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The Colorado River Basin Region covers approximately 19,900 square miles in the southeastern corner of California, the most arid area of the state. It includes all of Imperial County and portions of San Bernardino, Riverside, and San Diego Counties.
It is bounded on the east by the Colorado River; to the south by the Republic of Mexico; the west by the Laguna, San Jacinto, and San Bernardino Mountains; and to the north by the New York, Providence, Granite, Old Dad, Bristol, Rodman, and Ord Mountain Ranges.
A significant geographical feature of the Region is the Salton Trough, which contains the Salton Sea and the Coachella and Imperial Valleys. The Salton Trough is a landward extension of the Gulf of California structural depression. In prehistoric times, it contained the Ancient Lake Cahuilla (not to be confused with the present Lake Cahuilla, located at the terminus of the Coachella Branch of the All-American Canal). Much of the agricultural economy and industry of the Region is located in the Salton Trough. The Salton Trough contains the Salton Sea Known Geothermal Resource Area, which as of 2017, consisted of 10 generating geothermal plants.
The Region has the driest climate in California. The winters are mild and summers are hot. Temperatures range from below freezing to over 120oF. In the Colorado River valleys and the Salton Trough frost is a rare occurrence, and crops are grown all year round.
Snow falls in the Region's higher elevations, with mean seasonal precipitation in the upper San Jacinto and San Bernardino Mountains ranging from 30 to 40 inches. The lower elevations receive relatively little rainfall. An average of about four inches of precipitation occurs along the Colorado River, with much of this coming from late summer thunderstorms moving north from Mexico.
Typical mean seasonal precipitation in the desert valleys is 3.6 inches at Indio and 3.2 inches at El Centro. Precipitation over the entire area occurs mostly from November through April, and August through September, but its distribution and intensity are often sporadic. Local thunderstorms may contribute all the average seasonal precipitation at one time or only a trace of precipitation may be recorded at any locale for the entire season.
The Region provides habitat for a variety of native and introduced species of wildlife. Increasing human population and its associated development have adversely affected the habitat for some species, while enhancing it for others.
Large areas within the Region are inhabited by animals tolerant of arid conditions, including small rodents, coyotes, foxes, birds, and a variety of reptiles. Along the Colorado River and in the higher elevations of the San Bernardino and San Jacinto Mountains, where water is more abundant, deer, bighorn sheep, and a diversity of small animals exist.
The Region provides habitat for certain wildlife species listed as endangered or threatened under the California Endangered Species Act (CESA) and/or the federal Endangered Species Act. These species include, but are not limited to, desert pupfish, razorback sucker, Yuma clapper rail, black rail, least Bell's vireo, yellow-billed cuckoo, desert tortoise, and peninsular bighorn sheep.
The region is divided into three watersheds: the Lower Colorado River, Salton Sea Transboundary and Desert Aquifers. The Desert Aquifers Watershed has little surface water and hundreds of aquifers. The majority of the region’s surface waters are in the Imperial Valley and East Colorado River
The Colorado River Basin Region is in the most arid area of California. Despite the relatively dry climate, the Region contains some substantial surface water bodies, including the Colorado River and the Salton Sea. Many of the alluvial valleys in the Region are underlain by ground water aquifers that in many cases are the sole source of water for local areas. The most Regionally important ground water basin underlies the Coachella Valley.
The Colorado River is the most important waterway in the Region. The River supplies water for use within the Region and elsewhere. Regional drainage to the River is from a strip about 200 miles long, with a watershed which (in California) ranges from 7 to 40 miles in width. This watershed strip is referred to as the East Colorado River Basin.
Developments along California's 230-mile reach of the Colorado River, which flows along the eastern boundary of the Region, include agricultural areas in Palo Verde Valley and Bard Valley, urban centers at Needles, Blythe, and Winterhaven, several transcontinental gas compressor stations, and numerous small recreational communities. Some mining operations are located in the surrounding mountains.
