WSP13016

• File Number: 8282.600.10.B
• Description: 2000 Annual Operating Plan
• Basin: Colorado Mainstem
• Author: USDOI/BOR
• Title: 29th Annual Report and 2000 Annual Operating Plan for Colorado Riber System Reservoirs
• Water Supply Pro - Doc Type: Publication

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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 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 Morelos Dam.

The Yuma Area Office 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, local governments, and other State
and Federal agencies.

The overall project has been developed in phases. Phase 1 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 1 consisted of limited 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.

Phase 2 of the project is scheduled to begin in September 1999. Phase 2 consists 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 control releases experienced during the winters of 1997 and 1998,
as well as the natural dynamic nature of the river system, make this review prudent.

Limitrophe Division Below Morelos Dam

The International Boundary and Water Commission (IBWC) has initiated the development of
an Environmental Impact Statement (BIS) 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 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 Valley. The BIS will identify the best U.S.lMexican alternative to
be undertaken for the proposed project.

December 1, 1999

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