry weather. An unsteady flow, 2-dimensional model of the project was created using HEC-RAS software to simulate the velocity of water and the water surface elevation of the wetland. Water quality samples were collected at the LACFCD storm drain in 2022, testing for temperature, dissolved oxygen, total dissolved solids, conductivity, turbidity, pH, total coliform, and E.Coli. LACFCD's Watershed Management Modeling System was used to estimate the pollutant load reduction capable by the project. Wetland and Park Enhancements (The Green) The constructed wetland and recreational space features are integral to the multi-benefit nature of the project. The project will involve the planting of approximately 50 native plant species, mimicking the native plants that already exist in the LA River watershed. The Nature Conservancy has teamed with Los Angeles-based public agency and non-profit organization collaborative, Seed LA, to develop the plant palette and quantity matrix for the various habitat zones. Plants have been selected to encourage a variety of pollinator species. More than 50% of the project site will be established with native vegetation. The project site will include accessible walking trails, tree canopied seating areas, and green open spaces for the public to enjoy green space near the LA River. The wetland itself will be planted and kept at a relatively steady water depth through the storm drain's dry weather flows. The wetland is comprised of pools and shallow riffles that vary in depth and volume throughout the water's flow path. The pools are graded deeper than the riffles to allow water to be retained longer for settling of metal or sediment particles, and the riffles are present to allow the passage of flow between the wetland pools. Benefits of Presentation This presentation showcases one way that green and gray stormwater management can be combined. The Bowtie Demonstration Project enhances existing gray stormwater infrastructure that conveys stormwater away from where it lands by reclaiming green space for the community and treating that stormwater in a naturalized wetland. This project demonstrates that sustainable ideas can be created alongside existing infrastructure, which benefit both the community members that live with these projects and the regulators that oversee the watershed as a whole. Status of Completion This project is anticipated to have completed 100% design by the time of the conference and to have begun construction in 2024.