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<br />Table 6 <br />Summary of Pertinent Discharges <br />for the Big Thompson River Basin <br /> <br />Locat I on <br /> <br />Drainage <br />Area <br />(sq. mi.) <br /> <br />10-Year <br />01 scharge <br />Peak <br />(c.f.s.) <br /> <br />50-Year <br />Discharge <br />Peak <br />(c.f.s. ) <br /> <br />100-Year <br />Discharge <br />Peak <br />(c. f.s.) <br /> <br />500-Year <br />Discharge <br />Peak <br />(C. f .s.) <br /> <br />BIG THOMPSON RIVER <br /> <br />Upstream limit 5,000 12,100 19,000 40,000 <br />of study <br />Interstate 4,300 8,800 11,500 21,000 <br />Highway 25 <br />Larimer-Weld 3,600 7,600 10,000 18,500 <br />County Line <br /> LITTLE THOMPSON RIVER <br />Upstream limit 101 3,300 6,600 8,800 17,000 <br />of study <br />Dry Creek 143 2,850 5,800 7,500 '13,400 <br />Larimer-Weld 2,800 5,500 7,200 12,800 <br />County Li ne <br />FREQUENCY <br /> <br />i, <br /> <br />The 500-year flood is not the largest flood that can <br />occur, but the probability of larger floods is remote. As can be <br />seen from the gaging records for the Big Thompson and Little <br />Thompson Rivers, discharges smaller than either the 100-year or <br />500-year floods are much more common. Large floods, however, can <br />happen; this was clearly demonstrated by the Denver area floods <br />of 1965, the June 1972 flood at Rapid City, South Dakota, and the <br />August 1976 flood in the Big Thompson canyon. <br /> <br />Flooding can occur with relatively little discharge in <br />the event of channel blockage caused by debris or Ice. In these <br /> <br />23 <br />