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<br />A <br />B <br />C <br /> <br /> TABLE 1 <br />Total Basin Debris Basin Debris Basin Debris <br />Area (A) Area Gradient Volume (K) A/K <br />[acres(ha)] [acres(ha)] ~eesL._ [ac-ft(m3)] Ratio <br />--- <br />78 (32) 27 (11) 25-40 270(3,33xl05) 0.29 <br />96 (39) 6 (2.5) 25..40 94(1.l6xl05) 1.0:1 <br />124 (SO) 9 (3.5) 25-40 87(1.07xl05) 1.43 <br /> <br />Basin <br />Name <br /> <br />Note: The ratio A/K is an index related to the amount of water runoff <br />available per unit volume of available metastable debris. All <br />A/K ratios here are "small" and suggest (1) a continuing potential <br />for destructive flows, and (2) a tendency for the basins to <br />produce viscous debris flows rather than water floods. <br /> <br />The debris source areas are located in the lower part: of e.ach basin. When <br /> <br />comparing basins of similar Burface infiltration potentials, it is intuitive <br /> <br />that the larger basins will tend to produce thE! grE!ater volumE'" and discharges <br /> <br />(volume/time) of floodwaters. Ho"ever, unstable debris volume must also <br /> <br />be considered when evaluating debris-flow potential or susceptibility. <br /> <br />This is considered in column 5 of Table 1 where estimates of the ~'maining <br /> <br />volume of debris are tabulated. <br /> <br />Thus, during a given storm Gulch A has <br /> <br />less water available to move the available debris than either of the other <br /> <br />two basins. As a result of thiB, Gulch A may remain as a persistent debris-flow <br /> <br />source for a longer period of time than either Gulch B or C. All three <br /> <br />basins easily contain suffic:lent debris to produce destructive flows for <br /> <br />a very long period of time (Figure 2). In contrast, much larger drainage <br /> <br />basins (several mi2 and larger) will usually have much larger A/K ratios, <br /> <br />- 10 - <br />