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:.~.~.;- C"j f:~.' .{~ e Project Operations, but in general, diversions and depletions increase with the amount of water available in the Animas River, as shown in Figure 3. On a monthly basis, the greatest withdrawals from the Animas River usually occur during the spring runoff, when the full pumping plant capacity is used to fill Ridges Basin Reservoir. The impacts of the project can be determined from the operation study. The flow of the Animas River downstream of the Durango Pumping Plant would generally be decreased through most of the year. During the months of April, May, and June, the flow would decrease by an average of 315 cfs, or 17 percent; during the remainder of the year flows would decrease by an average of 130 cfs or 33 percent. About 11 percent of the time, most often in the late irrigation season during August and September, the pumping plant would not be operating because either the reservoir was full, the river flow was below 225 cfs during the period April through September or 125 cfs during the period October through March, or maintenance was being performed in the plant. During these times, the flow in the river to Aztec would be increased because of M&I return flow from Durango and occasional M&I releases from Ridges Basin Reservoir. . Wet, normal and dry years were chosen from the operation study to accurately assess the current impacts of project construction. Releases from Navajo Dam alter the timing of San Juan River flows and affect the calculated impacts of the project. Dam releases vary considerably even with the same annual volumes, so caution must be exercised in interpreting these three types of hydrologic conditions. Monthlr flows in the Animas River at Durango for these three scenar~os are listed in the following table and are plotted in Figures 4 through 6: Representative monthly flow with and without the project-- Animas River below Durango Pumping Plant (Unit-cfs) Wet Year (1973) Normal Year (1966) Drv Year (1977) without with without With without with Project Project Project Project Project Project January 326 129 291 128 151 130 February 308 129 275 128 146 135 March 407 180 447 244 137 140 Apr i1 825 635 877 622 247 259 May 3,449 3,381 2,309 2,108 462 392 June 4,627 4,234 1,738 1,321 682 425 July 2,360 1,932 707 421 324 285 August 692 305 375 306 400 239 September 461 230 239 225 319 254 e October 288 129 224 140 221 151 November 206 127 203 126 185 126 December 192 127 213 132 171 127 5