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TABLE 4.2 MEAN, MINIMUM, AND MAXIMUM AVERAGE DAILY FLOWS BY MONTH ON THE GUNNISON RIVER AT DELTA, CO FOR 1976-1999. Month Daily Flow Daily Flow Daily Flow Exceedence for Mean Daily Flows (cfs) (cfs) (cfs) (cfs) Minimum Mean Maximum 0.1 0.2 0.5 0.8 0.9 January 299 1630 3700 2991 2385 1481 749 565 February 421 1673 3740 3285 2444 1578 778 617 March 315 1957 5350 3689 3084 1818 809 613 April 282 2532 9120 4806 3913 2085 1091 675 May 299 4776 19,200 9071 7164 4313 1591 896 June 210 4284 20,300 9125 7042 3136 1284 710 July 244 2263 14,100 5175 3341 1310 491 366 August 208 1213 5,100 2296 1708 1097 496 357 September 289 1248 4,390 2125 1788 1123 700 550 October 333 1421 5,030 2612 1987 1272 722 574 November 395 1544 3,730 2698 2393 1446 700 563 December 355 1621 3,280 2598 2393 1446 700 563 TABLE 4.3 FREQUENCY ANALYSIS FOR WATER YEARS 1977-1998 ON THE GUNNISON RIVER AT DELTA. CO Return Periods Peak Flow, cfs !Years) 1.25 3,460 2 6,470 5 11,600 4.4 Summary of Design Flows Several critical design flows are considered to develop a range of flows for conducting the hydraulic analysis. One low flow scenario analyzed is 350 cfs, which represents the flows exceeded 90% of the time in August. By coincidence 350 cfs is also equal to the 90% exceedence value in July. All other months have a 90% exceedence that is greater than 350 cfs, including September and October. The lowest flow of all the years analyzed (1974 to 15 I I I I I I I I I I I I I I I I I I I