California's Water: Facts on "California's Water System

Water Supply Overview

• Precipitation varies widely from year to year. In average years, close to 200 million acre-feet (MAF) of water falls in the form of rain or snow in California.One acre-foot is about 326,000 gallons, or enough water to supply two typical families for a year.
  
• Over half of that water soaks into the ground, evaporates or is used by native vegetation. That leaves somewhere around 82 million acre-feet of usable surface water in average years.
  
• Of that water:
  • 48% goes to environmental uses such as instream flows, wild and scenic river flows, required Delta outflow and managed wetlands.
  • 41% is used by agriculture
  • 9% is used by cities and industry.
    
• About 75% of California’s available water occurs north of Sacramento, while about 80% of the demand occurs in the southern two-thirds of the state.
  
• Most of the rain and snowfall occurs between October and April, while demand is highest during the hot and dry summer months.
  
• Groundwater provides about 40% of the state’s water supply. In dry years, that percentage can go as high as 60%.
  
• California is prone to both droughts and floods. The most recent prolonged dry spell was a six-year drought from 1987 to 1992. The most severe drought on record occurred in two consecutive years, 1976 and 1977, in which California received very little precipitation and surface water reservoirs were extremely low.
  

Water Delivery System

• California's communities, farms and businesses rely on water from a variety of sources. Surface water projects, which capture and deliver rain and snow runoff, provide a major portion of the state's total water supply. The projects include more than 1,000 federal, state and local reservoirs and hundreds of miles of canals and pipelines.
  
• Two of the most important projects are the federal Central Valley Project (CVP) and the State Water Project (SWP). The CVP and SWP bring water from Northern California through the Sacramento-San Joaquin River Delta for delivery to users in the San Joaquin Valley, parts of the San Francisco Bay Area and Southern California.
  
• Key water projects and the amount of water they deliver:
  
  • Central Valley Project (federal). Delivers about 7 million acre-feet (MAF) per year. Constructed in 1930s - 1950s.
  • State Water Project (state). Delivers about 2.3 MAF / year. Constructed in 1960s – early 1970s.
  • All-American Canal (local). Delivers 3 MAF / year. Constructed in 1930s.
  • Colorado River Aqueduct (local). Delivers 1.2 MAF / year. Completed in 1941.
  • Los Angeles Aqueduct (local). Delivers 200,000 AF / year. Completed in 1913.
  • Mokelumne Aqueduct (local). Delivers 364,000 AF / year. Completed in 1929. Second aqueduct completed in 1949.
  • San Francisco Hetch Hetchy Project (local). Delivers 330,000 AF / year. Completed in 1923.

Facts about the State Water Project

• The SWP is the nation’s largest state-built water development and conveyance system.

• Constructed and operated by the California Department of Water Resources, it provides water supplies for 23 million Californians and 755,00 acres of irrigated farmland.

• The SWP includes reservoirs and pumping plants that move water through canals, underground pipelines, siphons and tunnels.

• One of the best-known features is the 444-mile California Aqueduct, which delivers water to the San Joaquin Valley, parts of the San Francisco Bay Area and Southern California. It is visible from Interstate 5 at several points in the San Joaquin Valley.

• SWP power plants generate much of the energy used to transport the water to cities and farms around the state.

Facts about the California Aqueduct

• The 444-mile California Aqueduct is a key feature of the SWP.

• The aqueduct begins at the Harvey O. Banks Pumping Plant in the south Delta, which draws water out of the Sacramento-San Joaquin River Delta and lifts it 244 feet into the canal.

• From there, water begins its journey through the largest aqueduct system in the world, finally ending in Los Angeles.

• There are many canals, reservoirs and pumping stations along the course of the aqueduct, which travels down the western edge of the San Joaquin Valley and supplies water to the agricultural communities of the San Joaquin Valley and urban Southern California. Water is also delivered to the south San Francisco Bay Area via San Luis Division.

