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17 <br />The Service's earlier flow recommendations for spring identified the magnitude <br />and frequency of a range of minimum peak flows and the mean monthly flows <br />capable of producing these peaks and of maintaining the natural shape of the <br />hydrograph. Refinement of these earlier flow recommendations for spring was <br />based on the results of new streambed monitoring studies. The results of one <br />study showed that the spring runoff in 1993, which peaked at 25,900 cfs, was <br />capable of moving coarse bed materials thereby winnowing accumulated fines <br />from the channel substrate. Osmundson et al. (1995) suspected that the <br />earlier recommended peak of 23,500 cfs would also be capable of moving bed <br />materials. The results of another study showed that a spring runoff with a <br />peak of about 12,900 was capable of flushing accumulated fine sediments from <br />the bottoms of backwaters thereby restoring their depth. Based on this <br />information, the Service developed recommended peak spring flows: <br />Tar4et Peak Spring Flows in the 15-mile Reach: <br />>23,500 cfs (5 in 20 years) <br />21,750 cfs (5 in 20 years) <br />16,700 cfs (6 in 20 years) <br />12,900 cfs (4 in 20 years) <br />The Service's 1995 year-round flow recommendations are summarized in Table 1 <br />as mean monthly discharges. Spring (April-July) recommendations are further <br />subdivided into 10-day increments and are reported in Table 2 as volumes of <br />water needed for each of twelve 10-day time periods. Variation in <br />precipitation levels from year to year is taken into account and <br />recommendations are provided for years of high, above-average, below-average, <br />and low snow fall. With the exception of winter, recommendations are for <br />flows considerably lower than historic levels but somewhat higher than recent <br />levels. ~~ <br />2~ <br />~, <br />/`2~fi~ ~ ~ sue,-e.~~ <br />~. c/' . ~. ~'~6~z! <br />~,-~ ~ ~r/~/g6 <br />