WSP05551

• File Number: 822.600.10
• Description: Colorado River Annual Operating Plan - Annual Reports
• Basin: Colorado Mainstem
• Date: 1/1/2002
• Author: USDOI/BOR
• Title: Annual Operating Plan
• Water Supply Pro - Doc Type: Annual Report

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classes to the public in water treatment by reverse osmosis. The first class started in August 1999
in cooperation with Arizona Western College in Yuma and graduated in the spring of2001.

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Colorado Ri\-'er Channel Aggradation Below Gila River Confluence

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The 1993 Gila River flood deposited approximately 10 million cubic yards of sediment in the
Colorado River between its confluence with the Gila and Moreles Dam. An additional
unspecified volume of sediment was deposited in the river chaTU1e1 below Morelos Dam, The
aggradation of the channel has substantially reduced the river's capability to carry flood flows,
to act as a drain for groundwater, and has occasionally caused operational problems with the
delivery of Treaty water to Mexico at Morelas Dam.

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The Yuma Area Office developed a project proposal to address the aggradation problems in
cooperation with local irrigation districts, the IBWC, Native American Tribes. local
environmental organizations. local governments, and other state and federal agencies.

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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 of1997 and 1998. Phase 1 consisted oflimited clearing ofa flow path
in the channel below Morelos 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.

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Phase 2 of the project began in September 1999, Phase 2 consisted of dredging a sediment basin
in the river channel immediately upstream of r>.10relos 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 l\1exico at Morelos Dam. Phase 2 was completed in April of
2001.

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The need for completing Phases 3 and 4 of the project is currently being reviewed and studied.
The space building and flood control releases experienced during the winters of 1997, 1998, and
1999, as well as the natural dynamic nature of the river system, make this review prudent.

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Limitrophe Division Below Mor-elos Dam

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The 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 Limitrophe section of the Colorado River. The flood events of 1983 and 1993 have
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 groundwater levels in the Yuma Valley. The EIS will
identify the best U.S.lMexico alternative to be undertaken for the proposed project.

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October 15, 2001

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