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I I I I a I I I I I I I I I I I I I I OD25~7 Imperial Dam. This division receives the sediment generated in the Parker, Palo Verde, and Cibola Divisions. The sediment load arriving in the Imperial Division is either deposited in the overflow areas outside of the main channel or eventually arrives at Imperial Dam to be removed in the desilting works and the forebay of the dam. In planning for the Parker, Palo Verde, and Cibola Divisions, reducing the sediment flowing into the Imperial Division was a major objective. Reclamation continually collects and processes data on sediment transported by the river. This allows needs to be defined, appropriate corrective measures to be instituted, and the results of control measures to be adequately evaluated. Most of the diverted sediment is removed by the Desilting Works for the All-American Canal, returned to the river below Imperial Dam and dredged to permanent dry land storage areas near the Laguna Settling Basin, located about 1 mile above Laguna Dam. The desilting works for the Gila Gravity Canal are maintained periodically, by sluicing sediment accumulations down to the Laguna Settling Basin for removal by dredging. Dredging above Imperial Dam is conducted periodically to maintain diversions for water demand into the All-American Canal on the west end of the dam and the Gila Gravity Main Canal on the east end. In the main channel above the California sluice gates on the California side of Imperial Dam, about 900,000 cubic yards of material have accumulated over a period of years. This material will eventually be pumped into the river channel below the dam, probably in the next 3 to 5 years. This area is approximately 480 feet by 2,500 feet and is to be cleaned to a depth of about 20 feet. Normally it takes approximately 6 months to a year to clean this area. The Gila Gravity con~eyance channel, just upstream from the dam face, has required periodic work. About 300,000 cubic yards of sediment accumulated here over a period of years and eventually must be pumped by dredge into the river channel below the dam gate for transportation to the Laguna Basin; probably some time in the next 2 to 3 years. This channel is approximately 360 feet wide by 1500 feet long and is dug to an average depth of 15 feet for a total of 300,000 cubic yards of sediment. Working a two-shift schedule it would take 4 months to clean the channel. Laguna Division The Laguna Division includes the area between Imperial and Laguna Dams. The Laguna Division receives the ~ediment returned from the All-American Canal Desilting Works. Because this created problems associated with Mexican diversions at Morelos Dam, in the mid 196Os, Reclamation constructed a settling basin in the Laguna Division where sediment from upstream sources is trapped and pumped with a dredge for disposal onto dry land. Appendix C - 8