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<br /> <br /> <br />ALLUVIAL FAN FLOOD MANAGEMENT <br />TOOLS <br />(Based on Size and Density of Planned <br />Development) <br /> <br />Whole Fan Protection <br /> <br />Levees <br /> <br />Channels <br /> <br />Detention basins <br /> <br />Debris basinslfences/deflectors/dams <br /> <br />Design Considerations: Whole-fan protection includes large- <br />scale structural measures appropriate for use on extensively- <br />developed fans, and which are most cost-effective in high- <br />density s~uations. Structures must be designed to intercept <br />upstream watershed flow and debris at the apex and to <br />transport water and sediment around the entire urbanized fan. <br />Structures must be designed to withstand scour, erosion, <br />sediment deposition, hydrostatic forces, impact and hydrody- <br />namicforces, and high flow veloc~ies. Continual maintenance <br />is essential for optimal operation, and can be costly. These <br />structures are most often funded through federal and state <br />sources, but can also be financed through special regional <br />districts, local governments, or developers. <br /> <br /> <br />Figure 14. . <br />This concrete chanMI wss designlHi to carry floodwat.r downslope In <br />Palm Desert, Califomla.- <br /> <br />Subdivision or Localized Protecllon <br /> <br />Drop structures to reduce flow veloc~y <br /> <br />Debris fences <br /> <br />Local dikes, channels <br /> <br />Site plans to convey flow <br /> <br />Street design/alignment to convey flow <br /> <br />Elevation on armored fill <br /> <br />Design Considerations: These are smaller-scale measures <br />that can be used throughout moderate-dens~y fans to safely <br />trap debris, and to route water and sediment around or through <br />individual residential developments. Protection elements must <br />prevent formation of new flow paths and/or the relocation of <br />existing paths; flood control structures must resist high veloci- <br />ties, erosion, depos~ion, hydrodynamic and hydrostaticforces. <br />The most effective strategy includes a combination of ele- <br />ments; the entire protection plan must be coordinated with <br />other similarly-scaled efforts to avoid adverse impacts to <br />adjacent property. These measures can be financed privately <br />by developers. <br /> <br /> <br />Flgu,..15. <br />Shown h.,.. Is the channelization of Flamingo Wash adjacent to nsw <br />construct/on nsar Las VBg8.S, N.....da. Gabion. (rock.fiIJlHl basksts .n- <br />e/osed with wi,. mesh) help stabilize the chanfNl side./oplJs. Walls <br />provid. som. addltiona' flood protscUon. <br /> <br />9 <br />