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<br />upstream of structures, acce~eration of flow around <br />obstructions, and ~verslon of flows (avulsions) are common <br />in the vicinity of developments. Hence, flow conditions are <br />very different within and down-fan from a development than <br />they are on an undeveloped fan. <br /> <br />The location of the development is a major factor, since <br />structures near the apex or within an entrenchment will be <br />severely damaged and will strongly influence flow paths and <br />damages down-fan. Dense developments will experience <br />hazards due to the high velocity, scour and inundation <br />effects of constricting the flood flows. structure and <br />street geometry can either mitigate or exacerbate flood <br />hazards within a development. streets designed to carry <br />flood flows without damage will, as shown by the locali=ed <br />model experiments (see Part II Section 5), effectively <br />protect structures and prevent landscape damages. <br />Conversely, a street pattarn which runs across the fan slope <br />may cause ponding, flow constriction, and unstable flow <br />paths. <br /> <br />4.5 Recommended Approach ~ Hazard Identification <br /> <br />, <br /> <br />In order to identify the presence and magnitude of flood <br />hazards on an alluvial fan, a detailed technical study of <br />the fan should be undertaken. This section reviews the <br />existing fIA hazard prediction methodology and then provides <br />a brief outline of the components that should constitute the <br />identification process. The development of a comprehensive, <br />detailed approach to hazard identification is beyond the <br />scope of this report. <br /> <br />The Federal Insurance Administration is presently applying a <br />method of hazard analysis on alluvial fans (Dawdy, undated) <br />that calculates depths and velocities with a one percent <br /> <br />52 <br /> <br />