The Bay and its Watershed

The Santa Monica Bay Restoration Project (SMBRP) is mainly concerned with improving Bay water quality and enhancing the Bay's overall health. To accomplish these goals, it is critical to have a full understanding of the entire Bay watershed, and how water eventually arrives in the Bay.

The story of Southern California is the story of water. Because we live-as Marc Reiser notes in his book Cadillac Desert-in a "desert masquerading as a semi-arid ecosystem," we depend upon imported water to help this area sustain its sizable human population.

We have come a long way from 1781, when the first European settlers founded Los Angeles Pueblo on the banks of the Los Angeles River and diverted its water through zanjas, ditches that carried water for crops and drinking. Befitting its size and population, the Los Angeles basin now has one of the most complex water supply and delivery systems of any major city in the world.

Where does our water come from?

Only 15 percent of the city's water supply comes from natural aquifers. An aquifer is an underground bed or layer of earth, gravel, or porous stone that stores and yields water. The largest local aquifer is the San Fernando Valley Groundwater Basin, which holds enough water to supply a million people for two years. It is replenished, as is all groundwater, primarily by periodic rains. Given the small average yearly rainfall in this area (6 to 24 inches), Los Angeles has had to build aqueducts to fuel its growth. Some 75 percent of the city's water supply, on average, is imported through two major aqueducts.

The older Los Angeles Aqueduct, completed in 1913 and extended in 1940, carries water 338 miles through gravity-powered pipelines and ditches from the Owens Valley in the eastern Sierras. (Incidentally, a fictional depiction of the city's wresting of this water from the Owens Valley forms the backdrop for screenwriter Robert Towne's Academy Award-winning movie, Chinatown.)

The new Los Angeles Aqueduct, completed in 1970, also taps the eastern Sierra watershed, and increased the city's water supply by fifty percent. Both aqueducts are managed by the city's Department of Water and Power (DWP).

In addition, the city buys ten percent of its water from the local Metropolitan Water District (MWD), a consortium of Los Angeles and 14 other local cities, 12 municipal water authorities, and a county water authority. The MWD serves more than 130 cities and many unincorporated areas in southern California. MWD imports water both from the Colorado River through a 300-mile long aqueduct, and through the equally massive State Water Project. The latter aqueduct conveys water from Northern to Southern California through a canal that begins in the Sacramento Delta.

How is our water treated?

When the water arrives in the area, it is filtered and treated for possible contaminants at three treatment plants. The two largest facilities are the MWD's Jensen Filtration Plant and the DWP's L.A. Aqueduct Filtration Plant, both in the northern San Fernando Valley.

Two other treatment plants of note, both in North Hollywood, treat underground water that has been contaminated with trace amounts of industrial solvents, most of which seeped into the ground and percolated to the aquifer from WWII munitions and defense industry facilities.

Where does our water go?

Whatever its initial source, after the water is used, most of it finds its way through the region's sewers or storm drains to the Santa Monica or San Pedro Bays. Only that water that passes through sewers receives any kind of treatment-storm drains lead straight to the ocean, and the waters that flow through them are not treated.

Only a small portion of the millions of gallons per day that passes into either Bay is diverted or reclaimed.

The DWP operates two major water reclamation plants, the Los Angeles Glendale Water Reclamation Plant, which produces 20 million gallons per day of reclaimed water, some of which is used for industrial and irrigation purposes, and the 80 million gallon-per-day Tillman Water Reclamation Plant, which supplies irrigation water to the Sepulveda Dam Recreation Area and will begin to supply reclaimed water for groundwater recharge in 1998.

Reclaimed water is used to maintain golf courses, as power plant cooling water, and for freeway and park landscaping. The huge Forest Lawn Memorial Park, an area tourist attraction as well as a final resting place for many residents, also relies on reclaimed water to keeps its lawns green.

In the far western portion of the watershed, the Las Virgenes Municipal Water District's Tapia Water for a Mini Greenhouse Reclamation Plant also reclaims treated wastewater from the Malibu Creek Watershed for public irrigation.


Home Page | Citizen Actions | Government Actions | Bay Play | Bay Ecosystems | Human Impacts | What's Happening? | Watershed

For more information, contact
Last Update 10/00