• In the central San Joaquin Valley near Kettleman City, the Coastal Branch of the California Aqueduct splits off from the main aqueduct. The Coastal Branch, completed in 1997, serves San Luis Obispo and Santa Barbara counties.

• The water in the mainstem aqueduct is pumped up California’s hilly terrain by three pumping plants— Buena Vista, Teerink, and Chrisman— until it reaches Edmonston Pumping Plant, the SWP’s largest. Its huge motor-pump units, each standing about 65 feet tall and weighing more than 400 tons, lift water nearly 2,000 feet up and over the Tehachapi Mountains through 10 miles of tunnels.

• As the water reaches the bottom of the mountain, it splits into two branches: the West Branch and the East Branch (the mainstem). Water in the West Branch is pumped by Oso Pumping Plant into Quail Lake. From there, it enters a pipeline leading into Warne Powerplant to generate power.

• Water is then discharged into Pyramid Lake, travels through Angeles Tunnel, and into Castaic PowerplantAt the end of the West Branch is Castaic Lake and Castaic Lagoon, a popular Southern California recreation spot.

• Water flowing down the East Branch generates power at Alamo Powerplant then is pumped uphill by Pearblossom Pumping Plant. The plant lifts the water 540 feet. From there, it flows downhill through an open aqueduct, linked at its end to four underground pipelines which carry the water into the Mojave Siphon Powerplant, which discharges the water into Lake Silverwood. When water is needed, it is discharged into Devil Canyon Powerplant and its two afterbays. The 28-mile-long Santa Ana Pipeline then takes it underground to Lake Perris, the southernmost SWP facility and one of Southern California's most popular recreation spots.

Facts About Banks Pumping Plant

• The Harvey O. Banks Delta Pumping Plant lies in the southern Delta, roughly 20 miles southwest of Stockton.

• Marking the beginning of the California Aqueduct, the plant lifts water 244 feet into the canal.

• During its construction (1963-1969), seven pumps were installed. In 1986, four more were added to diver and pump more water during wet months to fill off-stream storage reservoirs and groundwater basins south of the Delta to improve water supply reliability.

• Its pumps have the capacity to pump 10,670 cubic feet per second.

• Local water agencies perform a number of functions to deliver water to California’s communities, farms and businesses.

• Water agencies are as varied as the communities they serve. They range in size from small irrigation districts serving a few dozen farms to large urban agencies that serve millions of customers.

• Many agencies purchase water from the major state and federal water projects. They then treat the water as needed, and deliver it to their customers. Others act as wholesale agencies that buy or import water and sell it to retail water suppliers.

• Some agencies operate their own local water supply systems, including reservoirs and canals that store and move water as needed.

• Many agencies rely on groundwater exclusively, and operate local wells and distribution systems.

• In recent decades, local agencies have developed more diversified sources of water supplies. Many agencies use a combination of imported surface water and local groundwater. They also produce or purchase recycled water for use in irrigating golf courses and other landscaping.

• Many coastal agencies are pursuing ocean desalination projects to further diversify their water supplies. Other agencies operate plants that desalinate brackish groundwater.

• Some agencies have worked out water transfer agreements in which they purchase water from other agencies.

• Urban and agricultural agencies have invested hundreds of millions of dollars in water conservation and water use efficiency programs that reduce demand for water. Today, urban Southern California uses the same amount of water it used a few decades ago, even though its population has grown tremendously.

• Water agencies throughout the state are moving toward integrated regional water management planning, which generally includes a mix of programs such as water recycling, water use efficiency, groundwater management and conjunctive use, water transfers, flood protection and watershed management.

• In addition to providing water supplies, many local water agencies have responsibility for providing local flood control and flood protection. Some are responsible for managing and replenishing groundwater basins, while others also treat wastewater.

• Many local water agencies also play a role in managing watersheds, maintaining parks and other recreation facilities.