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<br />v = 1.49 (AlP)2/3 Sl/2 <br />n <br /> <br />where: V = Average flow velocity (feet <br />per second) <br /> <br />A = Cross-sectional flow area <br />(feet)2 <br /> <br />P = Wetted perimeter of A (feet) <br /> <br />S = Bed slope (feet/feet) (use <br />average ground surface <br />slope within a reach from ap- <br />proximately one-half mile <br />upstream to approximately <br />one-half mile downstream) <br /> <br />n = Manning's channel <br />roughness coefficient <br /> <br />Frequency-Frequency of flooding is a major <br />consideration in the evaluation of potential in- <br />stallation sites. Frequency of flooding is the <br />probability (in percent) that a random flood event <br />will equal or exceed a specified magnitude in <br />a given time period. Manufactured homes sited <br />at. lower elevations near a flooding source will <br />likely have a higher frequency of flooding than <br />those located on higher ground away from the <br />. flooding source. Flood frequency information is <br /> <br />included in FIS reports and other technical <br />floodplain studies. Frequency of flooding can <br />aiso be statistically determined using historical <br />records of flooding at the location under <br />consideration. <br />Rate of Rise-The rate of rise 'of a flood is an <br />expression of how rapidly water depth increases <br />during a flooding event. This factor is important <br />in evaluating buoyancy hazards and in- <br />vestigating the feasibility of an evacuation plan. <br />The rate of rise of f1ood- waters can be derived <br />from a stream flow hydrograph that relates <br />flooding depth to time for the area under con- <br />sideration. Information required to determine the <br />rate of rise may also be obtained from existing <br />hydrologic studies, on-site investigations, <br />historical records, and local civil defense offices. <br />Duration-The duration of flood inundation, <br />which is a function of the rate of rise and fall <br />of water, has several important influences on <br />a manufactured home installation. Duration in- <br />fluences the saturation of soils and building <br />materials, the amount of seepage, and the <br />length of time that a manufactured home might <br />be inaccessible. The various fioodplain technical <br />studies and historical records are sources of in- <br />formation concerning duration of flooding. <br />The following tables provide sources of <br />various types of information and assistance. <br /> <br /> <br />FLOOD PLAIN <br />AGENCIES <br />. Federal Emergency . . . . . <br />Management Agency <br />. U.S. Army Corps of . . . . . . .. . <br />Engineers <br />. U.S. Soil Conservation . . ,. . . <br />Service <br />. Department of Housing . . <br />and Urban Development <br />. National Oceanic and . <br />AtmospheriC Adminstration . <br />. U.S. Geological Survey . <br />. Federal Highway . . . <br />Administration <br />. State Floodplain Management . . . . . . <br />Coordinating Agency <br />. Regional Authorities . . . . . . . <br />. local Government . . . <br />Planning Agencies <br /> 86 <br />