Water Education Foundation

The Colorado River

Posted by: Aquafornia on August 19, 2008 at 4:03 pm

The Colorado River is the principal water resource for California and six other states, Indian tribes and parts of Mexico. Spanning 1,440 miles from Wyoming to the Gulf of California, the Colorado River is the most regulated river in the entire world. Water in the river is governed by a complex set of interstate compacts, international treaties, Supreme Court decrees, federal laws, state laws, water contracts, and administrative decisions which together have become known as “The Law of the River”.

The Law of the River includes the 1922 Colorado River Compact, which apportions water use among the seven states, and outlines a priority system for use of the water. A 1944 U.S.-Mexico treaty allocated 1.5 MAF annually to Mexico. California’s basic apportionment from the Colorado River is 4.4 million acre-feet, plus surplus water if available. The U.S. Secretary of the Interior is the designated “water master” for the Lower Colorado River, and has authority to declare when surplus or shortage conditions exist.

California’s annual use of Colorado River water has varied between 4.5 to 5.2 million acre-feet over the last ten years. The additional water over California’s basic allocation has come from surplus conditions and unused apportionments of water by Arizona. However, these surplus conditions aren’t likely to continue much farther into the future, with persistent drought conditions occurring the Colorado River basin and with Arizona approaching full use of its apportionment.

Of California’s 4.4 million acre-feet apportionment from the Colorado River, 3.8 million acre-feet or 86% of that water goes mostly to the Imperial Valley and, to a much lesser extent, the Palo Verde Irrigation District near Blythe, the Yuma Project, and the Coachella Valley Irrigation District. The water rights held by these irrigation districts predate the 1922 Colorado River Compact. These “present perfected” water rights entitle them to receive their water allocation in all years – dry or wet – over other lower priority users, including Metropolitan Water District. Metropolitan holds a fourth priority right to 550,000 million acre-feet of water, and a fifth priority right to another 662,000 MAF.

In 2003, the largest ever agricultural to urban water transfer deal, called the QSA, was signed by the Imperial Irrigation District, San Diego County Water Authority & Metropolitan Water District. The agreement basically calls for Imperial Valley farmers to make efficiency and conservation improvements, with the conserved water then transferred to San Diego. In consideration for this, SDCWA will pay for conservation and efficiency improvements, plus provide mitigation funds to help with the economic losses. As part of the agreement, the state has agreed to bear responsibility for the restoration of the Salton Sea.

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The Salton Sea was formed in 1905 when seasonal flooding of the then untamed Colorado River burst through a poorly-constructed headgate, and sent the entire flow of the Colorado River into the Salton basin. The flooding continued for two years, inundating farms and cities, and at one point, it was feared that the floodwaters would flow as far north as Palm Springs. After at least six failed attempts to stop the flooding, the breach was finally plugged in early 1907 by a massive multi-million dollar effort led by the Southern Pacific Railroad.

Afterwards, the Salton Sea was expected to dry up, but in the years after the breach was fixed, agriculture in the Imperial Valley was expanded. The newly-carved waterways from the flood made convenient drainage channels for the fields, and the sea became sustained by these agricultural flows. In the 1920s, the Salton Sea was officially designated an agricultural sump by the President.

The agricultural runoff that sustains the sea contains salts, pesticides and fertilizers, adding about 4 million tons of salt per year to the sea. With no natural outlet, the water evaporates, leaving the salts behind, which increases the salinity. Currently, the sea is about 25% saltier than the ocean and is only getting saltier.

With over 90% of California wetlands gone, the Salton Sea is one of the few remaining wetland areas left. On any given day, 3.5 million birds use the Salton Sea and surrounding area, making it one of the nation's premier bird watching areas. The Sony Bono Salton Sea National Wildlife Refuge preserves over 35,000 acres of salt water marsh, plus 2,000 acres of freshwater marsh, with the most birds visiting in December and January. “The Salton Sea serves millions of birds, not because it is the best habitat, but because it is the only one left\”, said Thomas Kirk, former director of the Salton Sea Authority.

In 2003, the QSA agreement was signed, whereby irrigators would be paid to use their water more efficiently, with the conserved water to be transferred to San Diego. This efficiency will come at the expense of the sea, depriving it of its main flows, which are expected to decrease by more than 40% in the next 20 to 30 years.

