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<br />earthquakes, and other natural forces that can trigger ex- <br />cessive erosion, mud slides, and flash flooding Great <br />Lakes coastal areas are subject to erosion and severe win- <br />ter storms. The Atlantic and Gulf Coasts are consistently <br />exposed to the forces of hurricanes, lesser tropical storms, <br />and northeasters. Each of these coastal areas suffers signif- <br />icant flooding, but it is the latter that has received the <br />greatest amount of damage <br />Bala1Ue of Coastal System. Most of the Atlantic and <br />Gulf Coasts are made up of a succession of low-lying bar- <br />rier islands, beaches, sand dunes, and bluffs. This collec- <br />tion of physiographic elements constitutes a fragile eco- <br />system that serves an important function in maintaining <br />the natural environment <br />A dynamic balance of natural elements occurs as the <br />movement of sand by wind, waves, and ocean currents <br />maintains the beach and dune system Dunes serve to <br />catch and hold sand, thus keeping a constant supply to <br />replenish the natural erosion of beach sand This coastal <br />system helps buffer the force of storm tides and surges. <br />Wetlands, which are often an added element in the coastal <br />system, provide flood water storage and protect again..<;t <br />storm-induced erosion. <br />Physiographic charaoeristics vary along the length of <br />the coast, and influence the type and extent of flooding. <br />Beaches may be wide and flat, with low dunes, or they <br />may be of medium-to-narrow width, with higher dunes <br />and bluffs back from the ,",'atet The coast may be terraced, <br />with height gradually increasing as the distance from the <br />water increa.';;;es. Or there mav be a barrier dune or sand <br />bar as a natural levee betwe~n water and land These con- <br />figurations will influence flooding by providing variable <br />degrees of buffering. <br /> <br />The Built Environment <br /> <br />As noted in the previous chapter, development along <br />coasts and rivers is the result of a logical evolution, with <br />human settlements benefiting both socially and economi- <br />cally from the natural system The majority of this devel- <br />opment occurs in urban area~ but is also apparent at the <br />urban fringe, in small towns, and in rural areas Develop- <br />ment ranges from the single isolated building to the <br />multi-building complex, and includes residential, com- <br />mercial, and industrial building type& <br />However, this pattern has also led to a conflict be- <br />t\:veen natural and social systems. The need and desire for <br />direct access to water has resulted in human occupancy <br />oflow-lying areas, and this has put a large proportion of <br />the built environment in flood-prone areas. The flood- <br />plain is transformed into a flood hazard area, and destruc- <br />tion of the human habitat becomes commonplace <br /> <br /> <br />~~.- <br />~ <br /> <br />Low Dunes and Flat Beach <br /> <br /> <br />Low Coastal Bluff and Narrow Beach <br /> <br /> <br />I <br />High Dune and Wide, Sloping Beach <br /> <br />h~~ <br /> <br />, '''L___~~~~~", <br />-, <br /> <br /> <br />i:,Wdli,'II!,: <br /> <br />Terraced Coast <br /> <br />Variations in coastal to- <br />pography can influence <br />the extent of flooding he- <br />cause of their variable re- <br />sistance to storm surges <br />and tidal waves. <br /> <br />15 <br />