Earvin Magic Johnson Park Urban Runoff Water Recycling & Storm Drain Diversion

Los Angeles, CA

PACE designed a unique new system through a collaboration with the Los Angeles County Community Development Commission (CDC) and Los Angeles County Public Works Watershed Division that sustainably creates a new water source for Earvin Magic Johnson Park by capturing urban runoff (dry and wet weather first-flush flows), treating the captured flows to improve water quality, and recycling the water for on-site irrigation use. The treated recycled water is stored within the park’s lakes and enhances the appearance and water quality of the lake system. This system collects, retains, and reuses all of the wet weather first-flush flows of the 375-acre watershed, amounting to approximately 14 acre-feet (4.5 million gallons) of flows from a significant wet weather event.

Urban Runoff Capture and Delivery
An urban runoff diversion structure taps into an existing 84-inch diameter storm drain to divert flows of up to 33 cubic feet per second (cfs) to a new pump station that sends the flows to the park. The diversion structure is comprised of a low-height partition that will prevent dry weather and first-flush wet weather flows from continuing to flow through the storm drain line, and instead diverting these flows into a new 36-inch pipeline for transfer to the diversion pump station. Wet weather flows beyond the first-flush volume will continue to flow down the existing storm drain line. The pump station contains mechanical screening to prevent trash and debris from being discharged downstream to Compton Creek. The diversion pump station has low-flow and high-flow pumps to handle both dry and wet weather flow volumes.

Urban Runoff Treatment Facility
The flows captured from the storm drain line are pumped into a sophisticated treatment facility with ozone, coagulation, circulation, aeration, and water conditioning prior to discharge to the wetlands at the renovated lake system. A pump at the north lake recirculates water to the treatment system in the south lake at approximately 2,500 gallons per minute to maintain high water quality in the lakes. Lake water is also used for irrigation of the entire park, and potable water make-up is minimized by using the new treated stormwater source.

This treatment facility also houses the treatment system for the park’s new spray ground feature. The spray ground is independent of the lake treatment system and uses potable water per Los Angeles County Public Health codes.

Key Features:

• Low Impact Development (LID) application treating 85th percentile (first-flush) storm event and retaining on-site
• Harvesting dry weather flow (72,000 gallons per day on average) for recycling
• Design of stormwater/runoff treatment system including wetlands
• Storm drain diversion structure – structural and hydraulic design
• Trash racks
• Low and high-flow pump station design
• Force main design from diversion structure to treatment facility
• Recirculation pump and piping