Hollenbeck Park Lake Rehabilitation and Stormwater Management
The purpose of the presentation is to share the details of an innovative multi-benefit project in the LA River watershed. The project will improve water quality and control algae at an urban lake and contribute to water quality improvement in the watershed, replace potable water with a combination of recycled water and dry/wet weather runoff, and restore the park’s appearance and function for recreational uses.
Hollenbeck Park has provided the City of Los Angeles and the community of Boyle Heights aesthetic and recreational public uses for over 100 years. The Park is oriented around Hollenbeck Park Lake (HPL), a 4.3-acre manmade urban waterbody that serves as an attractive water feature for public enjoyment. HPL has a history of water quality concerns attributable to excessive nutrient and sediment loading. HPL also exhibits extensive erosion around its perimeter. The City of Los Angeles Bureau of Sanitation (LASAN) is proposing to implement water quality improvements at HPL, replace potable water with dry/wet weather flow and recycled water, restore Hollenbeck Park’s appearance, and provide a long-term solution to erosion around the lake’s edge.
The proposed project includes the following key components:
- Floating Wetland Islands (FWIs). FWIs have been shown to help control algae through competition for nutrients, enhanced settling of algal cells, and water column shading. Five FWIs were installed in 2015 with three additional FWIs to be installed later this year.
- Aeration. Aeration is anticipated to improve water clarity through reduction in algal populations, assist with nitrogen transformation by nitrification, and enhance decomposition of organic sediments.
- Chemical Feed System Retrofit. Alum injection will reduce phosphorus concentrations, thereby reducing algal populations and enhancing solids settling.
- Recycled Water. Recycled water will replace potable water for irrigation and lake replenishment. The use of recycled water for lake replenishment will require additional treatment through shoreline wetlands.
- Dry/Wet Weather Flow Diversion. Dry weather flows and a portion of storm flows will be diverted and treated by the shoreline wetlands.
- Processing. Water from HPL will be filtered and disinfected before distribution to the irrigation system.
- Shoreline Wetlands. Shoreline wetlands will provide passive improvement of water quality through a two-stage process to create an ecological habitat. The new water supply (recycled water and dry/wet weather flow) will be routed to the shoreline wetlands, where water is distributed through a gravel filter situated under a new pedestrian-friendly sidewalk, and discharged into a constructed shoreline wetland for final polishing before inflow to the lake.
- Dewatering/Dredging. Dredging of existing lake sediments will significantly improve water quality. Dredging can be performed using mechanical methods after the lake has been drained.
- Lining. A geosynthetic liner will eliminate seepage and significantly reduce water demands.
Audience members can apply features from this project that integrates innovative stormwater management with multiple benefits: improving water quality in the lake and surrounding watershed, replacing potable water with a sustainable water supply, and providing recreational benefits.
The speakers will encourage questions and interaction with the audience during the presentation. Also, the presentation will include several color photos and artistic renderings showing design concepts, flow schematics, and landscaping and architectural graphics.
The presentation speaks directly to the conference theme: “CASQA in the Capital: Building Bridges for Water.” The project addresses the broader issues of water management by using alternative sources to replace potable water and improving water quality within the lake and watershed using innovative wetland and other treatment approaches.
Wilfred Hsu is a civil engineer and senior project manager with CH2M. He has 20 years of experience in the environmental consulting industry helping clients better manage stormwater. He has extensive experience in the preparation of stormwater management plans, stormwater quality analysis, BMP design, TMDL implementation, and NPDES compliance.