As the Salton Sea dries up, the lake will become saltier, thus no longer being a suitable habitat for birds or fish. Winds blowing across the exposed lake beds will carry fine dust containing heavy metals, salts, and other chemicals, harming crops and further degrading air quality in a region where already state and federal air quality standards are regularly violated.

As part of the QSA agreement, the State of California agreed to be liable to restore or at least clean up the Salton Sea. The current restoration plan would take 75 years to accomplish and cost $9 billion to implement, causing many legislators balk at the price tag. Whether this restoration plan will acquire the funding needed for implementation remains to be seen.

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Water is delivered from the Colorado River to the Imperial Valley and Southern California by two different systems. The Imperial Irrigation District delivers water from the Imperial Dam through the All-American Canal to the Imperial Valley. Metropolitan Water District of Southern California owns and operates the Colorado River Aqueduct, delivering water from Parker Dam to Riverside for distribution to the southern portion of its service area, which includes the Inland Empire and San Diego.


With over 3,000 miles of canals and drains, and delivering 3.1 million acre-feet to 500,000 acres of prime farmland, the Imperial Irrigation District is the largest irrigation district in the nation. It was formed in 1911 to acquire the bankrupt California Development Corporation's property and facilities to import and distribute Colorado River water to the Imperial Valley. IID holds legal title to all its water and water rights which it holds in trust for landowners and water users.

With the purchase of the CDC, the IID also acquired the long-standing right to divert 3.1 million acre-feet from the Colorado River, an amount more than any other state or entity on the Colorado River. These rights date back as early as 1885, and are considered senior to Metropolitan Water District's entitlement.

The Imperial Valley's fertile soils and warm climate have made it one the world's most productive agricultural regions, with fields capable of producing multiple harvests per year. The Imperial Valley is the tenth largest agricultural county in the nation, producing $1.2 billion in vegetables, melons, fruits, nuts, field crops, livestock production, and more.

The Colorado River contains a high amount of salt when it enters the IID system; this saltiness combined with the clay underlying the Imperial Valley results in an accumulation of salts in the root zone of the plants. This can result in smaller plants and lower crop yields. A subsurface drainage system consisting of perforated pipes installed underneath the fields is used to drain the salts. To date, 95% of the Imperial Valley’s fields have subsurface drains installed. IID maintains a 1,400 mile network of open drainage ditches which carry the salty irrigation water to the Salton Sea.

Leaching the soil of excess salts in arid and semi-arid regions is an essential and necessary agricultural practice. While water conservation practices can improve water use efficiency, this drainage water cannot be eliminated.

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Shortly after completion of the Los Angeles Aqueduct, booming population growth and drought sent Mulholland and the City looking for additional water sources. In 1928, the Metropolitan Water District of Southern California was organized as a public corporation, pursuant to special legislation enacted by the state legislature. This legislation provided a way for cities and smaller governmental entities to join together to develop a regional water supply. The 13 original members of the MWD are Anaheim, Beverly Hills, Burbank, Compton, Fullerton, Glendale, Long Beach, Los Angeles, Pasadena, San Marino, Santa Ana, Santa Monica, and Torrance. MWD has since added another thirteen members.

Today the Metropolitan Water District is by far the largest water agency in California, if not the entire United States. MWD serves 18 million customers over 5200 square miles, a service area extending from Ventura County down to San Diego.

The Metropolitan Water District manages the 242-mile long Colorado River Aqueduct, which extends from Parker Dam at Lake Havasu, Arizona, to Lake Matthews, near Riverside. The Colorado River Aqueduct’s capacity is 1.3 million acre-feet annually. The water travels through 63 miles of canals, 92 miles of tunnels, 55 miles of conduit, and 144 underground siphons. Metropolitan’s water system includes 5 pumping plants, 9 water treatment plants, and 9 reservoirs, with a total capacity of 1,972,000 acre-feet of water storage.

California has previously relied on surplus conditions and the unused apportionments of Arizona and the other states.   However, while California’s apportionment of water has priority over Arizona and Nevada, increasing use of the Colorado River by Arizona and other states along with diminished supplies due to persistent drought conditions and climate change could eventually reduce the amount of water available to Metropolitan to only its fourth priority right of 550,000 million acre-feet, plus what water could be made available from conservation programs with the Imperial Irrigation District and other agricultural-to-urban water transfers.

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