107. Driven by storm surges (Figure 15), overwash probably occurred 

 frequently in the study area before dune construction; however, it likely had 

 only a minor effect on the ocean and sound shorelines (Figures 52 and 53) . 

 Shoreline position changes do not seem to be related to island width for either 

 the ocean or sound shorelines, except near existing or recently closed inlets. 

 Away from inlets, the sound shoreline where the island was less than 900 m 

 wide retreated at an average rate of 0.6 m/year (Figure 53), which is greater 

 than the average retreat rate for island sections where the width was greater. 

 Accordingly, overwash probably did not significantly affect the sound shore- 

 line during the period from 1850 to 1980. If the effect were important, the 

 sound shoreline at narrow places on the island would have likely prograded as 

 sand moved from the beaches into the sound. 



108. Away from inlets, the retreat of the sound shoreline can be ac- 

 counted for mostly by sea level rise. At an average surface gradient of 1:100 

 near the sound shoreline, and a sea level rise of 0.004 m/year (Hicks 1981), 

 the sound shoreline retreat rate would be 0.4 m/year, or nearly the actual 

 rate measured. This rate will vary in the future as the sea level change 

 rate relative to the island varies. 



► OPEN N-S FACING COAST 

 • NEAR PAST OR PRESENT 

 INLET 



-a *- 



2000 2500 3000 



ISLAND WIDTH, M 



Figure 52. Ocean shoreline changes from about 1850 to 1980, Cape Henry 

 to Cape Hatteras, as a function of island width in 1980 (shoreline 

 changes are shown in Figure 28) 



98 



