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islands are the paramount safeguard against realization of the full 

 erosional potential of sea level rise in the back-bay region. This 

 potential is especially strong because the sediments found here are often 

 fine sands, silts, clay and peat, all highly erodible. 



If sea level rise causes local barrier islands to deteriorate, breach 

 more frequently, and "drown in place" rather than migrate landward, 

 progressively more wave energy will penetrate through the chain and attack 

 the mainland shoreline. This can result in enlargement of the bay area as 

 the mainland erodes. An example is the Isles Dernieres on the coast of 

 Louisiana, see Penland, et al . (1985). As shown in Fig. 6.1, since 1853 

 the large barrier has deteriorated drastically to become a series of five 

 small islands, which have retreated about 2 km in 125 yr. Most of this is 

 due to inundation and erosion accompanying the rapid subsidence of the 

 delta region. Concurrently, Lake Pelto has been greatly enlarged by 

 erosion of both the isles and the mainland. As the isles continue to 

 disappear, erosion of the mainland should accelerate. 



Shoals - are large deposits of sediment, usually associated with 

 relict barrier islands, inlets, and large headlands. They serve to 

 naturally limit the wave energy that impacts a shoreline, as a result of 

 dissipation due to bottom friction and breaking, as well as partial 

 reflection. As sea level rises, shoals become less effective unless their 

 natural response is to grow, as is the case at inlets as described 

 subsequently. Such growth of course requires sediment and may demand it 

 from neighboring shorelines or inlets. An example of the effects of 

 offshore shoals on the neighboring shoreline is Cape Canaveral, Florida, 

 shown in Fig. 5.2. This cape has an extensive system of offshore and 

 shore -connected shoals, which generally protect the cape from storm wave 

 activity out of the northeast. Little protection is afforded from the 

 southeast. The regional direction of net longshore drift is from north to 

 south, and the offshore shoals A, B, C and the Hetzel Shoal have afforded 

 enough protection for the Chester Shoal and False Cape to form utilizing 

 this supply of sediment. The entire shoal system is responsible for the 

 formation and protection of Cape Canaveral and Southeast Shoal. Farther to 

 the south the shoreline assumes a crenulate shape as is common for such 

 features. Field and Duane (1974) report that since 1878 Chester and 



