Retrogression on the Lower Colorado River After 1935

River surveys on the Colorado River below Hoover Dam in Arizona Nevada and Arizona-California indicate that approximately 125,000,000 cu yd of material was scoured from the river bed between the dam and Havasu Lake from 1935 to 1946. Steepening of the river slope for many miles downstream has resulted. From the time of the Parker Dam closure in 1938 to 1946 approximately 135,000,000 cu yd was removed downstream from Parker Dam. The major part of this material was deposited in the Imperial Reservoir area until 1945, since which time nearly all the sediment has been carried past Imperial Dam. River surveys begun below Imperial Dam in 1940 indicate that approximately 65,000,000 cu yd of material was removed from the river bed between Imperial Dam and the International Boundary from 1940 to 1946. The suspended sediment lo ad carried by the Colorado River at Yuma has been reduced to approximately 10,000 tons per day at a discharge of 10,000 eu ft per sec from the approximately 100,000 tons per day which it carried at the same discharge before Hoover Dam was closed.