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<br /> <br />1 <br /> <br />i. <br /> <br /> <br /> <br />1 <br /> <br />li <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br />shazed. The five workshops were held on April 25, May 31, June 28, August 7, and September <br />9,1996. Complete meeting notes, copies of material presented, and attendance lists for each of <br />the meetings are included in the Appendices. <br />Flow Analysis of the Duchesne River <br />An examination of impacts, with changing operation on the Duchesne River, was done by <br />dividing the record into two periods (pre-1970, post-1970) to develop statistics for each <br />period. The pre-project period was assumed to represent historical flow regime, and the <br />post-project period was assumed to reflect current flow regime with increased diversions <br />from such projects as CUP. There is no defined date when the flow regime changed from <br />historical flow regime, because the change was incremental. Major changes occurred with <br />the CUP project coming online in 1970. Thus, the pre-project and post-project periods are <br />assumed to be pre- and post-1970, respectively. To assist in determining pre-project flows <br />and the effects of longer term record, the Myton gauge was used to extend the flow record <br />of the Randlett gauge to earlier periods with less development. <br />Extending the flow record for the Randlett gauge was accomplished by making a linear <br />correlation with the Duchesne River at Myton stream gauge. The extended record shows <br />(approximately) a 20 percent increase in pre-project average flows with an average volume <br />of 533,700 acre-feet. Flow statistics for the various periods are summarized in the table <br />below. <br />Table ES-1 <br />Duchesne River at Randlett <br />AVERAGE MONTHLY FLOW (AC-FT) <br />Period Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Annual <br />1912-1994 22,739 24,932 26,516 25,401 25,589 32,242 30,805 87,878 134,476 35,295 16,177 16,882 478,932 <br />1912-1969 23,341 26,093 28,187 26,910 27,027 33,813 35,873 106,638 151,033 38,517 17,891 18,410 533,732 <br />1970-1994 21,342 22,238 22,642 21,901 22,253 28,598 19,048 44,355 96,064 27,820 12,201 13,336 351,796 <br />AVERAGE'MONTHLY FLOW {CFS) <br />Period Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep <br />1912-1994 370 419 431 413 457 524 518 1,430 2,260 574 263 284 <br />1912-1969 380 439 459 438 483 550 603 1,735 2,539 627 291 309 <br />1970-1994 347 374 368 356 397 465 320 722 1,615 453 198 224 <br />Review of USBR Pre-Development Flows <br />An analysis of the Duchesne River has been performed by the USBR to determine <br />"Pre-Development Flows" of the Colorado River Basin. These flows were developed by the <br />USBR for the whole Colorado River Basin in an attempt to develop virgin river flows. <br />These were developed primarily to be used in compact issues on the Colorado River among <br />the states. They historically have been updated every 5 years. The average yearly flow for <br />the period of record from 1912-1990 is 768,000 acre-feet. This compares to an average yearly <br />flow of 498,000 acre-feet for the same period of record at the Randlett gauge, or a long-term <br />SLC113410TREPTI.DOC ES - 2 <br />