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Reservoir Operating Studies <br />Instream Flow Conditions <br />Modeled flows below the reservoirs are similar to those predicted under current <br />conditions. Flows below Steamboat Lake increase slightly in the late summer as some <br />deliveries are made to the Hayden Station. A similar increase is evident below Elkhead as <br />industrial and municipal water users near Craig rely on storage releases to supplement direct <br />flow water to meet their demands. <br />Flows at Maybell are significantly reduced from current condition flows in the late <br />summer through winter period. For example, median flows in September under current <br />conditions are 112 cfs; with the 2040-level demands operating the median flow drops to 61 cfs. <br />Occurrences of zero average monthly flow (an imprecise but useful indicator of flow <br />conditions) increase from 5 under current conditions to 22 under future-without-project <br />conditions. <br />Table 2-7 presents the modeled 25th, 50th and 75th percentile flows at Maybell for the <br />projected 2040 demand condition without enlargement of Elkhead Reservoir. Modeled median <br />flows are lower than under current conditions for all months of the year; they are also lower <br />than the recommended flows. Examination of the 75th percentile flows indicates that in one- <br />fourth of Septembers, flows at Maybell would be less than 5 cfs; the 25th percentile indicates <br />that September flows would be less than 130 cfs three-fourths of the time. Detailed results of <br />this scenario can be found in Appendix F. <br />Table 2-7 <br />Modeled Flows at Maybell at Projected 2040 Demand Level Without Project (cfs) <br />October 276 190 118 <br />November 334 245 198 <br />December 304 210 164 <br />January 270 201 163 <br />February 310 234 212 <br />March 681 471 370 <br />April 3,025 2,001 1,301 <br />May 6,964 5,716 4,007 <br />June 6,322 5,113 3,594 <br />July 1,702 947 399 <br />August 328 178 57 <br />September 130 61 6 <br />2040 Demand Condition with Enlargement Project <br />Key Assumptions <br />This final operating scenario adopts most of the basic assumptions of the previous <br />scenario but assumes the enlargement of Elkhead Reservoir and the revision of some reservoir <br />operating strategies related to that enlargement. Elkhead Reservoir is assumed to have a total <br />capacity of 44,900 af; this is the maximum practical capacity of an enlargement of the existing <br />2-18