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<br />Statistical analysis showed that the distribution of monthly runoff varies according to the total
<br />runoff during the year. During dry years, the runoff is low and most of the accumulated snow
<br />melts in May and early June. Therefore, during low flow years, the percentage of runoff in May
<br />is higher as compared to runoff during normal and high flow years. During normal and high
<br />flow years there is more snow than dry years and runoff from snow is distributed over a longer
<br />period of time, which results in a lower percentage of runoff during May. Leroux Creek runoff
<br />during May is 43 percent, 36 percent and 36 percent of annual runoff during dry, normal and wet
<br />years, respectively.
<br />
<br />As a result of the monthly distribution variability of runoff at Leroux Creek, the same criteria
<br />used in the 1986 PRC Report for selecting dry, normal and wet years was used for this study.
<br />The criteria are as follows:
<br />
<br />. Dry years are those with annual runoff less than the mean minus 42 percent times the
<br />standard deviation or 25,327 acre-feet.
<br />. Wet years are those with annual runoff greater than the mean plus 42 percent times the
<br />standard deviation or 48,184 acre-feet
<br />. Normal years are the years in which the annual flows are between the 25,327 acre-feet
<br />and 48,184 acre-feet.
<br />
<br />The average monthly and yearly runoff during dry, normal and wet years in Leroux Creek is
<br />shown in Table 4. In addition, the standard deviation and the monthly distribution of runoff as a
<br />percentage of total annual runoff are also summarized in Table 4.
<br />
<br />Table 4
<br />Monthly Runoffs for Low, Normal and High Flow Years for Leroux Creek
<br />(Hydrologic Year)
<br />
<br />Month n 12 1 2 3 4 5 6 7 8 9 10 Annual
<br /> Average Monthly Runoff (ac-ft)
<br />lory 446 344 307 298 433 2,601 11,007 4,649 1,803 1,528 1,058 854 25,327
<br />[Normal 617 389 348 321 469 2,789 13,124 10,728 2,973 1,981 1,459 838 36,036
<br />Wet 650 394 377 368 548 2,867 17,522 16,148 3,969 2,480 1,670 1,192 48,184
<br /> Standard Deviation
<br />Dry 115 88 84 69 III 1,584 2,878 2,434 292 305 318 330 4,826
<br />Normal 395 100 115 76 130 1,882 2,145 4,785 915 537 671 410 5,708
<br />Wet 389 96 82 99 244 1,974 5,300 6,471 2,618 978 638 941 8,472
<br /> Monthly mow asPer~ntage of Annual
<br />Dry 1.76 1.36 1.21 1.18 1.71 10.27 43.46 18.36 7.12 6.03 4.18 3.37 100
<br />Normal 1.71 1.08 0.97 0.89 1.30 7.74 36.42 29.77 8.25 5.50 4.05 2.33 100
<br />Wet 1.35 0.82 0.78 0.76 1.14 5.95 36.36 33.51 8.24 5.15 3.47 2.47 100
<br />
<br />The analyses detailed above were also conducted for runoff at Surface Creek. It was determined
<br />that a wet year in Surface Creek corresponds with a wet year in Leroux Creek and a normal
<br />
<br />~.~
<br />
<br />-5-
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