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<br />6. SELECTION Of FLOOD PLAIN MANAGEM^NT TOOLS <br /> <br />6.1 Manaqement Tools Considered <br /> <br />field investigations, a literature search. and meetings with <br />local community officials have identified a number of <br />management tools which have been used. with varying degrees <br />of success. by communities on alluvial fans. One of the <br />major objectives of this study was to assess the <br />applicability and effectiveness of such tools and to make <br />recommendations as to the use of management measures. In <br />the following discussion each tool is described and typical <br />applications are cited. Later sections discuss measure <br />effectiveness and recommended usage. <br /> <br />Deb~is Basins QL Detention Dams <br /> <br />These measures can be placed on fans at the apex or across <br /> <br /> <br />stable channels and typically consist of a natural or <br /> <br /> <br />excavated basin confined by an earthen dam equipped with <br /> <br /> <br />outlet works and sp'llway. The purpose of most such <br /> <br /> <br />installations is to reduce the peak flood discharge of water <br /> <br /> <br />and sediment. Debris basins are designed to trap most <br /> <br /> <br />incoming sediment permanently. while detention dams trap <br /> <br /> <br />sediment and water during the flood peak and then release <br /> <br /> <br />both as the flood subsides. Both types of structures have <br /> <br /> <br />been used on several fans and aprons in the United States. <br /> <br />Levees and Channels <br /> <br />Levees can be used to confine or channelize flow anywhere on <br />a fan, but are typically used to convey flow all the way <br />from fan apex to toe. Design of levees and channels varies <br />widely, from the unarmored. uncompacted berms constructed on <br /> <br />65 <br />