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<br />l'I.fi f~ "s. <br />uu..~w <br /> <br /> <br />,. <br /> <br />SUMMARY DESCRIP110N AND REVIEW <br />OF <br />EXISTING GUNNISON BASIN MODEL <br /> <br />INTRODUCITON <br /> <br />This document is a s'umniary description and critical review of the existing basin model. It is <br />based on the executive summary and excerpts from Task Memorandum No. 5 of the Colorado Water <br />Resources and Power Development Authority's Phase 1 Study, on public comments received in the scop- <br />ing of the current planning model development project, and .on Hydrosphere's own technical review of <br />the model. A diagram of the model network and tables listing important data and infonnation support- <br />ing the summary are attached at the back of this document. <br /> <br />MODELING APPROACH <br /> <br />The basin model was developed using a network modeling system and runs on IBM.compatible <br />microcomputers. In the model, the basin is characterized as a network of links representing inllows, <br />stream reaches, diversions, reservoirs, and demands. The priorities placed on various links in the <br />netwo~k are; derived from water rights considerations. These priorities control the allocation of water to <br />various uses represented in the model. Operating rules for various facilities are implemented through <br />special computer code which adjusts the priorities assigned 10 specific links, such as those which <br />represent reservoir storage or releases. <br /> <br />The model operates on a monthly time step over a 1952-83 study period. In each month, the <br />model solves for an optimal allocation of available water supplies according to the priorities placed on <br />various links by the user. Reservoir carryover storage and lagged return lIows are the connections be- <br />tween one month's solution and the next. A diagram of the model network is attached.to the back of <br />this document. <br /> <br />S11lDYPERIOD HYDROLOGY <br /> <br />InDows <br /> <br />Files of model inllows at 59 sites were derived by U.S. Bureau of Reclamation (USBR) staff in <br />Grand]unction. These inllows are of three types: 1) virgin lIows, 2) gaged lIows, and 3) imputed reach <br />gains. Virgin lIows at gaged sites were derived from historicalllow records corrected for upstream reser. <br />voir operations, basin imports and exports, and irrigation depletions. Historical irrigation depletions <br />were estimated from .consumptive use rates derived from the CRSS database, acreages obtained from the <br />USBR, the SCS, and the Gunnison County assessor, and from detailed operating studies of selected <br />ditches. Virgin lIows at ungaged sites were developed from virgin flows at "reference gages" corrected <br />for area and elevation differences; Table 1 lists these reference gages. <br /> <br />Gaged lIows were used to represent inflows from the North and Smith Forks of the Gunnison <br />and the inllows to Ridgway Reservoir. Reach gains imputed from gaged lIows were used to represent ac- <br />cretions along the Uncompahgre River above the South Canal and along the Gunnison below Delta. <br /> <br />