WSP01056

• File Number: 8200.766
• Description: Gunnison River General
• State: CO
• Basin: Gunnison
• Water Division: 4
• Date: 2/13/1992
• Author: Unknown
• Title: Gunnison River Basin Planning Model - Existing Model Review
• Water Supply Pro - Doc Type: Report/Study

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SUMMARY DESCIUPTION
OF
EXISTING GUNNISON BASIN MODEL

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lNTRODjlCOON

This document is a summary description of the existing basin model based on the executive
summary and excerplS from Task Memorandum No.5 of me Colorado Water Resources and power De-
velopment Authority's ~hase 1 Study. A diagram of the model network and tables listing important data
and information supporting the summary are attached at the back of this document.

MODELING APPROACH

The basin model was developed using a network modeling system and runs on HJM-compatible
microcomputers. In the model, the basin is characterized as a network of links representing inflows,
stream reaches, diversions, reservoirs, and demands. The priorities placed on various links in the
network arc derived [n)ffi water rights considerations. These priorities control the allocation of water to
various uses represented in the model. Opera.ting rules {or various facilities are implemented through l
special computer code which adjusts the priorities assigned to specific links, such as those which l\
represent reservoir storage or releases.

The model operates on a monthly time step over a 1952.83 study period. In each month, the
model solves for an optimal allocation of available water supplies according to the priorities placed on
various Imks by the user. Reservoir carryover slOrage and lagged return flows are the connections be.
tween one month's solution and the nt:Xl. A diagram of the model network is attached to the back of
this document.

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Files of model inflows at 59 sites were derived by U.S. Bureau of Reclamation (lJSIJR) staIT in
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Grand Junction. These inflows are of three types: 1) virgin Oows, 2) gaged/flows, and 3) imputed reach
ga.ins. Vi-tWO flows at gaged shes were derived from historical Clow records' corrected for upstream reser.
voir operations, basin impons and exports, and irrigation depletiOnsl Historical irrigation depletions
were cstimalcd from consumplive use rates derived from the CRSS database, acreages oblaincd from the
USBN., the SCS, and the Gunnison County assessor, an.d ftom detailed operating studies of seleclt~d
ditches. Virgin (lows at ungaged sires were developed from virgin flows at "reference gages" corrected
for area and elevation differences; Table llisLS these reference gages.

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S11JDY PJiRlOD IIYDROLOGY

Gaged flows were used to represem inflows from the North and Smith Forks of the Gunnison
and the inflows to Ridgway Reservoir. Reach gains imputed from gaged flows were used to represent ac-
cretions along the Uncompahgre River abov~ the South Canal and along the Gunnison below Delta.

Return flows from ceflain water uses are also represented in the model as inflows; these 20 in-
nows arc compuled. internally by the modcJ based on user-supplied lag, factors. The specific rClUrn flow
factors V'....ry depending on type of water use and amount diverted and were adjusted during calibration.

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FEB 1 3 1992

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