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<br />~ <br />C'"': <br />00 <br />-' <br /> <br />c <br /> <br /> <br />HOOl'l'1" Dam COll!rols and rcgul(l!l's rhe Colorado River for multipurpose uses. <br /> <br />The Sediment Menace Rednced <br /> <br />The Colorado is named for its reddish- <br />brown color, which comes from the <br />sediment it carries. Engineers have <br />estimated that, prior to construction of <br />Glen Canyon Dam, the. river's average <br />flow carried 266 tons of sediment and <br />sand past the Bright Angel gauging station <br />in Grand Canyon each minute, or <br />383,040 tons cvcry 24 hours. <br />Hoover Dam has trapped hundreds of <br />millions of tons of sediment in Lake <br /> <br />Mead, significantly reducing downstream <br />problems formerly caused by this silt <br />load. <br />This sediment, untrapped, not only <br />obstructed diversion works, canals, and <br />ditches, it also created a dangerous situa- <br />tion in the lower Colorado River as it <br />was deposited. A committee of the <br />United States Senate reponed in 1928: <br /> <br />we river has an annual discharge at <br />Yuma oj more than 100,(}(}() acrejeet oj <br />silt. This silt greatly aggravates the flood <br />menace. No tempOral}' works can be <br />built to hold it. It was the silt deposit <br />that built the deltaic ridge on which the <br />river now flows. It was the silt deposit <br />that filled Bee River and Volcano Lake, <br />so that the river could no longer be held <br />at that point, and the same silt deposit <br />will quickly fill the depression where the <br />river now flows. <br /> <br />33 <br />