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<br />Local levees and st~eet conveyance can be used <br /> <br /> <br />effectively only if the eXlsting development <br /> <br /> <br />patte~n allows the use of st~eets as ch~nnels. <br /> <br />. When an area of a fan has been fullY developed <br />~ high densities without ~ega~d fo~ flood <br />management, only whole-fan management tools <br />will provide adequate p~otection fo~ the <br />existing st~uctu~es. In fact, piecemeal <br />application of local management tools such as <br />dikes and elevation on fill will result in <br />greate~ damages fo~ some st~uctu~es, while <br />other st~uctures a~e p~otected. This is <br />because dikes and a~mo~ed fill dive~t flows <br />~ather then containing and cont~olling the <br />flood. <br /> <br />, <br /> <br />It is clea~ f~om the. above discussions that flooding on <br />spa~sely developed fans can be managed more easily and <br />cheaply than flooding on developed fans, unless such <br />development has followed a flood man~gement plan. The <br />numbe~ of available options dec~eases ~apidly with existing <br />development density. This alone is sufficient justification <br />for the establishment of a comp~ehensive flood management <br />plan (maste~ plan) before significant development occu~s. <br /> <br />One additional management optiDn has not been included in <br />Figure 4.3 because it does not p~ovide flood p~otection fo~ <br />existing st~uctu~es on a fan. This option, which can be <br />thought of as a "minimum expenditu~e" plan, p~ovides only <br />fo~ flood protection of new st~uctu~es USing elevation on <br />piles. This allows continued development of an a~ea without <br />changing the existing hyd~aulic conditions (e.g., a~ea open <br />to flood flows, slope, etc.) o~ inc~easing damages to <br />existing structu~es. All management costs, which a~e small, <br />a~e bo~ne by develope~s and homeowne~s. <br /> <br />92 <br />