the oceanfront, and material must be added to the back. -barrier margin. If 

 sand Is only lost along the oceanfront the barrier has simply eroded. If 

 sand is only added to the backshore without shoreline erosion, the barrier has 

 widened. Barrier migration occurs over long periods of time and is often the 

 result of continuous shoreline erosion with periodic back-barrier extension 

 resulting from inlet activity or overwash. 



Surficlal features, such as dunes, may move over the subaerial barrier 

 without the extension of the barrier beach as a whole toward the mainland. 

 Overwash and aeolian processes may transport sand across the dune line. On 

 northeast barriers, this sand is often deposited on salt-inarsh vegetation, 

 which does not recover from deep burial (greater than 33 centimeters). Dune 

 plants often colonize these deposits, resulting in landward displacement of the 

 dune line at the expense of salt-marsh vegetation. If new dunes form on the 

 site of previous salt marshes and no new substrate Is added to the bay 

 shoreline, the barrier as a whole has not migrated. 



There are three general mechanisms by which barrier beaches move landward: 

 (a) aeolian, (b) overwash, and (c) inlet processes. Along some sections of 

 the east and gull coasts, one of these processes may dominate. For instance, 

 large quantities of sand have been transported beyond the hack-barrier margin 

 by prevailing onshore winds at Padre Island, Texas (Malhewson, Clary, and Stin- 

 son, 1975). Overwash processes have been shown to dominate some small micro- 

 tidal barriers (Maurineyer, 1978). Sediment is carried across the barrier in 

 either small pulses with washovers, adding little sediment to the back barrier 

 or, on a larger scale, as long barrier sections are overw.ished, contributing 

 great volumes of sand to the bay shoreline. By far the most prevalent means 

 of barrier migration along the cast coast is by inlet-associated sand transport. 



At Nauset Spit, inlets historically have played a major role in landward 

 sediment transfers along all sectors and presently in many areas. N3uset Bay 

 is essentially filled with marsh Islands constructed on flood-tidal delta 

 deposits. Nauset Inlet continues periodically to migrate north and south, 

 introducing additional material to fill depressions while still maintaining an 

 inlet channel. The upper reaches of Pleasant Bay have also experienced much 

 sedimentation and, hence, shallowing by inlet activity. The earliest records 

 date to 1602 when explorers noted a series of inlets cut through the North 

 Beach barrier. This spit segment has undergone at least three different 

 series of inlet formation with subsequent inlet migration downdrift. In this 

 process of cyclic inlet breaching and spit regeneration, the entire barrier 

 structure has been effectively displaced landward. Only at Chatham Harbor has 

 the barrier rebuilt in the same general location during the last cycle (1860's 

 to present) since a particular hydraulic area of the channel roust be maintained 

 to accommodate the tidal flow within Pleasant Bny. North Beach may now be in 

 a position that the historic barrier spit fronting the glacial headlands of 

 Chatham will not reform, resulting in future cliff erosion by direct ocean 

 wave attack. 



During this study of barrier beach processes along Nauset Spit, the impor- 

 tance of inlet dynamics and overwash in barrier migration became evident. 

 Barrier migration was studied using shallow cores, early maps, aerial photog- 

 raphy, and individual storm data. Core data showed that overwash previously 

 occurred along some sections of Nauset. On Nauset Spit-Easthara, a salt marsh 

 existed behind barrier dunes approximately 815 years B.P. This marsh was 



214 



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