9600

• UCREFRP Catalog Number: 9600
• Author: Brown and Caldwell.
• Title: Phase 2 Coordinated Facilities Water Availability Study for the Endangered Fishes of the Upper Colorado River - Final Report.
• USFW Year: 2003.
• USFW - Doc Type: \
• Copyright Material: NO

2.3 ASSUMPTIONS AND ANALYSIS PROCEDURES
2.3.1 Model
Evaluation and analysis of the various alternatives was performed using StateMod, the State of
Colorado's Stream Simulation Model by determining the effects of the various alternatives on the nine
major reservoirs in the Upper Colorado River Basin (see Table 1). StateMod was originally developed
for the 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.
1

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1

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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- themonthly data. _ --
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: C1 Data Set
2.3.2.1 C1 Data Set. The PBO employs the hydrology from the C1 Data Set developed for the PBO
for investigative purposes. In the C1 Data Set, 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 Cl Data
Set 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 period were
included in the C1 Data Set for the entire study period. Depletions from new demands such as Ruedi
Reservoir 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.]
PAData\GEN\CWCB\19665\Report Phase 2\FinalReport9.03\Final_CFOPS_Report(9-03).doc 19