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<br />17 <br /> <br /> <br />; <br /> <br />south approach, leaving a gaping hole in the roadway." <br />A companion picture shows timber shoring along the streamward <br />face of the levee north of the channel just downstream from Sunset <br />Drive. An explanatory statement read in part: "*** /the levee/ <br />continues to hold despite high water in the river which formerly <br />flooded over the area in South Longmont". <br />From the pictorial evidence supplied by the photographs in <br />figures 4-6 and from computations that have been made of the hydraulic <br />capacity of St. Vrain Creek, it appears that the recurrence interval <br />of the 1894 flood is substantially greater than 50 years, that the <br />recurrence interval of the 1921 flood is about 50 years, and that <br />the recurrence interval of the 1957 flood may be about 25 years. <br />It is emphasized that these recurrence intervals are only very rough <br /> <br />estimates, and cannot be used to assign discharges to those floods. <br /> <br />Damaging floods on St. Vrain Creek at Longmont, with the <br />possible exception of those of 1864 and 1844, invariably have been <br />associated with heavy rains in the Plains region. Snowmelt has <br />been a factor in most of the floods, b~t snowmelt alone has not <br />caused noteworthy floods in the study area, at least since 1864. <br />Consideration of the floods of 1894, 1919, and 1941 illustrates <br />this point. The peak discharges of these three floods at Lyons <br />were very nearly equal; the flood of 1894, augmented by heavy rains <br />in the plains, was the greatest known at Longmont; the floods of <br /> <br />1919 and 1941, which occurred when there was little or no rain <br />