WSP04003 - Laserfiche WebLink

Home Browse Search

C> an o M <= ipal and industrial water for many communities in Nevada, Arizona and California. The Metropolitan Water District of Southern California, which serves most of the area around Los Angeles, is one of the largest importers of water from the Lower Colorado River. Relatively inexpensive gydroelectric power produced by plants at Hoover, Davis and Parker darns is another lower Colo- rado River resource of great importance outside the floodplain. .,~~i Numerous darns and reservoirs have been constructed on the Colorado River and its tributaries. (For additional information on existing protective measures, see Appendix D.) Table 1 lists the more pertinent structures. In addition to the storage darns listed in Table 1, several diversion darns direct water from the lower colorado River into canal systems serving various areas in the lower basin. Headgate Rock Darn, located near Parker, Arizona, diverts water to serve Parker Valley. The Palo Verde Diversion Darn regulates flows to canals in the area of Blythe, California. Imperial Darn controls diversions into an elaborate system of canals that serves both sides of the river, in the Yuma area as well as the vast agricultural complex in the Imperial Valley of southern California. The construction of darns on the Colorado River resulted in secondary problems that have assumed great importance. Although the flow of the Colorado River has been regulated, stabilization of the river channel has not. consequently, the river had to undergo significant changes as it adjusted to its new environment. Each reservoir, acting as a sediment trap, cleared up the muddy water and released clear water, which then picked up sediment deposited by earlier floods. Waterborne sediment was t+ansported downstream and deposited on the riverbed by the slow-moving water at the head of the next reservoir. ,','-~ , (/?:~ Thus, the reaches of the river below the darns were scoured and deepened, whereas other reaches, like Topock Gorge and the reach above Imperial Darn, were raised by extensive sediment deposits. The effects of the raised riverbed in Topock Gorge extended north to the City of Needles. ' Flood History Prior to construction of Hoover Darn, high flows along the Lower Colorado River occurred seasonally. Floods occurred as a result of snow melt runoff, large rainstorms in the upper basin, and rainflows on larger tributaries. The largest flood for which a historical record exists occurred in 1884 with an estimated peak flow at Black Canyon, site of Hoover Darn, between 250,000 and 300,000 cfs. Historical and modern records indicate annual maximum peak flows at Black Canyon have probably exceeded 100,000 cfs 31 times between 1878 and 1976; during this period, flows estimated in excess of 200,000 cfs occurred 3 times. 8