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' <br />� <br />' <br />�� <br />to have demand patterns representative of the needs in the project area as those needs are affected by <br />' local climatic conditions and water management practices.) <br />The Clay Report presented a 180,000-af reservoir to serve multiple uses including municipal and <br />' industrial (M&I) demand up to 40,800 af/yr. Contemplated uses in the Clay Report include hydropower <br />production, irrigation under the Orchard Mesa Irrigation District system (OMID), and maintenance <br />flows for endangered fish in the 15-Mile Reach. The report does not present details about reservoir <br />' demands and operations. For example, Table C-1 on the Summary Page GVL in the Clay Report does <br />not list irrigation as a use, although eliminating OMID's hydraulic pumping plant, and OMID converting <br />to pressure pipe delivery are mentioned in the discussion of "Potential Beneficiaries and <br />, Accomplishments". Table B-1, Grand Valley Lake Monthly Operation Study in the Clay Report shows <br />releases from the reservoir to OMID, as well as for power and M&I use, but no releases for fish <br />maintenance. This last use is identified in Table C-1 and described as potentially benefiting from the <br />' project. AECOM proceeded by developing a demand pattern for the larger reservoir that reflects <br />concepts presented in the Clay Report, and using reasonable assumptions and engineering judgment to <br />supply details. <br />1. Irrigation Demand <br />For the larger reservoir AECOM assumed that the four uses of the reservoir cited in the Clay <br />Report will be served by Grand Valley Lake. In particular, the lake will supply all of OMID's <br />water demand. Annual demand for OMID was set at 58,300 af/yr, based on CWCB input. The <br />CDSS model uses a monthly time series of irrigation demand for OMID that was estimated by <br />parsing the Cameo diversions at the Colorado River. These include water for the Grand Valley <br />Project, as well as supply for the USA power plant and the OMID hydraulic pump — all in <br />addition to the OMID irrigation demand. The CDSS estimate is about 10 percent higher than the <br />information from the CWCB., at least in terms of annual average. The CWCB information on <br />the demand is believed to be more accurate, so demand was set at 58,300 af/yr, and distributed <br />monthly in accordance with the CDSS time series' average monthly pattern of use. <br />As noted earlier, estimation of firm yield is an iterative process. For the larger reservoir <br />(Alignment 1), the irrigation component of demand was set to 58,300 af regardless of the annual <br />demand tested. It was assumed that the project would not be attractive to OMID unless Grand <br />Valley Lake reliably and completely served their needs. Other uses were allowed to fluctuate, <br />depending on the total annual demand. <br />The initial demand pattern for the smaller reservoir (Alignment 2), for which the size was <br />determined based on a reasonable reservoir alignment with a normal water surface elevation of <br />4990, was made up solely of the OMID irrigation demand. Before model execution, it was not <br />known whether the smaller reservoir could deliver the full OMID demand in every year, ar <br />39 <br />� AECOM 2i22i� o <br />