8279

• UCREFRP Catalog Number: 8279
• Author: Brown and Caldwell.
• Title: Phase 1 Coordinated Facilities Water Availability Study for the Endangered Fishes of the Upper Colorado River.
• USFW Year: 2000.
• USFW - Doc Type: \
• Copyright Material: NO

Colorado River Decision Support System (CRDSS) and is a monthly water allocation and
accounting model with flexibility to become a daily model. It can be used to make comparative
analyses for assessing various water management policies and practices utilized in the
administration of a river basin. The model's operation is governed by basin hydrology, water
rights associated with diversion and storage structures, and the operating rules used for the
diversion and storage structures. StateMod uses four types of water rights: direct flow rights,
instream flow rights, reservoir storage rights, and operational rights. Water rights are sorted by
priority and river administration is simulated using the Prior Appropriation Doctrine.
StateMod was selected for this analysis for several reasons. It can be operated on a monthly time
step that allows for fast execution and a reasonable volume of output to be analyzed. The
simulations on a monthly time step will generally be adequate for assessing the impacts of
potential changes to water management policies within the basin. In those cases where the
impacts need to be examined at shorter time intervals, StateMod can be set up to run on a daily
time step. Input to the daily version of the model can be daily data for stream flow, diversion
demands, and reservoir targets, or a set of values for distributing the monthly data. Daily data
are available on the State's database and will be used in the daily runs of StateMod as discussed
below in the Baseline Hydrology section.
Routing of reservoir releases (lag times, etc.) is not included in either the monthly or daily model
because: (1) StateMod is primarily a planning model; (2) the additional detail required to
properly implement reservoir releases with a travel time component is not justified because the
system would have to include some kind of forecasting to know a reservoir release is required
before a reservoir demand occurs; and (3) the volume of water associated with a potential
under-release that occurs by ignoring travel time before a reservoir demand is known is offset by
the potential over-release that occurs after the demand is satisfied.
2.3.2 Baseline Hydrology
The PBO employs the hydrology from the C 1 Scenario developed for the PBO for investigative
purposes. In the C1 Scenario irrigation demands are calculated from average irrigation
efficiencies for the study period, 1975-1991. Irrigation efficiencies were calculated for CRDSS
based on historic data for the Colorado River Basin in Colorado (Moore, 1999). The
C 1 Scenario also includes "backcasting" of 1995 water year demands throughout the entire study
period for selected major structures. Average annual depletions for these existing demands are
used for every year. Depletions from demands that were in place for only a portion of the
1975-1991 1975 period were included in the C1 run for the entire study period. Depletions from
new demands such as Ruedi Round 1 and 2 water sales are also included. (See Appendix F of
the Final PBO (U.S. Fish and Wildlife Service, December 20, 1999) for a listing of all projects
included in the backcast 1995 demand levels.)
The Service requested that the baseline hydrology should be the C1 Scenario hydrology with the
existing flow related RIPRAP projects included and the Category 2 (i.e., future) depletions
excluded (Maddux, February 2, 1999 and clarification from Bob Muth to Leo Eisel,
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