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Managing water scarcity in California

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Managing water scarcity in California, one of the driest states in the USA

California is one of the driest states in the United States with an average annual precipitation of 22.2 inches (563mm). The rainy season spread from October through April. It rarely rains from May until September. However, northern California, including the Sierra Mountains, received on average 51.8 inches (1316 mm) of precipitation, including precipitation and snowfall. This average comes from eight major precipitation sites as shown in the figure.

Figure 1. Northern California weather stations (source cdec.water.ca.gov)

Challengers faces

The precipitation in California is highly variable from year to year and is limited to a maximum of six months in a typical year. Over the past three years, average rainfall in Northern California has been lower than average (Figure 2). Water managers face the challenge of distributing the limited precipitation received in whole year along to supply urban, agricultural, industrial water demands, power generation, recreation use, and manage the Sacramento – San Joaquin Delta salinity.

The demand is managed by storing the precipitation in a series of reservoirs and release with the demand and water rights. Some rainy years. The mountains of northern California and the Sierra receive excessive amounts of rainfall which cause flooding. Northern California represents 70 percent of total precipitation in the state. The reservoirs regulate flooding and therefore never allow it to be filled to full capacity during the winter months to hold back emergency flood waters.

Computer models are used to give guidance to manage the water supply and efficiently manage the reservoirs. Along with many other reservoirs California used three main reservoirs (Oroville, Shasta, and Folsom) to manage the water demand. These reservoirs are managed by California State and Federal governments.  In the dry years where the reservoir water cannot meet the demand, urban, agricultural, and industrial water supply depends on groundwater.

Figure 2. Northern California average rainfall. (Source: cdec.water.ca.gov)

How to face the California water shortage challenges

With a series of reservoirs and the world’s largest man-made water distribution system manage with state-of-the-art computer models used to efficiently distribute the limited water resources to state consumers. Brief description of major reservoirs is as follows.

Major reservoirs

Lake Oroville: 

Located on California’s Feather River, the Oroville Dam is the tallest dam in the United States at 770 feet. At its base, it extends for three-quarters of a mile. This dam is designed to control the Lake Oroville reservoir, with about 3.5 million acre-feet capacity, which provides drinking water, hydroelectric power, and water-based recreation while minimizing flood damage. Officially dedicated in 1968 after seven years of construction, the dam has stood for fifty years.

Lake Shasta:

With a total capacity of 4.5 million acre-feet, an elevation of 1,067 feet, 365 miles of mostly mountainous shoreline, and a maximum depth of 517 feet, Lake Shasta are California’s largest reservoir and the eighth largest in the United States. Lake Shasta is impounded by the Shasta Dam (Figure 3), a concrete arch gravity dam across the Sacramento River that stands 602 feet tall, making it the eighth tallest dam in the United States. Operated by the Bureau of Reclamation, the reservoir provides water storage, flood control, hydroelectricity, and protection against the intrusion of salt water.

The Shasta Power Plant contains five huge generators capable of producing 710 megawatts, and recent upgrades have increased their efficiency rating to 98%. Originally built to control the waters of the Sacramento, the McCloud, and the Pit Rivers, the reservoir has since become one of the most popular vacation spots in the western United States. Providing thousands of jobs for people still suffering from the Great Depression, construction of the dam began in 1935 and was completed in 1945.

Lake Folsom:

Folsom Lake was created in 1955 by Folsom Dam, a concrete dam flanked by earth wing dams and dikes with a total length of about 9 miles. The lake features some 10,000 surface acres of water when full and has 75 miles of shoreline and capacity is about one million acre-feet. The Lake level normally varies about 40 feet from early summer to early winter.

To be continued …

Figure 3: Shasta Dam

Nimal C. Jayasundara
Nimal C. Jayasundara
Ph.D., PE. Water Resources Engineer, California Department of Water Resources, California.


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