subsequently buried with overwash sand which was carried up to 250 meters 

 beyond the bayward edge of the marshy Sediment deposited along the bay 

 shoreline was colonized by salt-marsh vegetation, and sand subsequently placed 

 on top of the salt marsh was colonized by dune vegetation. 



Nauset Spit-Eastham was extensively overwashed during the February 1978 

 northeaster. While 75 percent of the dune line was leveled and 32 percent of 

 the salt marsh was buried, only 1.7 hectares of new substrate was added along 

 the bay margin, resulting in barrier migration. Large-scale migration of 

 Nauset Spit-Eastham did not occur during this major storm because the barrier 

 was already widened prior to the storm due to the major overwash event during 

 the 1700' s. Reworking of these extensive washover deposits will eventually 

 lead to the formation of a new dune line in a position landward of prestorm 

 dunes. Overwash will have resulted in the migration of surface features along 

 Nauset Spit-Eastham. Because the basal peat layer will prevent future inlet 

 activity along the northeast section of Nauset Spit-Eastham, overwash will 

 eventually result in landward migration of this section of the spit system. 



On Old North Beach, core data revealed that washover sand had buried a 

 salt marsh approximately 200 years ago; peaty material was outcropping along 

 the ocean beach ir, 1978. Salt-marsh vegetation had colonized this washover 

 surface and survived long enough to form a peat layer before being buried by 

 overwash again. Thus, barrier rollover at this North Beach location and at 

 the location of the sinking of the Spavvow-Hauk in 1626 has been determined to 

 be less than 250 years. 



Overwash has been a major factor in the evolution of Old North Beach; 

 inlets have not affected this section of Nauset during the past 110 years. 

 While an average of 242 meters was lost to shoreline erosion during this 

 period, average barrier width decreased by only 90 meters since overwash 

 widened the barrier in many locations. Barrier width aldng 37 percent of 

 Old North Beach decreased because glacial deposits abutting the barrier have 

 made further migration impossible. Eventually the glacial highlands of Little 

 Pocket Island and Nauset Heights will be exposed to wave attack and the bar- 

 rier beach will be converted by erosion into a beach fronting a headland at 

 these locations. 



2. Vegetative Response to Overwash . 



The response of barrier-beach vegetation to overwash burial was studied 

 using U.S. Coast Survey maps and aerial photos as well as prestorm and post- 

 storm vegetation and elevation data. The location of dunes, salt marshes, 

 shrubs, and washovers was mapped along the spit system for periods from 1851 

 to 1978 to determine the rate of plant community development and morphologi- 

 cal changes along the barrier system. Vegetation and elevation data were 

 collected in 1977 and compared to data acquired after the February 1978 

 northeaster. The immediate response of major June and salt-marsh species to 

 overwash and the colonization of washovers were documented from these data. 



IXines play an important role in the stabilization of barrier beaches. 

 IXines, which act as barriers to wave attack during all but the most severe 

 storms, provide protection for back-barrier vegetation. Salt-marsh plants 

 become established in low-energy, intertidal regions of the barrier. Areas 

 that are subject to frequent overwash or swift bay-side currents do not 



215 



I 



