Laserfiche WebLink
<br />): <br /> <br />· Flash Oooding- This is flooding that occurs in a short period of time. ' <br />It is most conunon when intense local rains fall on areas with steep <br />slopes or on built-up areas where impervious surfaces, gutters, and <br />stonn sewers speed up the flow of runoff. <br /> <br />· AlluVial fans-In mountainous' areas, high velocity flood flows pick up . <br />sediment as they move downhill. At the base of-the valley the slope <br />flattens out. The flood waters slow and spread out, as in sheet flow, <br />and drop the sediment over a wide fan-shaped area. <br /> <br />. <br /> <br />· Ice jams-Ice jam floods occur when warm weather and rain break up <br />frozen rivers. The broken ice floats downriver until it hits bottom at a <br />shallow spot or is blocked by an obstruction, such as a bridge. An ice <br />dam forms and blocks the channel, causing flooding upstream. <br /> <br />· Moveable bed streams-These are most conunon in the arid West, <br />where steep slopes and lack of vegetation result in a lot of erosion. <br />During a flood, a channel may be eroded more deeply or it may <br />become filled with sediment and move to a different location. <br /> <br />· Sewer backup-During heavy rains, stormwater may overload a <br />community's sanitary or stonn sewer system. If the water levels in the <br />receiving streams are high, the storm sewers can't drain. The water <br />will back up in the system, usually into basements and other low-lying <br />areas. . <br /> <br />Just as with riverine and coastal flooding, flood problems arise when development <br />does not take these special hazards into account. An additional concern is that <br />many flood hazard maps and flood loss reduction programs, such as building <br />codes, do not reflect the additional danger and damage potential that accompany <br />these other types of flooding. <br />To Find Out More .. .. For more information on these "special" hazards, <br />see Reducing Flood Losses in High Risk Flood Hazard Areas and CRS <br />Commentary Supplement for Special Hazards Credit (see Appendix B). <br /> <br />What Infunnation Do You Need? <br /> <br />::: <br /> <br />It is important to remember that every flood is different The next flood could be <br />worse than the floods you have already experienced. If you want protection from <br />flood damage, don't think only in terms of the last flood or the worst one you or <br />your neighbors remember. You will need to collect some information on the actual <br />risk of flooding in the future. <br /> <br />:j' <br />.' <br />, <br />, <br /> <br />The floodplain and flood levels <br /> <br />Most regulatory programs deal with the base flood. As discussed earlier, this is a <br />statistical concept that takes into account both the severity of a flood and the <br />likelihood of it occurring. Most of the nation's base floodplains have been mapped <br /> <br />. <br /> <br />.1 <br /> <br />10 <br />