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I I I I I I I I I I I I I I I I I I I Colorado River Channel Aggradation below Gila River Confluence The 1993 Gila River flood deposited approximately 10 million cubic yards of sediment in the Colorado River between its confluence with the Gila and Morelos Dam. An additional unspecified volume of sediment was deposited in the river channel below Morelos Dam. The aggradation of the ehannel has substantially reduced the river's eapability to carry flood flows, to act as a drain for groundwater, and has oecasionally eaused operational problems with the delivery of Treaty water to Mexico at Morelos Dam. The Yuma Area Offiee developed a project proposal to solve the aggradation problems, in cooperation with local irrigation districts, the International Boundary and Water Commission, Native American Tribes, local environmental organizations, loeal governments, and other State and Federal agencies. The overall project has been developed in phases. Phase I of the project was completed in late 1997 so the channel below Morelos Dam could accommodate flood control releases from Hoover Dam during the winters of 1997 and 1998. Phase I consisted of limited clearing of a flow path in the channel below More\os Dam, and realignment of the channel upstream of Yuma at River Mile 31, where the levee was in danger of being breached during high flows. Phase 2 of the project is scheduled to begin in September 1999. Phase 2 eonsists of dredging a sediment basin in the river channel immediately upstream of Morel os Dam to a location about one mile above the NIB. The sediment basin will alleviate most of the operational problems due to sediment laden waters being delivered to Mexico at Morelos Dam. Dredging of this basin is scheduled to last until September 2000. The need for completing Phases 3 and 4 of the project is currently being reviewed and studied, The space-building and flood eontrol releases experienced during the winters of I 997 and 1998, as well as the natural dynamie nature of the river system, make this review prudent. Limitropbe Division Below Morelos Dam The International Boundary and Water Commission (IBWC) has initiated the development of an Environmental Impact Statement (EIS) to address the work necessary to develop and undertake a boundary preservation project within the Iimitrophe section of the Colorado River. The flood events of 1983 and 1993 has changed the course of the river and deposited approximately 10 million cubic yards of material within the first 5.5 miles of the river below Morelos Dam affecting the carrying capacity of the river and contributing to higher ground water levels in the Yuma ValJey. The EIS will identify the best U.S.lMexican alternative to be undertaken for the proposed project. December I, 1999 15