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001260 .. Draft Task 7 Technical Memorandum .. Existinl!" Demands and Reservoirs - Baseline Condition The baseline demand level represents the maximum demand condition which could have occurred in 1989. The total consumptive demand for the baseline condition was estimated in Task 2 of the Study as approximately 121,000 af per year. These baseline demands can be grouped according to their priorities relative to the Juniper project. Senior Demands and Reservoirs: The majority of the depletions attributable to senior water rights are implicit in the gage-based (depleted) hydrology of the model. These "implicit seniors" include depletions associated with direct flow diversions and with existing reservoirs. A number of demands were represented explicitly in the model as increments to bring the depletions implicit in the gage up to a uniform baseline demand condition (the maximum demand occurring in 1989). For example, Craig municipal demand needed to be adjusted upward in earlier years of the study period (when there was little actual demand) in order to simulate current municipal demands over the entire study period. These "demand adjustments" are treated as being senior to all other demands explicitly represented in the model in order to be consistent with the use of gage hydrology. Included in these senior demands are demands 1 through 24, and demands 34, 37 and 38 (fable 2). The three existing reservoirs which were modeled explicitly (Stagecoach, Steamboat Lake, and E1kbead) are treated as having storage rights just senior to the Juniper Project rights. This was done to reflect existing subordinations of the Juniper Project to those reservoirs and to reflect the fact that the reservoirs have historically been allowed to fill without being called out by more senior rights in the basin. Junior Demands: Approximately 28,180 af of depletion presently occurs in the basin above the Little Snake River under water rights junior to the 1954 Juniper project. Approximately 24,200 af of these junior depletions were explicitly represented in the model. This 24,200 af represents all junior direct flow rights that result in depletions greater than or equal to 5 af per year and all reservoirs that deplete the basin by greater than 700 af per year. The remaining 4000 af of junior depletions result from many smaller irrigation diversions. These depletions were not explicitly modeled in order to simplify the aggregation of junior depletions throughout the basin, and to simplify the complilation of adjustments to gage hydrology. Existing junior demands are represented in the model as demands 50 through 55 (fable 2). In reality, juniors demands are spread throughout the basin with many located on small tributaries. In the model, the six aggregated junior demands were distributed along the mainstem of the Yampa River. Representing existing junior depletions explicitly in the model required adjustments to the gage hydrology on which the model was based. These adjustments reflected historical depletions by these junior demands. The adjustment was made by adding inflows to the model equal to the amount of the historical depletions of the junior demands occurring over the 53 year study period. The historical depletions were obtained from the Division 6 Engineers data- base on basin diversions. Future Demands - 2015 and 2040 Conditions Senior Demands and Reservoirs: All new reservoirs and reservoir enlargements represented in the model were treated as having rights senior to the Juniper Project rights. This reflects the assumption that portions of the Juniper storage right would be "peeled off" and transferred to these new storage facilities as part of any agreement for conversion of the Juniper rights to instream flow. As a result, these new storage facilities are allowed to fill 5 1 .~