The Los Angeles River Watershed

The River in the Elysian Valley

The Los Angeles River is the heart of an 871-square mile watershed. The watershed encompasses the Santa Susanna Mountains to the west, the San Gabriel Mountains to the north and east, and the Santa Monica Mountains and Los Angeles coastal plain to the south.

The Los Angeles River Watershed has diverse patterns of land use. Forest or open space covers the upper half of the watershed, while the remaining watershed is highly urbanized with commercial, industrial, or residential uses. There are 22 lakes within its boundaries. In addition, there are a number of spreading grounds in the watershed including sites at Dominguez Gap, the Headworks, Hansen Dam, Lopez Dam, and Pacoima Dam. The Los Angeles River is hydraulically connected to the San Gabriel River through the Rio Hondo, although this occurs primarily during large storm events.

Many people don't even realize there is a river in Los Angeles. It's usually remembered as the cement channel where two Terminators had a high-speed chase in the movie T2, or the staging ground for a giant ant invasion in Them!. But our river is more than a backdrop for movies and traffic. It is presently a shadow of it's former self, but areas of great beauty still exist.

The Los Angeles River is not like other rivers in the United States. At only 52 miles long, the L.A. River is 45 times shorter than the Mississippi, but drops 795 feet in elevation from the headwaters in the San Fernando Valley to its end in Long Beach. That's 150 feet more than the Mississippi drops in its entire 2350 miles, meaning our river is short but steep.

In times of peak flow, the river carries 183,000 cubic feet of water per second out to the Pacific Ocean (the equivalent of 40 million garden hoses going full blast) - 14 times the flow of NY's Hudson River. The LA River has no "average" flow, varying widely from a bare trickle in drought years to a raging torrent in years of heavy rain.

The Los Angeles River Watershed has impaired water quality in the middle and lower portions of the basin due to runoff from dense clusters of commercial, industrial, residential, and other urban activities. The impairments include pH, ammonia, metals, coliform, trash, algae, oil, pesticides, and volatile organics.

Of course, one of the most different things about the LA River is the fact that much of it is encased in concrete. Confining the river to a concrete channel began in 1938, as an effort to control the devastating floods that periodically swept through the city. It took 30 years and 3.5 million barrels of concrete to channelize the river and its tributaries, and when it was done, it wasn't called a river anymore. It was renamed the Los Angeles River Flood Control Channel.

Take a tour of the Los Angeles River

Headwaters

The headwaters in Canoga Park

The Los Angeles River begins just beyond the Canoga Park High School football field in the San Fernando Valley, at the confluence of Bell Creek and Calabasas Creek, which flow down from the Santa Susana and Santa Monica Mountains. The river flows southeast, joined by Santa Susana, Browns, Dayton, Chatsworth, Limekiln, Wilbur, Aliso, Woodley, Pacoima and Burbank creeks, that drain the mountains ringing the Valley. Historically, much of the water that flowed through the valley seeped into the ground to fill the giant underground aquifer that has supplied water to Los Angeles for over a hundred years. Now, however, the Valley is over 60% hard surfaces and rainwater is directed to stormdrains that empty directly into the river. The river in the west valley is a now a concrete trapezoid channel.

The Valley

The Los Angeles River in the Sepulveda Basin

At the Sepulveda Basin, however, more than three miles of the river are all but undisturbed, allowing the growth of willows, reeds and other vegetation and giving us a glimpse of the natural river. The Sepulveda Basin is a dry reservoir, a 2.25-square mile emergency flood-control feature behind a 57-foot earthen dam. Although much of this basin is used for recreation, with soccer, baseball, and playing fields, where the soft bottom channel of the river flows, mulefat, sagebrush, willow, and reeds cover the banks. Tributaries joining the river in the Basin are Bull Creek, Hayevnhurst Creek and Haskell Creek. Along Haskell Creek is a 225-acre Wildlife Reserve that serves as protected habitat for hundreds of species. From the Sepulveda Basin, the river flows as a concrete box channel east through the San Fernando Valley.

Big Tujunga Wash drains the northwestern San Gabriel Mountains. Starting high in the Angeles National Forest and running wild until it encounters Hansen Dam in Sun Valley, it then becomes a concrete box channel. As it continues through the eastern San Fernando Valley, it joins with the Pacoima Wash, then meets the Los Angeles River at the CBS studios in Studio City. As the river continues east past the studios, it is joined by the Burbank Wash and the Verdugo Wash in Glendale.

Downtown

the transition from concrete to soft bottom

The river widens and turns south around Griffith Park, and heads through what is known as the Glendale Narrows - a rocky bottleneck that forces any underground water to the surface to join the visible river. Here begins the soft-bottom portion of the river referred to as the Elysian Valley, another eight miles of river lush with islands of trees, brush and reeds, and a favorite haunt of birds on the Pacific Flyway. Below the Elysian Valley is the confluence of the Arroyo Seco and the Los Angeles River.

The Arroyo Seco drains the southwestern section of the San Gabriel Mountains. Starting high in the San Gabriel Mountains and running through Pasadena near the Rose Bowl, it continues through South Pasadena to meet the LA River just north of Downtown Los Angeles.

After the confluence the Los Angeles River becomes a fully concrete trapezoid channel and is spanned by architecturally historic bridges that carry automobiles full of people - who rarely realize they are crossing the Los Angeles River. To preserve these bridges, the riverbed was lowered and piers of the bridges enhanced and strengthened so that the river could be clad in concrete!

Southern Cities & the Estuary

The estuary and Queen Mary at Long Beach

South of the City of Los Angeles, the river flows through the cities of Vernon, Maywood, Bell, Bell Gardens, Cudahy, Southgate, Lynwood, Compton, Paramount and Carson on its way to Long Beach. The Rio Hondo joins the Los Angeles River at Southgate from the east, connecting it to the San Gabriel River. The last tributary mingling with the Los Angeles River is Compton Creek. South of Compton Creek, the river flows down between a concrete or rock channel into the estuary in Long Beach, right by the Queen Mary. The last several miles of the river are soft-bottom and lined with rock riprap, and are a favorite spot for shorebirds.