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<br />002980 <br /> <br />Colorado River Decision Support System (CROSS) and is a monthly water allocation and <br />accounting model with flexibility to become a daily model. It can be used to make comparative <br />analyses for assessing various water management policies and practices utilized in the <br />administration of a river basin. The model's operation is governed by basin hydrology, water <br />rights associated with diversion and storage structures, and the operating rules used for the <br />diversion and storage structures. StateMod uses four types of water rights: direct flow rights, <br />instream flow rights, reservoir storage rights, and operational rights. Water rights are sorted by <br />priority and river administration is simulated using the Prior Appropriation Doctrine. <br /> <br />StateMod ,was selected for this analysis for several reasons. It can be operated on a monthly time <br />step that allows for fast execution and a reasonable volume of output to be analyzed. The <br />simulations on a montWy time step will generally be adequate for assessing the impacts of <br />potential changes to water management policies within the basin. In those cases where the <br />impacts need to be examined at shorter time intervals, StateMod can be set up to run on a daily <br />time step. Input to the daily version of the model can be daily data for stream flow, diversion <br />demands, and reservoir targets, or a set of values for distributing the monthly data. Daily data <br />are available on the State's database and will be used in the daily runs of StateMod as discussed <br />below in the Baseline Hydrology section. <br /> <br />Routing of reservoir releases (lag times, etc,) is not included in either the monthly or daily model <br />because: (1) StateMod is primarily a planning model; (2) the additional detail required to <br />properly implement reservoir releases with a travel time component is not justified because the <br />system would have to include some kind of forecasting to know a reservoir release is required <br />before a reservoir demand occurs; and (3) the volume of water associated with a potential <br />under-release that occurs by ignoring travel time before a reservoir demand is known is offset by <br />the potential over-release that occurs after the demand is satisfied. <br /> <br />I' <br /> <br />h <br /> <br />2.3.2 Baseline Hydrology <br /> <br />ThePBO employs the hydrology from the Cl Scenario developed for the PBO for investigative <br />purposes. In the CI Scenario irrigation demands are calculated from average irrigation <br />efficiencies for the study period, 1975-1991. Irrigation efficiencies were calculated for CROSS <br />based on historic data for the Colorado River Basin in Colorado (Moore, 1999). The <br />C 1 Scenario also includes "backcasting" of 1995 water year demands throughout the entire study <br />period for selected major structures. Average annual depletions for these existing demands are <br />used for every year. Depletions from demands that were in place for only a portion of the <br />1975-19911975 period were included in the Cl run for the entire study period. Depletions from <br />new demands such as Ruedi Round 1 and 2 water sales are also included. (See Appendix F of <br />the Final PBO (U.S. Fish and Wildlife Service, December 20, 1999) for a listing of all projects <br />included in the backcast 1995 demand levels.) <br /> <br />~ <br /> <br />The Service requested that the baseline hydrology should be the Cl Scenario hydrology with the <br />existing flow related RIPRAP projects included and the Category 2 (i.e., future) depletions <br />excluded (Maddux, February 2, 1999 and clarification from Bob Muth to Leo Eisel, <br /> <br />p:\data\gen\Ocwcb\18133\report\phase-1 \chap-2.doc <br /> <br />2-6 <br />