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<br />Significant floods occurred in the South Boulder and Boulder <br />watersheds in 1894, 1914, and 1938; and a somewhat smaller <br />occurred in 1938. Flooding occurred in the Lefthand <br />watershed in 1864, 1876, 1894, 1921, 1938, 1949, and 1951. <br /> <br />Creek <br />fl ood <br />Creek <br /> <br />. <br /> <br />The principal cause of flooding problems on the study streams in <br />the Ci ty of Boulder is intense localized thunderstorms. Because <br />the headwaters of these streams are below 9,000 feet, snoWMelt does <br />not influence the peak discharges. <br /> <br />Numerous floods have occurred in the Boulder area, wi th the most <br />extensive flood occurring in 1894. This flood generally has been <br />designated as the lOO-year flood; however, there is little <br />documentation of the flooding on streams other than Boulder Creek. <br />Flooding was widespread during the l894 flood, and nearly all <br />bridges in the city were washed out. <br /> <br />The most extensive flood since 1894 occurred on May 7 and 8, 1969. <br />This flood was also the most expensive, with damages estimated to <br />be $325,000. Bear Canyon, Skunk, and Twomile Creeks all overflowed <br />their banks according to newspaper accounts. On May 8, 1969, the <br />Boulder Dailv Camera reported that "motorists were still being <br />routed around the intersection of Table Mesa Drive and Broadway, <br />where Bear Creek raged out of its banks, flooding the entire area <br />Wednesday." (See Figures 1 and 2 for photographs of flooding on <br />Bear Creek.) <br /> <br />Twomile Creek has frequently overtopped its banks with silt-laden <br />floodwater. The worst flood on Twomile Creek occurred in September <br />1933, while others occurred in 1909, 1941, 1942, 1949, and 1965. <br />On August 19, 1965, the Boulder Dailv Camera headline read: <br />"Twomile Canyon Gully Washer Spews Mud Across Broadway and Into <br />Yards." The article stated that "Water cascading down normally-dry <br />Twomile Creek spewed mud across sections of Broadway and silted <br />yards and basements of 8 or 10 homes near Broadway and Iris Avenue <br />Wednesday afternoon." <br /> <br />Fourmile Canyon Creek has flooded occasionally, with notable events <br />occurring in 1916, 1941, and 1951. In 1916 and 1941, railroad <br />bridges were washed out (Reference 17). Local ized flooding along <br />the lower reaches of Fourmile Canyon Creek occurs frequently, <br />according to local residents. (See Figures 3 and 4 for photographs <br />of flooding on Fourmile Canyon Creek.) Damages and losses along <br />Fourmile Canyon Creek have generally been low, because the area is <br />primarily undeveloped. <br /> <br />Significant flooding along Goose Creek occurred in August 1951 and <br />July 1954. The 1954 event dalDaged an addition to the Community <br />Hospital, which was under construction. <br /> <br />. <br /> <br />14 <br />