FLOOD04722 - Laserfiche WebLink

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I I I I I I I I I I I I I I I I I I I SECTION V RUNOFF The storm described above produced a flash flood of short duration and high peak discharge which caused the failure of the Colorado and Southern Railway bridge over Frijole Creek. Data are insufficient to establish whether the flood washed the bridge out before or after the train arrived at the bridge. The most significant damage caused by the storm was to the Colorado and Southern Railway bridge. Damage was also caused to other county roads and bridges, and a number of bridges were washed out by the flood. U. S. Highway 160 bridge was closed for several hours by the flood- waters. Erosion damage to lands was considerable in the upper reaches of the basin. Appendix B contains representative photographs of the flood which illustrate the erosion damage and some of the damage to the bridges. PEAK DISCHARGE Two methods of computation were used to determine the peak dis- charge of runoff from the storm. The first combined the estimated flow through the bridge opening using the contracted-opening method and weir flow over the railway. This method indicated a discharge between 40,000 and 50,000, cfs including approximately 5000 cfs in weir flow over the railway tracks. The tracks served as a dam, with the backwater effect forming a reservoir on the upstream side. Figure 4 is a profile along the railway tracks, and illustrates the high water marks both south and north and the estimated depth of water over the tracks during peak flow. A second and more reliable estimate of discharge was made at a l200-foot reach of generally straight channel approximately one-half mile downstream from the bridge site using the slope-area method. The discharge in Frijole Creek determined by this method was about 48,000 cfs. The flood through this channel reach was contained on the north side of the creek, as evidenced by clear and well defined high water marks along the hillside above the stream. The flood was not entirely V-l