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<br />is an average of larger and smaller flows over the 14-day period. The results reveal that
<br />during the post-project period the percent exceedance of the 14-day average for 1,800 CFS
<br />and 3,000 CFS was approximately 46 percent and 29 percent, respectively.
<br />Development of Randlett Flow Data to Early 1900s
<br />Extension the flow record for the Randlett gauge was accomplished by making a linear
<br />correlation with the Duchesne River at Myton stream gauge. The Myton gauge is located
<br />approximately 16 miles upstream of the Randlett gauge. The period of complete record for
<br />the Myton gauge is from 1912 to 1994. A coefficient of determination or RZ of 0.972 was
<br />calculated for the correlation of concurrent monthly flows from 1943 to 1969, shown in
<br />Figure 4-16. Using the correlation, the Randlett flow record was extended by calculating
<br />monthly flows from 1912 to 1942. The extended record shows (approximately) a 20 percent
<br />increase in pre-project average flows with an average volume of 533,700 acre-feet. The
<br />extended flow record for Randlett is shown in Tables 4-6 and 4-7, and in Figure 4-17. Flow
<br />statistics for the various periods are summarized in the table below.
<br />Table 42
<br />Duchesne River at Randlett
<br />AVERAGE MONTHLY FLOW (ACRE-FEET)
<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 Annual
<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 />Hydrologic Effects
<br />The mean value from one period to another is subject to distortion of extreme values that
<br />may have occurred in a period due to hydrological effects. The hydrologic effects are the
<br />result of natural hydrological cycles independent of development. An attempt was made to
<br />remove the hydrological effects from the Duchesne River at Randlett, for the post-project
<br />period, so that an accurate estimation of project effects from diversions and depletions
<br />could be made. To remove the hydrologic effects, a correlation with other stream gauges
<br />not affected by diversion or depletions was made with the extended Randlett flow record.
<br />After the analysis was performed it was concluded it did not significantly add to the study
<br />and was not included.
<br />SLC~13410TREPTI.DOC 5.3
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