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<br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />'. <br />. <br />. <br /> <br />I: <br />. <br />. <br />. <br />. <br />. <br /> <br />12 <br /> <br />02/23/00 <br /> <br />Table 1. Methods for defining the 100-year flood within areas defined in Stage 2. <br /> <br /> <br />Refer to Guidelines for Risk and <br />Uncerlainry Analysis in Waler <br />Resources Planning (V.S, Army Corps <br />of Engineers, 1992), <br /> <br />FAN Program flooding in rectangular channel; critical <br />depth, erosion of rectangular channel <br />banks until the change in width per the <br />change in depth equals -200: the <br />probability density function of a <br />discharge occurring at the apex is log- <br />Pearson Type 1l1; the frequency of flood <br />events for various recurrence intervals, <br />i,e., 2-year through 500-year, can be <br />adequately defmed; equal probability <br />along contour arcs (random flow paths); <br />(also provides for multiple channels at <br />normal depth, assuming total width is <br />3,8 times the single-channel width) <br /> <br />Risk-Based <br />Analysis <br /> <br />Sheetflow broad, unconfmed, shallow flooding <br /> <br />Hydraulic <br />Analytical <br />Methods <br /> <br />stable flow path, uncertainty is to a <br />degree that may be disregarded <br /> <br />Geomorphic Data, <br /> <br />Post-Flood <br />Hazard <br />Verification, and <br />Historical <br />Information <br /> <br />Composite as identified in the sections referring to <br />Methods the methods being applied <br /> <br />.- <br /> <br />relies primarily on qualitative <br />information, post-flood verification, <br />historical data, and interpretive studies <br /> <br />fluvial (as opposed to <br />debris flow) formed <br />fan, unstable flow <br />paths <br /> <br />not for use in areas of <br />undulating terrain <br /> <br />not for use with <br />active alluvial fan <br />flooding <br /> <br />approximate method <br /> <br />must integrate <br />multiple methods into <br />one result <br /> <br />highly active conical <br />fans <br /> <br />shallow flooding across <br />uniformly sloping <br />surfaces <br /> <br />entrenched stable <br />channel networks, <br />constructed channels, <br />urbanized areas <br /> <br />alluvial fans with little or <br />no urbanization <br /> <br />floodprone areas that <br />contain unique physical <br />features in some <br />locations or have areas <br />varying in levels of <br />erosion and migration <br />activity <br /> <br />9 <br /> <br />2 and 8 <br /> <br />3 and 4 <br /> <br />5,6, and 7 <br />