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! I Final Draft - Preferred Storage Options Plan Southeastern Colorado Water Conservancy District June 8, 2000 The Winter Water Storage Program was simulated both with 40,000 af of firm storage and non-firm storage under existing policies and current spill priorities. When municipal Project water demands are fully realized, Winter Water is projected to spill 5 out of the 30 years, with an average annual spill of 7,449 af. Firm storage of Winter Water decreases the volume of spills, but does not decrease the number of years with spills. The decrease in the volume of Winter Water spilled does not result in a significant increase in Winter Water deliveries. The average annual deliveries increase from 22,116 afper year with non-firm storage to 23,489 af per year with firm storage. This is primarily because, even with firm storage, Winter Water can only be carried over until May I of the following year. This results in firm storage increasing the volume of Winter Water that is unused and released from Project storage. Modeling results indicate that non-Project water in Project space under re-operations generally spills 2 out of30 years, with average annual spills ranging from 884 afto 1,107 af. Generally, the volume of non-Project water spilled is less under firm Winter Water storage than non-firm Winter Water storage. During the years of non-Project spills, Project accounts for the re-operations entities are generally ful! except for the occasional year when non-Project water is spilled by Winter Water. During these years, instead of storing non-Project water in Project space through re-operations, the entities would need to find space in other storage facilities, exchange with other users, sell to other users, or allow the water right to remain unused and flow downstream. The simulation model was used for each of the five scenarios to evaluate impacts on stream flows and reservoir levels. A key finding of the model is that the location of storage, as reflected by the five scenarios (Table 3.1) has little effect on stream flow impacts (i.e., the impacts are very similar for all five scenarios). For the stream flow gages above Pueblo Reservoir (Figures 3.1 through 3.4), the impact analysis generally shows that stream flows increase compared with historical flow records during the summer months and decrease slightly during the winter months. Because the simulated ultimate annual demands are higher than under historical conditions, peak flows tend to be higher and there is a general increase in the volume of water moved annually from the upper basin to the lower basin. The Fountain Creek gage shows a general increase in annual flow due to the increase in return flows from Colorado Springs, Fountain, Wide field, and Security. The Colorado Division of Natural Resources has recommended to the USBR under a voluntary flow program that a minimum flow of250 cfs be maintained at the Wellsville gage throughout the year, and that a minimum flow of700 cfs be maintained from July 1 through August 15. The USBR has recognized the 2501700 cfs in-stream flow recommendations and operated the Project in recent years so that these flows are m GEl Consultants, Inc. 3-20 J.\PROJECTS\9906IIReporu\J>refc:rred SOP Final.wpd