several northeasters. Washover fans or flats served as temporary reservoirs 

 for sand returned to the beach by prevailing offshore winds. Wind deflation 

 was minimized only in regions where the barrier was narrow or low enough to 

 deposit overwash in the bay or near the water table. These results indicated 

 that small-scale overwashes do not play a significant role in the landward 

 migration of Assateague Island. Sediment from minor overwashes is rapidly 

 transported offshore by winds. Inlets are regarded as the primary me2.ns of 

 barrier migration within a geologic time frame (Fisher and Stauble, 1977; 

 Leatherman, Williams, and Fisher, 1977). 



Armon (1975, 1979) showed that more than 90 percent of landward sediment 

 transfers on the Malpeque barrier system were associated with the presence of 

 inlets. Overwash and aeolian processes were important in the development of 

 dunes. Rosen (1979), who also worked in the Canadian barriers of the Gulf of 

 St. Lawrence, found that aeolian reworking of sand on washovers is an impor- 

 tant factor in dune building. Therefore, the vertical accretion of barrier 

 islands is largely governed by the interaction of overwash-aeolian processes 

 and plant communities. This result correlates with Leatherman's (1979b) 

 results at Assateague Island. 



2. Overwash Hydraulics . 



a. Introduction . During storms, the convex beach profile is planed off 

 by waves, while a large storm bar is constructed a short distance offshore. 

 At high tide, swash may impinge directly on the seaward face of barrier dunes. 

 Low profile areas, created by blowouts or vehicles, allow swash penetration 

 as overwash through the dune line. Overwash is defined as the transport of 

 seawater and associated sediment or drift from the beach face to the back 

 barrier. As overwash surges cross the dune line, additional sediment is 

 eroded from the throat section, transported landward, and deposited in a fan 

 shape to the lee of the dunes (Fig. 4). The extent of the erosional zone 

 depends on flow conditions, which are a function of storm intensity. During a 

 severe coastal storm, large sections of the barrier dune may be overtopped and 

 flattened, forming extens /e washover flats. 



The throat is that section of a washover through the dune line. Constric- 

 tion of waterflow in the throat often results in erosion. Once the overwash 

 surges traverse this area, the flow is allowed to diverge due to the lack of 

 horizontal constraints and the typical fanlike feature is created on the back 

 barrier. Surge velocities are reduced due to flow divergence, frictional 

 effects, and percolation losses, and the flow is generally depositional in 

 nature. During overwash, the bay waters are superelevated with the storm 

 tide. Where overwash surges pass into pondad water, velocities decrease 

 quickly and sand is deposited rapidly, often resulting in steeply dipping 

 delta foreset beds at the fan terminus. 



b. Methodolog y . During the winter, weather was monitored continuously 

 to predict possible coastal storms. Storm path and morphology of large north- 

 easters capable of producing overwash at existing dune breaches on Nauset Spit 

 were closely observed. Storms were usually detected early enough for the 

 field team to reach the study site, set up the necessary instrumentation, and 

 conduct a preoverwash survey. 



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