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<br />FAct OF DllM e"
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<br />lhat point, and the same silt deposit will quickly fill the depression where
<br />the river now flows.
<br />"The gradient to the north into Imperial Valley is much greater than that
<br />to the south into the Gulf. and when the depression is filled there is no
<br />means known which, at any cost within reason, can prevent the river from
<br />again flowing into the Imperial Valley.
<br />"The dam proposed in this bill will catch and hold the silt. Most of the
<br />silt finding its way onto the delta is from and ahove the canyon section.
<br />If no other darns were provided on the river, the one proposed in this hi II
<br />would retain 811 of the silt finding its way into the reservoir for a period
<br />of 300 years, and for more than 100 years before its storage capacity and
<br />usefulness would be seriously interfered 'with. As other dams are coo-
<br />structed on the river they will catch and retain the silt, thereby further
<br />extending the usefulness of the Boulder Canyon Reservoir,"
<br />Reclamation engineers set aside 5,000,000 to 8,000,000 acre.feet of
<br />Hoover Dam's reservoir capacity for the job of settling out the silt. The deep
<br />reservoir forms a natural trap for the silt swept down the river. The flow
<br />.slackens as it enters the lake and the silt, heavier than the water, sinks to
<br />the bottom of the reservoir, leaving the water above clear. As the silt drops
<br />down into the deep bottom of Hoover Dam's reservoir, blue Lake Mead bears
<br />witness that the task is well performed.
<br />
<br />NEVADA WING
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<br />ARllONA WING
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<br />lONGITUOiNAlSECTrON
<br />
<br />PLAN OF POWER HOUSE
<br />SHOWING DATES OF FIRST REGULAR OPERATION
<br />
<br />The Colorado gets its name from its reddish-brown color, and the reddish-
<br />brown color comes from the silt carried in its turbulent waters. Engineers
<br />have estimated that the average flow of the river carries 330 tons of silt and
<br />sand past a given point every single minute of the day and night.
<br />This silt not only obstructs the diversion works, canals, and ditches of
<br />those who wish to use the water, hut its deposition is dangerous. Silt de-
<br />posits result in the gradual building up of the ground elevation. A
<br />committee of the United States Senate in 1923 reported as follows:
<br />"The river has an annual discharge at Yuma of more than 100,000 acre-
<br />feet of silt. This silt greatly aggravates the flood menace. No temporary
<br />works can be built to hold it. It was the silt deposit that built the deltaic
<br />ridge on which the river now flows. It was the silt deposit that filled the
<br />Bee River and V oleano Lake, so that the river could no longer be held at
<br />
<br />Tunnel
<br />..PIiK)
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<br />Arizona Spillway Tunnel
<br />SO' DIameter
<br />2pOO. in len9th
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<br />T;',s dro"'",,? dlvstrales .Ihe mC'''''li'r in w;,ichhoov/ff Dam "'ods. The """""de wall of Black Canyon IS shown as Solil1.
<br />,,,,;,,,reas IIle Arl:MO ,.,,011 ,s cvt Ow'!}' to re,..ed f~ mtake lo,"""T;';, Ik sp,/I",ay. IIui p<!l>.'itock P'i;:u: ond outlet works.
<br />In.,,!,, thB N..VQda woJI or Ill.. =nyan 0 Slm'/ar SR' 01' d,~"rSIl:m works has bHn placed Porn;,pol alme,,=,,< 0,.. show"
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