The Salton Sea Transboundary Watershed, encompassing the Coachella and Imperial Valleys, is the priority watershed for the Colorado River Basin, containing five of six 303 (d)-listed impaired surface water bodies in the region. Water from the Colorado River has created an irrigated agricultural ecosystem throughout this watershed. Wildlife and aquatic species are dependent on habitat created and maintained through the discharge of agricultural return flows. Major water bodies in the watershed include the Salton Sea, Alamo River, New River, Imperial Valley Agricultural Drains, and Coachella Valley Storm Channel. The beneficial uses for this region include domestic, municipal, agricultural and industrial supply; power generation; recreation; aquaculture; wildlife habitat and preservation of aquatic life.
Historical beneficial uses of water within the Colorado River Basin Region have largely been associated with irrigated agriculture and mining. With the discovery of gold in the East Colorado River Basin about 1860, mining activities began at Picacho, California. Crops were also grown along the Colorado River to graze livestock.
In 1877, the first request was filed for use of the Colorado River water in Palo Verde Valley, California, for agricultural, mining, manufacturing, domestic, and commercial purposes.
In 1901, water was first delivered to Imperial Valley through the Canal del Alamo and was used to irrigate land. With the completion of Hoover Dam in 1935 and the All-American Canal in 1940, most of the land in the Imperial Valley was developed for agriculture. In 1949, the Coachella branch of the All-American Canal was completed which delivers water for irrigation and other beneficial uses in Coachella Valley. Today approximately 500,000 acres in Imperial Valley and about 70,000 acres in Coachella Valley are under cultivation.
Availability of good quality ground water has been very important in the development of many areas including Coachella Valley, Borrego Springs, Morongo Valley, Twentynine Palms, Joshua Tree, Yucca Valley, Lucerne Valley, and Desert Center. Industrial use of water has become increasingly important in the Region, particularly in the agricultural areas. Recreational use (both contact and non-contact uses) of the Colorado River and Salton Sea is a very important use of these waters; and this use supports millions of dollars’ worth of recreational oriented businesses.
From a quantity standpoint, agricultural use is the predominant beneficial use of water in the Colorado River Basin Region, with the major irrigated acreage being located in the Coachella, Imperial, and Palo Verde Valleys. The use of water for municipal and industrial purposes, which is second in quantity of usage, is also located largely in these valleys and in the Joshua Tree and Dale Hydrologic Units of the Lucerne Valley Planning Area. The third major category of beneficial use, recreational use of surface waters, represents another important segment of the Region's economy.
Impacts from land uses to California's water resources continue. Unless these uses are managed in a way which will minimize NPS impacts, the resource values will diminish, lowering land values and discouraging future use. The challenge of nonpoint source pollution management is to implement economically achievable protections which will preserve the resources upon which California's quality of life and economic vitality depend.
Some of the primary challenges facing the Region include pollution from Mexico, increasing salinity, selenium, and eutrophication in the Salton Sea, silt, nutrient, and pesticide pollution of the agricultural drains in Imperial Valley and the New and Alamo Rivers, and underground leaking tanks. Although legacy pesticides are no longer used commercially, traces of these contaminants can linger in the environment for decades as they bio accumulate in the bodily tissues of fish and wildlife, and these pesticides are still being detected in the Region.
Colorado River Basin Regional Water Quality Control Board’s Website
www.waterboards.ca.gov/coloradoriver/
www.waterboards.ca.gov/coloradoriver/about_us/contact_us.html
www.waterboards.ca.gov/coloradoriver/about_us/units.html
Colorado River Basin Regional Water Quality Control Board Basin Plan
www.waterboards.ca.gov/coloradoriver/water_issues/programs/basin_planning/
Colorado River Basin Regional Water Quality Control Board Factsheet
www.waterboards.ca.gov/water_issues/programs/swamp/docs/regional/r7_factsheet_18.pdf
Colorado River Basin Regional Water Quality Control Board SWAMP Factsheet
www.waterboards.ca.gov/water_issues/programs/swamp/docs/regional/r7_factsheet_18.pdf
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