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I I , ! I I I I I I . I I I I I I I I I I 002109 Hydrosphere's Colorado River Model December 29, 1993 Page 16 would continue, and did not consider impacts of severe climate change. Flexibility to rearrange priorities may be offered in future versions of the model if there is sufficient demand from our customers. Reservoir Operations The 14 reservoirs simulated in Hydrosphere's Colorado River Model contain a total active capacity of 61,375,000 acre-feet. One of the reservoirs, Starvation, is a composite reservoir representing an aggregation of eight actual reservoirs on the Duchesne River. Production of hydro-electric power is simulated at all reservoirs except Starvation, Taylor Park, and Ridgway. Although the McPhee and Navajo hydropower plants are still under construction, they are expected to be in operation within the next two years, and are included in the model. The active storage capacity of the reservoirs is modeled by dividing the storage capaCity at a reservoir into two parts, one representing target storage, the level of storage that the USBR attempts to meet to maintain power production and provide carryover storage (Schuster, 1988), and the other representing surplus (above target) storage. For some reservoirs, target storage is constant, while for others it varies from month to month. Releases from Lakes Powell and Mead are determined in a similar fashion to that in the CRSM model (Schuster, 1988). Comparison of CRAM and CRSM output for a 78-year simulation over the historic period showed that the two models give very similar monthly storage levels for Powell and Mead. A general description of operations at Powell and Mead is provided here -- more detail regarding operations is provided in the special operations sub- section. Releases from Powell are set to the "objective minimum release". The amount of the objective minimum release can be specified by the user but defaults to 8.23 maf per year as set out in the Operating Criteria. Releases in excess of the objective minimum release are made when additional releases are indicated by the rules governing equalization of storage between Powell and Mead, when surpluses are declared or when spills occur. Releases less than the objective minimum release may be made when Lake Powell is at dead storage. Under those conditions the provisions of the Colorado River Compact govern. In its baseline configuration, Hydrosphere's Colorado River Model treats the 8.23 maf delivery criterion as a delivery obligation and continues to call for that much water even after Lake Powell is at dead storage. Releases less than the objective minimum release will be made only when Lake Powell is at dead storage, when there is insufficient inflow to the reservoir to supply the 8.23 maf objective release and when all Upper Basin water rights junior to the Compact have ceased diverting. Rights in the Upper Basin that are not present perfected rights are subject to calls for water under the Compact. Releases from Lake Mead are based on three factors - forecasted inflows, requests for consumptive use releases, and flood control objectives. Over the entire year, a minimum amount of flood control space is maintained in Mead; this minimum is 1.5 maf in the baseline configuration. During the period from January to July, additional flood control releases are made, if necessary, on the basis of predicted inflow versus expected releases for consumptive use, with the goal of reaching August I with the minimum flood control storage space available. During the period from August to December releases are made as necessary to end up on January I with a specified target flood control space among Mead, Powell, Flaming Gorge, Blue Mesa, and Navajo Reservoirs (5.35 maf is the baseline assumption). Hydrosphere Resource Consultants 1002 Walnut Suite 200 Boulder, Colorado 80302