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<br />accomplished on nea~ly all pa~ts of a fan which <br /> <br /> <br />have no st~ble ent~enchments o~ st~ong <br /> <br /> <br />mo~phologic bias. <br /> <br />. High velocities cause seve~e e~osion and/o~ <br /> <br /> <br />ove~topping of levees. dikes, channels. and <br /> <br /> <br />st~eets whe~eve~ ~apid changes in flow <br /> <br /> <br />di~ection occu~. Flow conveyance st~uctu~es <br /> <br /> <br />must be smooth and continuous to avoid such <br /> <br /> <br />p~oblems. <br /> <br />. Deb~is and viscous sediment/wate~ miKtu~es <br />moving at high speed, as f~equently occu~ on <br />fans in the Los Angeles basin and elsewhe~e. <br />may seve~ely d~mage houses ~aised on piles. <br />walls. levees. and local dikes which would <br />withstand the clea~ wate~ flows typical of <br />~ive~ine.flooding. <br /> <br />Failu~e to conside~ these effects du~ing design and <br />const~uction of management tools may ~esult in cat~st~ophic <br />failu~e and seve~e flood damages. Cases whe~e such failu~e <br />has occu~~ed include Rancho Mi~age and Palm Dese~t. <br />Califo~nia and Bullhead City. A~izona. <br /> <br />Effect ~ Hvd~aulic ~ <br />The th~ee definable hyd~aulic zones discussed in section 4.2 <br />eKhibit substantially diffe~ent flood behavio~ and haza~ds. <br />~equi~ing diffe~ent app~oaches to flood management. <br /> <br />. The chilnnelized 1...l.2..!o! zone eKhibits ve~y high <br />velocities with la~ge scou~ potential ~nd la~ge <br />sediment loads. Management tools that a~e <br />designed to cont~ol the flow (channels o~ <br />levees) must be heavily a~mo~ed. Local flow <br />cont~ols such as dikes and dep~essed st~eets <br /> <br />89 <br />