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o 0 3 :. : Qescription of Existing!MOdel 2 . , REPRESEN"L\TION OF,WATHllKIGHTS , Gunnison bas\n water tights are represented in'the model in one of two ways. Major water tights which Significantly influence river administration or which transfer water from one sub.basin to another are modeled ~dlvidual1y. These water rights, which are listed in Table 2, are modeled as diver- sions, consumptive use! demands; and return flows. Data for representation of water rights was obtairied , from the 1984 Stream Alpha Ust, the 1988 Water Rights Tabulation (electronic), line diagrams obtained from various sources, ~nd interviews with Water Commissioners and the Division 4 Engineer. , ,Most small irrigation water rights and a few small municipal and domestic tights are represented ..,;, as aggregated depletions rather than as diversions and return flows (depletions are the net of diversions ,;;: and" return flows). Th~se rights are aggregated by geographical location and by relative priority. Four '-. priority classes were defined using the priorities of major water rights to divide the classes. The small ir- . -I - - , _ . rigation decrees were 'then distributed into these classes based on their individual priorities. This geog- raphical and legal clas~ification of decrees resulted in definition of 212 separate demand points forrep- resentation of small irrigation water rights. Table 3 lists the priority intervals used in aggregating smaller rights. The depletion~ associated with each of these aggregated demand points were derived from Con- sumptive use calculations; surveys of irrigated acreage under specific ditches, diversion records, and detalled operating studies of selected ditches. The depletions are allocated between priority classes at . -. I each aggregation poin1 based on the distribution of decreed rights and historical diversions at each point. Historical dlve(slons at each point were allocated among the priority classes based on the as- sumption that diversiot.s take place flrsi under more senior water tights. The average allocation pattern so obtained was then psed to allocate total depletions at each point among the priority classes at that point (this reflects an assumption that each acre-foot diverted supported the same amount of depletion). I _ 1 , A number of iftstream flow watei' rights were represented in the model. The ewCB and pri. vately held instream fl'lw rights represented are listed in Tables 4 and 5. In addition, an instream flow right for 300 cfs, derived from ,the P&M water tight donated to The Nature Conservancy,was assumed to exist for the Black Canyon; this right was assumed senior to the Gunnison Tunnel 'power decree and served to protect Black Canyon augmentation releases (to insure a 300 cfs minimum flow) from Blue Mesa past the East Portlll. I , A few conditioOaI Water rights were represented in the model. These were selected from the many existing conditiollal decrees as beiIjg the most significant, either by virtue of their imminent devel- opment or their potenpal for impact on basin hydrology and water rights administration. The condi- tional decrees represented are listed in Table 6. ! Table 7 lists t~e overallrankings assigned to the various water rights and water rights groups represented in the model. .':Ni', OPERATIONS OF EXIS'pNG FACII.l11ES , The operating procedures of major existing or soon-to-be.developed water supply facilities are represented in the basiP model. Specific facilities and systems modeled in detail include the Wayne N. Aspinall Unit (formerly /mown as the Curecanti Unit), the Uncompahgre Project, the Bostwick Park Pro. ject, the Dallas Creek ~roject, and the Project 7 Water Authority. Smaller municipal and domestic sys. terns, such as the City 6f Gunnison and the Town of Crested Butte, were modeled simply as depletions because of their small size and the spatial and temporal proximity of diversion and return flow points.