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<br />mph 05 ft/sec) or 16 km/h (4.5 ,,/sec.). Although this is somewhat greater <br /> <br /> <br />than the velocity reported by Mr. Vogt, it is to be expected because the <br /> <br /> <br />property is nearer to the mouth of the channel and the surface gradient <br /> <br />in this area is roughly 140. Flow depth at this location was at least <br /> <br />5 ft 0.5 m). In both locations. large boulders "ere transported by the <br /> <br />flows, as discussed below,. although it appears that flood waters which <br /> <br />followed each debris-flow surge dispersed the debris and removed some of <br /> <br />the finer sediment. <br /> <br />Good correlation with these velocity estimates was made by comparing <br /> <br />them to calculations of debris-flow velocities made from data collected <br /> <br />in the channels. The calculations were not based on any of the commonly <br /> <br />used hydraulic engineering formulas (such as the Manning formula) because <br /> <br />such formulas cannot be applied to the flow of debris. Details of the <br /> <br />calculation method are given in the Appendix; the results of the calculations <br /> <br />at various locations in the channels are given in Table 2. <br /> <br />Although the velocities and diseharges given in Table 2 are only approximate, <br /> <br />the range reported appears to be rea::;onably consistent in view of the observations <br /> <br />of residents of the area. For e"ample, the average velocity of 16.7 ft/sec <br /> <br />(5.0 m/sec) obtained from the three cross sections in the lower 500 ft <br /> <br />(150 m) of Gulch A is about twice the velocity estimated by Mr. Vogt near <br /> <br />- 24 -. <br />