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'.:.;. O n ~ 1: ~cutive Summary U~........u rights in the basin and discussed issues related to transfer of portions of the Juniper righl to instream flow use. s "i Based on this review it was determined that all existing uses in the basin, as weB as the filling of existing reservoirs, could be considered senior to the Juniper rights by virtue of their individual water rights priorities or the subordination of the Juniper rights. Among these senior uses, only the diversions by the cities of Craig and Steamboat Springs could be considered senior to the Maybell CanaL The deci. sion to represent all existing uses as having senior priorities meant that the basin model could be devel. oped using gaged rather than virgin hydrology; by leaving existing depletions in the hydrologic data set the senior status of existing uses is implied since no model operations could affect those uses. ..-~ "," While some basin water users hold rights senior to the Juniper Project that could be used to support future development, it was decided that future uses should all be considered junior to the juniper rights to be conservative. The relative priorities to be assigned to future reservoir storage is an open question. In the model, these storage rights were assumed to benefit from subordination of the juniper rights or to be exercised under a transferred portion of the juniper rights. Either assumption results in treating those reservoirs as being senior to the Juniper rights. Two general mechanisms through which the Juniper rights might be transferred to instream flow use while protecting anticipated future water needs of-the basin were reviewed. These were: 1) the sub. ordination of the Juniper rights to all future demands that are within the subordination, and 2) the transfer of portions of the juniper right to new storage facilities which could. in turn, serve the future demands. It was determined that the basin model should support quantitative evaluation of both these mechanisms. Additional mechanisms including alternative reservoir operations may be further reviewed in the future. Basin Hydrology and Data Development Streamflow records for all gages in the basin were compiled and reviewed for potential use in deriving model inflow data sets. It was determined that the model should run on a monthly time step for the 1930 to 1982 period to facilitate comparison with the USFWS modeling work. B,ased on the water rights review it was also determined that the model could be based on gaged rather than virgin flow hydrology. ,3 '. Based on the demand projections of Task 2, the reservoir site evaluations of Task 5; and the review of basin water rights, the points at which model inflow data were required were identified. A to. tal of 29 inflows (excluding return flows) were so required, These inflows and reach gains were derived wherever possible by mass. balance calculations using gage records. Missing or incomplete gage records were reconstructed using regional analysis techniques. These techniques relied heavily on the records for the Steamboat Springs and Maybell gages, the two most complete streamflow data points in the basin. In some cases, area.elevation adjustments were used to define inflows that could not be com. puted directly from gage records, ";~ :, ,:; Development of Basin Model "0 The basin model is an application of a network modeling system known as the Central Resource Allocation Model (CRAM). The various inflows, river reaches. water storage and conveyance structures, and water rights of the basin are represented as a network of arcs and nodes. The capacities of the arcs define the physical capacities or decree limits associated ~th flows in those arcs; the unit values1 or ranks, assigned to the various arcs reflect the water rights or operational priorities for allocating flows to those arcs. In each monthly time step the model allocates the inflows for that month to the various arcs representing diversions, storage, and streamflows. If inflows are in excess of diversion and storage re- quirements, the model routes excess flows downstream and out of the network. ~ .' 'I: , ,'c ~\