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6. INTERACTION WITH NATURAL FEATURES AND CONSTRUCTED WORKS 



6 . 1 INTRODUCTION 



Assuming that sea level will rise a significant amount over the next 

 century, and that shorelines will generally respond in some manner, the 

 question arises as to by what means can (or will) this response be modified 

 or prevented. Natural features such as shoals, headlands, inlets and even 

 barrier islands themselves will cause the neighboring shorelines to respond 

 in a manner different from that of the typical "open" coast. Man-made 

 engineering works, e.g., breakwaters, jetties, and beach fills, by their 

 very purpose alter shoreline response from that of nature, and so can 

 modify shoreline response to sea level rise. Alternatively, the design, 

 construction, and cost of coastal projects is highly dependent on local 

 water depth. Relative sea level rise must therefore be addressed for a 

 project having a long design life. 



On a sandy coast, sea level rise generally invokes shoreline response 

 by two mechanisms. First is simply the retreat due to flooding or 

 inundation, which is often small because natural beach profiles are usually 

 concave upwards in shape. However, the rise in sea level builds a large 

 potential for additional erosion and shoreline retreat induced by wave 

 action, which can be quite severe. The only means of preventing shoreline 

 retreat due to inundation is by constructing dikes and seawalls. All other 

 features which modify shoreline response, both natural and man-made, do so 

 by altering or reducing the wave climate and have little effect on the 

 inundation component. These features/structures are now discussed 

 individually . 



6.2 NATURAL FEATURES 



Barrier islands - are the elongated natural islands composed of sandy 

 material, which front a substantial portion of the mainlands of the world. 

 These islands block out the wave activity to which the mainland shoreline 

 would otherwise be subjected, essentially acting like large breakwaters. 

 Although the mainland shorelines are still vulnerable to flooding due to 

 sea level rise and wind-waves generated locally in the bays, barrier 



