Los Angeles River Watershed

Los Angeles River Watershed

The 55-mile long Los Angeles River originates in western San Fernando Valley and flows through the central portion of the city south to San Pedro Bay near Long Beach. The Los Angeles River watershed covers approximately 834 square miles and is bounded, at its headwaters, by the Santa Monica, Santa Susana, and San Gabriel mountains to the north and west. The southern portion of the Watershed captures runoff from urbanized areas surrounding downtown Los Angeles. Jurisdictions in the Watershed include the city of Los Angeles and 42 other cities.

Much of the watershed is highly developed, with residential, open space and agricultural, and commercial/industrial/transportation being the predominant land uses. Overall, the watershed is approximately one-third impervious.

Most portions of the Los Angeles River are completely channelized for flood protection, as are many of its tributaries including Compton Creek, Rio Hondo, Arroyo Seco, and Tujunga Wash. They are fed by a complex underground network of storm drains and a surface network of tributaries. Several dams and reservoirs have been constructed within the watershed for flood control and groundwater recharge. The river’s two soft-bottom reaches consist of a 3.1-mile portion running adjacent to Los Angeles and Glendale known as the Glendale Narrows and a 2.4-mile portion in the Sepulveda Basin recreational area behind the Sepulveda Dam.

The average dry weather flow is 153 cubic feet of water per second. The average wet weather flow is two to three times higher, and even more during large storms.

Water Quality in the Los Angeles River Watershed

The Los Angeles River and selected tributaries are impaired by pollutants (i.e., trash, metals, bacteria, nutrients) mainly because of the Watershed’s large, dense population and the amount of impervious ground surface that prevents large quantities of runoff from infiltrating into the soils. The Total Maximum Daily Loads (or TMDLs) in the Los Angeles River watershed address metals, nutrients, trash and bacteria. Echo Park Lake, a water body found within the Los Angeles River watershed, has TMDLs that address nutrients, pesticides, PCBs and trash. Lincoln Park Lake’s TMDLs address nutrients and trash.

The Los Angeles River watershed’s Enhanced Watershed Management Program (or EWMP) identifies compliance measures for all Los Angeles River TMDLs and other water quality mandates, while maximizing potential benefits of storm water for local water supply. 

Related documents available:

Catch Basins Inserts as Full Capture Devices /a> (284kb)
Technical Report: Assessment of Catch Basin Inserts (2.1mb)
City LA Selected CB Inserts and Opening Screen Covers (248kb)
Technical Report: Assessment Catch Basin Opening Screen Covers (2.1mb)
Trash Generation Study (528kb)
LAR Metals TMDL Implementation Plan 2010 (9.8mb)
LAR EWMP Work Plan (12.9mb)
LAR Draft CIMP (4mb)
Trash TMDL Implementation Strategy and Plan (4.3mb)

Upper LA River Coordinated Integrated Monitoring Program Data (3.4 mb)