Five Low Flow Diversions on Arroyo Seco and LA River

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The results from the ongoing stormwater quality monitoring program, led by the City of Los Angeles LASAN, identified high bacteria levels in dry-weather discharge to the Arroyo Seco and Los Angeles River. In order to meet the mandated Total Maximum Daily Load (TMDL) regulations, the LASAN and Bureau of Engineering (LABOE) proposed five Low Flow Diversion (LFD) systems: two DWD systems to divert dry weather flow from the Arroyo Seco (AS), and three LFD systems to divert dry weather flow from the Los Angeles River, Reach 2 (R2). These LFD systems will divert dry weather flow from the prioritized stormwater outfalls to sanitary sewers for treatment at the Hyperion Water Reclamation Plant (HWRP). The LFD systems consist of storm drain diversion structures with weirs and pipelines, trash collection maintenance holes, pump stations, discharge pipes, pressurized pipes, valve and meter vaults, power supplies for pump stations, a Supervisory Control and Data Acquisition (SCADA) system, and instrumentation.
 

Arroyo Seco Low Flow Diversion (Sycamore Grove Park, LFD#1, AS-15)


The AS-15 LFD is located at Sycamore Grove Park. The LFD diverts dry-weather flows from a City-owned storm drain which runs perpendicular to the Arroyo Seco Parkway. The LFD collects dry-weather runoff from approximately 1,135 acres of the Arroyo Seco watershed. The Project diverts 100 percent of dry weather flows at this outfall location.

Arroyo Seco Low Flow Diversion (Hermon Dog Park, LFD#2, AS-21)


The AS-21 LFD will be located at Hermon Dog Park. It diverts dry-weather flows from a City-owned storm drain which runs through Hermon Dog Park to a sewer line in Via Marisol (drainage area is 266 acres).

LA River LFD (Palmetto, LFD#1, R2-J)


Dry-weather flow from a County-owned storm drain at 2nd Street and Rose Ave. is intercepted by the installation of a diversion weir and drop inlet. The diverted flow is conveyed via gravity flow to a trash collection manhole, which is then pumped to a valve vault to continue gravity flow to the existing sewer main in Alameda street. The Project collects flows from a 1,710-drainage area.

LA River LFD (Mission Rd, LFD#2, R2-G)


Dry-weather flow from two perpendicular City-owned storm drains in Palmetto Street and Santa Fe Avenue is intercepted by the installation of diversion wells and drop inlets. The diversion flow is conveyed via gravity to a trash collection manhole, which then will be pumped to a valve vault to continue to the sewer. The Project collects flows from a 169-acre drainage area.

LA River LFD (2nd St & Rose LFD#3, R2-02)


Dry-weather flow from a parallel City-owned storm drain in Elliot street is intercepted by the installation of diversion weir and drop inlet. The diverted flow is conveyed via gravity to a trash collection manhole, which is sent to the sanitary sewer located at the intersection of the US 101 freeway and Mission Road. The Project collects flows from a 2,490-acre drainage area.

Project Goals and Benefits


Construction of these LFD systems will divert dry weather flow from the prioritized stormwater outfalls to sanitary sewers for treatment at the Hyperion Water Reclamation Plant (HWRP) will help meet the mandated Total Maximum Daily Load (TMDL) regulations, prevent and reduce the high bacteria levels in dry-weather discharge to the Arroyo Seco and Los Angeles River, and provide water supply and recycling benefits for the City.

Project Funding


The project is funded by the Los Angeles County Safe Clean Water Program.

If you’d like to receive additional information, please contact san.safecleanwater@lacity.org and place “Five Low Flow Diversions on Arroyo Seco and LA River” in the subject line.

To learn more about the projects funded by the Los Angeles County Safe Clean Water Program, please visit LA County’s Safe Clean Water Program’s project map.