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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />jf; <br /> <br />.';c <br /> <br />i <br />",,,' <br />~':" <br /> <br />11 <br /> <br />~.. <br /> <br />B. Environmental Change <br /> <br /> <br />Alterations in physico-chemical and biological features of the lower Colorado <br /> <br /> <br />River began in the late 1800's. The first changes involved diversion for irrigation, <br /> <br /> <br />channel manipulation, stripping of floodplain vegetation for agriculture, cutting of <br /> <br />riparian gallery forests for steamboat fuel, and early introductions of nonnative fishes. <br /> <br /> <br />Except for the last, it seems unlikely that these early actions had other than local impacts, <br /> <br /> <br />although they represented the beginning of a wave of change that has expanded over the <br /> <br />next 100 years. <br /> <br /> <br />Diversions and water-control structures of earth and wood were washed away by <br /> <br />floods, even in the early 1900's after they were replaced by more permanent installations. <br /> <br /> <br />Channelization through armoring of banks with rock (rip-rap) to control meanders and <br /> <br /> <br />other channel degradation also promoted incision, lowering local groundwaters that <br /> <br /> <br />hampered agriculture on water-logged terraces. Constraining the channel reduced the <br /> <br /> <br />amount of quiet-water habitats along shorelines and local lowering of water tables <br /> <br /> <br />drained oxbows and other floodplain depressions. Further, clearing of vegetation <br /> <br /> <br />increased vulnerability of banks and floodplains alike to erosion. <br /> <br /> <br />Catastrophic floods in 1904-07 broke through diversions and bypassed canals to <br /> <br /> <br />flow into the Salton Sink, California. Vast areas of agricultural and non-agricultural land <br /> <br /> <br />were eroded, inundated, or otherwise damaged, causing significant economic losses <br /> <br />(Sykes 1937; Di111944). Because a 12 month growing season and the invention of <br /> <br /> <br />refrigerated rail cars allowed fresh vegetables to be shipped to markets in eastern USA, <br /> <br /> <br />the region had increasing economic importance. "Taming" the Colorado River became a <br /> <br />.:.. <br />