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<br /> <br />INTRODUCTION <br /> <br />15 <br /> <br />.., <br /> <br />FIGURE 1-2 Example ofa map that can be used to indicate areas requiring various fonns ofaltention in flood risk <br />assessment. The areas with solid shading are recognizable channels; the darker ones have stable fonns and <br />positions; the lighler shaded ones have the capacity to change fonn or position. A is an old fan surface that has <br />been entrenched and does nol receive runoff or debris flows from thc mountain source area. and is nOI being <br />undennined. B is a surface that is entrenched (but stands at an elevation below that of A), and will not be flooded <br />or invaded by channels, which can become subject to these hazards if the current channel becomes blocked by a <br />debris flow deposit. C and Dare respeclively bouldery lobcs and Icvees indicating deposition by debris flows within <br />and along channels. E denotes distributary channels that show no evidence of major scour, fill. migration. or <br />avulsion during recenl large floods and can convey all or most of a 1 pcrcent flood, as indicated by reasonably <br />applied flood conveyance equations. Areas indicated with F are subject to sheetflooding. G is a channel with signs <br />of recent migration and for which future behavior is highly uncertain. H is a surface which is subject 10 overbank <br />flooding, channel shifting, or invasion from a distributary channel that might erupt from G, and hence is the <br />surface subject 10 alluvial fan flooding, as defined in this report. Further details of these processes and fonns are <br />given in Chapters 2 and J. <br /> <br />