d. Wave and Surge Qverwash . Overwash is a phenomenon which occurs during 

 periods of storm surge and severe wave action. Waves and overflowing water 

 erode the beach and transport and deposit this material shoreward of the 

 beach, or as an overwash fan on the bay side of low-lying barrier islands. 



e. Deflation . The removal of loose material from a beach by wind action 

 can be a significant cause of erosion. In many parts of the world, major nat- 

 ural dune fields exist well behind the active beach zone. These dunes can 

 represent a large volume of beach sediment. 



f. Longshore Sediment Transport . Sand is transported alongshore by waves 

 breaking at an angle to the shore. If the sediment carrying capacity of the 

 longshore current generated by these waves exceeds the quantity of sediment 

 naturally supplied to the beach, erosion of the beach results. 



g. Sorting of Beach Sediment . Sorting of beach sediment by wave action 

 results in the selective redistribution of sediment particles (sand, shell, 

 and shingle) along a beach profile according to size or hydraulic properties. 

 This mechanism is particularly important in designing beach nourishment 

 projects because the selective loss of finer material to the offshore region 

 and the retention of the coarse material in the surf zone require the place- 

 ment of additional fill in order to balance this loss. Best results are 

 usually achieved when the fill material is similar in grain-size distribution 

 to the native beach material. 



2. Man- Induced Causes . 



a. Land Subsidence from Removal of Subsurface Resources . The removal of 

 natural resources, such as gas, oil, coal, and groundwater underlying the 

 coastal zone, may cause subsidence of the beach. This has the same effect as 

 a sea level rise. 



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