California's Water Delivery System

Instructor: Christopher Muscato

Chris has a master's degree in history and teaches at the University of Northern Colorado.

The people of California need water. That should be obvious, but how they get it is a bit more interesting. In this lesson, we'll talk about how California handles its diverse water needs.

Dry State, Wet State

The state of California is a place of diversity. It is home to substantial Latino, Asian, African American, and Caucasian populations, as well as others. There's one thing all of these people have in common, however: they all use water. Every single one of 'em.

This can be a challenge because while California is a large state, its climate is as diverse as its people. The northern part of the state receives abundant rainfall, but the most densely populated regions are in the arid southern desert. The central valleys, where most of the food in California is grown, rely on runoff from melted snow in the mountains.

Overall, California receives about 200 million acre-feet of precipitation per year. 65% evaporates or is consumed by plants. About 11% flows into the Pacific Ocean and mixes with salt water. The last 24% has to be shared amongst California's industries, farms, and cities and the roughly 39 million people who call this state home.

This dam on San Luis Creek creates the San Luis Reservoir in Merced County

How Does Water Move in California?

So how does water get to where people need it in California? A lot of water enters the state, but making sure that this water is available when and where people need it is not always easy. This is especially true considering that California's already diverse climate changes throughout the year. Most rainfall occurs between October and April, while summers are hot and dry. So, water needs to be stored for the dry months, distributed across the state, and treated for human and agricultural use. It's a lot to do.

In order to tackle all of this, California relies on an intricate system of water storage and delivery called the California State Water Project or SWP. The SWP is the nation's largest state-built water system, comprised of 34 major water storage facilities, 20 pumping plants, 4 pumping-generating plants, 5 hydroelectric power plants, dozens of reservoirs and lakes, and over 700 miles of canals and pipelines. This system is so complex that it requires its own agency to operate it, called the California Department of Water Resources.

The California State Water Project, as well as a federally-operated water delivery system called the Central Valley Project, are primarily responsible for bringing the billions of gallons of precipitation that mainly occur in the northern part of the state down into the central valleys and southern deserts. These two water projects combined transport around 9.3 million acre-feet per year (which is a lot of water).

The Colorado River is one major source of water for California
Colorado River

Other Aqueduct Systems in California

Apart from the Central Valley and State Water Projects, there are 5 other major aqueduct systems in California, mostly operated by cities or districts below the state level.

  • The All-American Canal in southeastern California brings water from the Colorado River to the Imperial Valley along California's Mexican border.
  • The Colorado River Aqueduct is another major water source in southern California around Los Angeles.
  • The Los Angeles Aqueduct also supplies this major city in southern California
  • The Mokelumne Aqueduct through central California supplies the East Bay and San Francisco
  • The San Francisco Hetch Hetchy Project transports water from the Yosemite region into the Bay Area.

Workers building the Los Angeles Aqueduct, 1912. Aqueduct construction was a major project throughout California history.
Pipe construction

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