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. 002545 . Table 2-11 Average Monthly Flows for the Arkansas River and Fountain Creek Dischoroelcfsl Arkansas River Fountoin Creek Abo,," Pueblo Moffot Street Neor Pueblo Neor Pueblo Month Go~e Gope Gope Gope Januarv 138 87 317 67 Februarv 205 156 284 72 March 373 314 243 69 Aoril 676 591 387 93 Mav 1,157 1,140 1,086 202 June 2,333 2,318 2,\32 \49 July 1,658 1.660 1.413 85 AU2:ust 1,026 929 919 . 132 Se;;tembcr 476 379 427 50 October 323 255 349 54 November 269 215 367 67 December 154 108 338 64 Period of Record 1989-1999* 1989-1999 1895-1975 1922-1999** * A voiloble Period of Record 1965-1999; truncated for comporison ** Record is interminent: 1922-1925,1940-1965,\971-1999 Source: USGS Online, 2000 The decrease in flows belween the Above Pueblo and the Moffat Street gages shows the effect of the diversions in the study area. Since most of the major diversions here are year round, every month of the year shows a drop in flows between these gages. Data from the Near Pueblo gage was compared to post 1975 data from the Above Pueblo gage to show the effects of the Pueblo Dam on the hydrology of the study area. Average monthly flows for the pre- and post-darn time periods are presented in Figure 2-5. Operation of Pueblo Reservoir and the Fryingpan-Arkansas Project have affected the hydrology of the river below the dam. Figure 2-6 shows the flow duration curves developed for the pre- and post-dam periods of record. This shows that the occurrence of extreme low flows (below 50 cfs) has actually decreased with the dam control; however low flows, greater than 50 cfs to about 300 cfs, show an increase in occurrence. The dam has reduced the frequency of occurrence of extreme low flows; however, the Winter Water Storage Program (WWSP) has reduced the sustained winter flows, as a portion of the winter flow is stored for release during the irrigation season. The peak flows of the river have also been greatly reduced; however the release of the stored peak flows and the WWSP increase the flows during the remainder of the irrigation season. The peak discharges associated with return intervals ranging from the 1.25-year through 500- year were determined at these gages. The flood peaks were based on Log Pearson's type III analyses (WRC, 1981). Table 2-12 presents the return period floods for each gage and interpolated data for Wildhorse Creek. A generalized skew of -0.1 with a weighting factor of 0.302 and a station skew of 0.11 were used for all analyses based on Bulletin 17B, Plate I (WRC, 1981). The 100-year flood peak for the Above Pueblo gage, which is representative of Arkansas RIver Flshen~s HJbltJI Res[OTJllOn, Pueblo, Colorado Final Ecosystem ReSloratlon Reopon and Environmental Assessment 11.33 Chapter II. EnVironmental Seltlng September 200 I