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 (33%), 42 other cities (29%), and eight agencies (37%).

Much of the Watershed is highly developed, with residential (36%), open space and agricultural (44%), and commercial/industrial/transportation (20%) 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 at the Watershed’s most downstream monitoring station near Long Beach is 153 cubic feet per second. The average wet weather flow is two three times higher, or even more during large storms.

Water Quality in the Los Angeles River Watershed

As of March 2012, the USEPA has approved 22 TMDLs throughout the region that list the City of Los Angeles as a responsible jurisdiction. These include waterbodies within the Los Angeles River, Ballona Creek, Santa Monica Bay, and Dominguez Channel Watersheds.

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. Currently there are several TMDLs that are in the Watershed, including:

  • Los Angeles River Metals TMDL
  • Los Angeles River Nutrients TMDL
  • Los Angeles River Trash TMDL
  • Los Angeles River Bacteria TMDL
  • Echo Park Lake TMDL (nutrients, pesticides, PCBs, trash)
  • Lincoln Park Lake TMDL (nutrients, trash)

The City with other agencies in the Los Angeles River watershed is currently developing an Enhanced Watershed Management Program (EWMP). The EWMP will identify the measures for compliance with all Los Angeles River TMDLs and other water quality mandates, while maximizing potential benefits of stormwater for local water supply. The draft EWMP will be available by June 2015 and be finalized by April 2016 after review by the Regional Water Quality Control Board.

Projects throughout the watershed are improving water quality by reducing the amount of pollution flowing into rivers and creeks that drain into the Los Angeles River.

What is a TMDL?
A Total Maximum Daily Load (TMDL) is the maximum amount of a specific pollutant, such as trash, bacteria, or pesticides that could be discharged into a waterbody without causing it to become impaired. Development of TMDLs, which are driven by the Clean Water Act, are an important step in cleaning up our creeks, lakes, rivers, and beaches.

Related PDF documents available for download

Catch Basins Inserts as Full Capture Devices 2006 (284kb)
Technical Accessment Catch Basin Inserts 2006 (2.1mb)
City LA Selected CB Inserts and Opening Screen Covers 2006 (248kb)
Tecnical Accessment Catch Basin Opening Screen Covers 2006 (2.1mb)
Trash Generation Study 2002 (528kb)
LAR Metals TMDL Implementation Plan 2010 (9.8mb)
LAR EWMP Work Plan 2014 (12.9mb)
LAR Draft CIMP 2014 (4mb)
Trash TMDL Implementation Strategy and Plan 2006 (4.3mb)