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<br /> <br />Storm drainagt is a signifirant probkm in mmry lnrge <br />urban areas, particularly if deveWpmmt has bfffl rapid <br />and not well planned. Drai11J:lge rystems must be designed <br />to !w.ndk infrequent, but potentially catastrophic, events. <br /> <br />Concrete-lined artificial channel caTT)'ing flood waters, <br />Baton lWuJ!t, Louisiana. <br /> <br /> <br />Hurricanes can result in flooding rif ~arious kinds, from <br />flash flooding and slow-rise riverine flooding due to heavy <br />precipitation, to coastal fWoding due to storm surge. <br /> <br />Quinebaug Rum, Putnam, Connecticut, 1955, following <br />Hurricane Diane. <br /> <br /> <br />HurrUalUs can cause severe damLlge dIU: to the combined <br />iff<<ts oj sn>eral agmts-high winds, increased wave ac- <br />tion, heavy precipitation, storm surge, and allILr types ~f <br />flooding. <br /> <br />Damage near CfuJrlestofl, South Carolina, following Hur- <br />ricane Hugo, September, 1989. <br /> <br />- <br />14 <br /> <br />highways, dams, and irrigation facilities all have changed the vegetative <br />cover, altered surface water patterns, changed the movement of sedi- <br />ments, and Imvered water tables. These changes have made water <br />movement during floods difficult to predict. <br /> <br />. Ice jams, which affect 35 states, cause a rapid rise of water both at the <br />point of the jam and upstream; when the jam breaks, sudden down- <br />stream flooding results. Because the waters are higher and their veloci- <br />ties greater, damages usually exceed those that would have occurred <br />without the jam, Additional damage can be caused by the force of the <br />ice, as it builds in volume and expands overbank during the jam and <br />then crashes downstream when the jam breaks. <br /> <br />Flooding from Surface Runoff <br /> <br />The runoff from heavy precipitation can overtax inadequate local drain. <br />age systems and result in flooding outside of normal floodplains. These kinds <br />of flooding problems generally intensify as areas become more urbanized. <br />Frozen ground and heavy accumulations of snow can exacerbate the problem. <br /> <br />Coastal Flooding and Erosion <br /> <br />Coastal flooding and erosion result from storm surge (the rise in the <br />water surface due to barometric pressure and the piling up of water as a <br />result of wind) and wave action (the combination of wave set-up and ,",,'ave <br />runup). The frequency and magnitude of flooding and erosion vary consider- <br />ably across the country. <br /> <br />. From 1899 to 1989 a total of 148 hurrUanes and 135 tropiaU sturms crossed <br />or passed adjacent to the U.S. mainland. <br /> <br />. Northeasters-extratropical storms accompanied by strong winds-cause <br />flooding along the north Atlantic coast. <br /> <br />. 7Sunamis are sea "...'aves generated by undersea earthquakes of over R6.5; <br />they are very long. period, are of low height at sea, and can travel over <br />500 mph. The entire Pacific coast of the United States, including <br />Alaska and Hawaii, is subject to tsunamis. <br /> <br />. Shoreline erosion occurs either when storm surge and wave action move <br />sediment offshore or when the alongshore flow of sediment is inter- <br />rupted by natural forces or human activities. Natural erosion may be <br />accelerated by partial or inadequate structural or nonstructural meas- <br />ures intended to protect short reaches of eroding shoreline-such as <br />beach nourishment, artificial dunes, breakwaters, seawalls, bulkheads, <br />revetments, groins, and jetties. <br /> <br /> <br /> <br />Number of Major Hurricanes Directly <br />Affecting the United States. 1899-1989 <br /> <br />Source: National Hurricane Center, ~ational \\"cather Service <br />