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<br />~ <br />C\1 <br />~ <br />~'k>> <br />~:.;,/) <br />c."- <br /> <br />8. The spring snowmelt flood of 1884 was the largest histori- <br />cal flood known to have occurred in the Colorado River Basin. Accu- <br />rate determination of discharge for this flood is difficult because <br />records from the Yuma gaging station, which is the only station for <br />which records applicable to inflow estimates at Lake Mead are avail- <br />able, are complicated by lack of information on the amount of scour <br />and fill that occurred. However, estimates place the April..Jul,y <br />inflow volume at 30,200,000 acre-feet and the maXimum mean daily <br />discharge at 300,000 cubic feet per second. <br /> <br />9. The spring snowmelt flood of 1917 was the largest flood of <br />record. The April-July inflow volume for this flood was 16,900,000 <br />acre-feet, and the max1.mum mean daily discharge was 160,000 cubic <br />feet per second. . <br /> <br />10. Flood damages. --Prior to the construction of Hoover Dam, <br />disastrOllS snowmelt floods caused damage in the lower Colorado River <br />Basin each year. In addition to these floods, destructive summer <br />rainfall floods otten occurred. Levees had to be built and continu- <br />s1.l,y repaired to protect lowlands from flooding. In 1905, the river <br />broke through levees about 4 miles below the MeXican border and <br />flooded lowlanda for 16 months. The Imperial Valley was inundated, <br />railroad tracks and highways were washed away, and homes and farma <br />were destroyed. The Salton Sea; with an area of 490 square miles, <br />was formed. Dalllllges amounted to millions of dollars. From 1906 to <br />1924, a total of 10-1/4 million dollars was spent on levee work in <br />the lover Colorado River. In 1909, the Colorado River again broke <br />through levees and changed its course, causing extensive damage. <br /> <br />11. When Hoover Dam was completed in 1935, control of most <br />floods on the Colorado River to an outflow of 40,000 cubic feet per <br />second became possible. If s flood equal in magnitude to the 1884 <br />flood should again occur, it could be regulated so as to reduce the <br />peak inflow of about 3ClO,000 cubic feet per second to a peak outflow <br />of 77,000 cubic feet per second. Inflow records show that the <br />floods of 1941, 1952, and 1957 were the largest floods that have <br />occurred since construction of Hoover Dam. It was necessary to make <br />flood-control releases during the 1941 and 1952 floods. In 1941 a <br />maXimum mean daily inflow of 119,200 cubic feet per second was re- <br />duced to a max1.mum mean daily outflow of 35,500 cubic feet per <br />second. In 1952, the maXimum mean daily inflow of 122,000 cubic <br />feet per second was reduced to a maXimum mean daily outflow of 30,900 <br />cubic feet per second. In 1957 a maXimum mean daily inflow of . <br />124,000 cubic feet per second vas reduced to a maXimum mean daily <br />outflow of 18,400 cubic feet per second. Each of these three floods <br />would have caused damage estimated at many millions of dollars to <br />private property, public utilities, and flood-control structures had <br />Hoover Dam not been constructed. See succeeding paragraph titled, <br />"ChanDlll reaches with restricted capacities", for further 1nfo~tion <br />on damages which would occur under present day conditions. <br /> <br />3 <br />