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Reservoir Operating Studies Elkhead Reservoir was modeled with a capacity of 13,700 af, as in the current conditions scenario. With the exception of the demand level, all modeling assumptions and reservoir operating rules were the same as those defined in the current conditions scenario. Results Water Deliveries Total basin water shortages are more frequent in this model scenario than in the current conditions scenario, occurring in 38 of the 53 years in the study period. Average annual total shortage is 1,598 of and the maximum annual total shortage is 15,721 of occurring in 1934. Most shortages are to agricultural demands though shortages to the coal-gasification plant are also frequent. Municipal shortages occur only in very dry years. ' Reservoir Levels Figure 2-2 shows the end-of-month contents of the three modeled reservoirs. An increase in storage draft is evident in all reservoirs, but is most noticeable in Elkhead Reservoir. In 1934, the power contract pool in Elkhead is nearly depleted and there are fairly regular drafts on that supply in other dry years. Stagecoach experiences somewhat greater drawdown in dry years, though the annual cycling is still dominated by winter hydropower and environmental releases. ' Instream Flow Conditions Modeled flows below the reservoirs are similar to those predicted under current conditions. Flows below Steamboat Lake increase slightly in the late summer as some deliveries are made to the Hayden Station. A similar increase is evident below Elkhead as industrial and municipal water users near Craig rely on storage releases to supplement direct ' flow water to meet their demands. Flows at Maybell are significantly reduced from current condition flows in the late summer through winter period. For example, median flows in September under current conditions are 112 cfs; with the 2040-level demands operating the median flow drops to 61 cfs. Occurrences of zero average monthly flow (an imprecise but useful indicator of flow conditions) increase from 5 under current conditions to 22 under future-without-project conditions. Table 2-7 presents the modeled 25th, 50th and 75th percentile flows at Maybell for the projected 2040 demand condition without enlargement of Elkhead Reservoir. Modeled median flows are lower than under current conditions for all months of the year; they are also lower than the recommended flows. Examination of the 75th percentile flows indicates that in one- fourth of Septembers, flows at Maybell would be less than 5 cfs; the 25th percentile indicates that September flows would be less than 130 cfs three-fourths of the time. Detailed results of this scenario can be found in Appendix F. 1 1 2-16