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o () 1167 30 In order to. maintain consistency, all demand increments added to the model to adjust gage hydrology to current conditions should likewise be considered senior to the Juniper right. To do othervvise would mean, for example, that thermal-electric depletions from 19jO to 1974 would be junior to Juniper and depletions from 1975 to 1982 (which are embedded in gage hydrology) would be senior. Accordingly, all demand arcs representing such adjustments are assigned IJriorities higher than the priority assigned to the T&E instream now right. Similarly, all existing reservoirs represented in the model are given storage priorities higher than the Juniper right; this assumption is justified by the subordinations of the Juniper rights discussed earlier. At this time the relative priorities between demands that are considered senior to Juniper are differentiated on the basis of priority rcbtive to the Maybe-II Canal. Differentiation of these priorities is necessary only if there is insul'ficient supply available to meet them all. If differentiation is necessary, the relative priorities are determined from the absolute water rights that support thos..:" demands. Demand arcs representing future demand increments were assigned priorities lower than the Juniper right. This rellects the conservative assumption that all future demands are dependent on junior water rights. At this time relative ranks of future demands arc differentiated only in an order to access specific storage contracts in existing reservoirs in a prescribed order. It is important to remember that differentiation of priorities is necessary only if there is an inadequate legal and physical supply to meet all demands (the legal constraint could be eliminated if the subordination were sized to protect all future uses). General Reservoir Operations Three existing ieservoirs are operated in the Yampa River Basin Model: Stagecoach Reservoir, Steamboat Lake, and Elkhead Reservoir. The operations of all other existing reservoirs are assumed to have negligible effect on flows below Stagecoach Reservoir eitller because of their small size or because of their mode of operation. The model network is currently configured to represent nine reservoirs. Six of these reservoirs are currently undeveloped but re~nain in consideration as possible future projects. These reservoirs have effectively been turned off in the first sets of model runs by constraining the capacities of storage arcs and evaporation to zero now. Reservoir evaporation and storage carryover are automated in the CRAM modeling system. Storage and release operations are driven by the relative priorities between reservoirs and demands. If demands are ranked higher than reservoirs, 'the model will allocate water to demands before allowing reservoirs to fill and will draw water out of storage to satisfy demands unmet by 'natural flows. If reservoirs are ranked higher than demands, reservoirs will be filled first and demands will be unable to draw water out of st()rage: the reservoirs will subsequently store only enough water to make up evaporati~::m. In practice what is usually dCsire'd is an interleaving of storage and demand priorities in order to simulate the operation of a conservation pool and a recreation pool. The conservalion pool should be emptied to meet unsatisfied demands but the recreation pool should not. This is accomplished by the use of link arcs representing storage volume targets. The diseussion below describes how the basin model accomplishes reservoir operations in general sense. This discussion is followed by a description of the operating rules that were assumed for the three existing reservoirs. The operations of both existing and proposed reservoirs are simulated through the use of a common construct of network arcs. A hypothetical reservoir structure is shown as Figure 4~3. Target arcs appear as parallel ares labelled "Tl, T2, 1'3" in the reservoir sub-network. The sizes (capacities) and relative priorities of these target are set according to assumed ownership accounts in' the reservoir.