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<br />Significant floods occurred in the South Boulder and Boulder Creek <br />watersheds in 1894, 1914, and 1938; and a somewhat smaller flood <br />occurred in 1938. Flooding occurred in the Lefthand Creek <br />watershed in 1864, 1876, 1894, 1921, 1938, 1949, and 1951. <br /> <br />The principal cause of flooding problems on the study streams in <br />the City 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, with the most <br />extensive flood occurring in 1894. This flood generally has been <br />designated as the 100-year flood; however, there is little <br />documentation of the flooding on streams other than Boulder Creek. <br />Flooding was widespread during the 1894 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 Twamile Creeks all overflowed <br />their banks according to newspaper accounts. On May 8, 1969, the <br />Boulder Daily 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 />Twamile Creek has frequently overtopped its banks with silt-laden <br />floodwater. The worst flood on Twamile Creek occurred in <br />September 1933, while others occurred in 1909, 1941, 1942, 1949, <br />and 1965. On August 19, 1965, the Boulder Daily Camera headline <br />read: "Twamile Canyon Gully Washer Spews Mud Across Broadway and <br />~nto Yards." The article stated that "Water cascading down <br />no~lly-dry Twamile Creek spewed mud across sections of Broadway <br />and silted yards and basements of 8 or 10 homes near Broadway and <br />Iris Avenue Wednesday afternoon." <br /> <br />Fou~le Canyon Creek has flooded occasionally, with notable events <br />occurring in 1916, 1941, and 1951. ~n 1916 and 1941, railroad <br />bridges were washed out (Reference 17). Localized 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 />Fou~le 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 damaged an addition to the Community <br />Hospital, which was under construction. <br /> <br />14 <br />