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<br />B. General ConsideratioIls <br /> <br />The recommendations contained in this chapter ::onsider the mechanical <br /> <br />properties and dynamics of debri" flows a. discussed in detail in Chapter <br /> <br />III. Summarizing this information, the fac tors wh ich must be cons idered <br /> <br />when recommending defenSE!S are:: <br /> <br />(1) Several distinct flow surges are possible and may <br /> <br />occur in rapid succe,ssion ill a drainage basin during <br /> <br />a single event. <br /> <br />(2) The flows may be several feet deep and often carry <br /> <br />large boulders on or near their tops. <br /> <br />(3) A debris-flow "urge will not necessarily maintain <br /> <br />a uniform velocity. <br /> <br />Instead, velocity can be <br /> <br />expected to fluctuate quickly in the channel or on <br /> <br />the debris fan in rE'sponse to water content changes, <br /> <br />terrain variabi.lity, and additional pressure from <br />behind. <br />(4) A debris flow "urge will _~~!c !,ecessarily. ~'pre,,-<!. <br />laterally like a flc'od, even on the unconfined surface <br /> <br />of a debris far.. <br /> <br />In,stead, it can remain confined <br /> <br />within a channE,l it builds as it flows across a fan, <br /> <br />thus maintainirg great flow depth. <br /> <br />-- 33 -- <br />