Overwash also occurred to the north and south of site 3. O.ly 5 meters of ) 



dune to the north and 15 meters of dune to the south remained after the storm, '; 



leaving site 3, once the only washover in the area, stranded among the wash- | 



over flats. Washover sediments from the north and south channels coalesced on j 



the marsh at site 3. } 



The centerltne transect through site 3 throat and fan (15S) extended west 

 and was surveyed before and immediately after the February storm (Fig. 19). j 



Sand deposition occurred as far as 135 meters west of the 1977 benn crest. 

 The greatest recorded deposition on Nauset Spit-Eastham resulting from the \ 



February storm was recorded at site 3, where 1.65 meters of sediment was j 



deposited on the old road bed at 160W. The beach profile was planed off and 

 the storm berm was displaced 15 meters Landward of its prestorn position. The 

 total amount of overwash deposition was 400 cubic meters per running meter of } 



dune overtopping or breach. 



i 

 (a) Site 3 Throat. Site 3 throat experienced less extensive J 



erosion and deposition during the February storm than did site 1 throat, being 

 a major overwash channel. Three-dimensional plots of site 3 were made from ; 



elevation data collected at the 5- by 5-raeter grid in August 1977 and June 

 1978 (Fig. 20). The backdune area (40W to 50W) was steeply scarped (1 meter) . 



in 1977 at the edge of the road, and overwash surges eroded the outer 1 meter ' 



of the area. In vegetated areas, such as at site 3 throat, the greatest ! 



deposition occurred toward the back, of the dune line; little deposition 

 occurred near the new benn crest. From the 77 elevation points surveyed for 

 the 5- by 5-raeter grid, mean elevations relative to a USGS bench mark w*re 

 calculated for 1977 (1.78 meters) and 1973 (1.94 tseters) . A comparison of j 



elevation statistics for 1977 (a = 0.44 meter; range = 2.10 meters) and 1978 i 



(a =0.15 meter; range = 0.69 meter) shows the flattening effect of overwash I 



on dunes. ) 



(b) Site 3 Fan. Site 3 fan was not eroded during the February 



storm, but was entirely buried by washover sand. Three-dimensional plots of ■ j 



elevation data taken in August 1977 and June 1978 show that the road and the J 



salt marsh were subject to deep burial (Fig. 21). The greatest deposition i 

 occurred closest to the sand road. From the 56 elevation stations surveyed 



for the 5- by 5-meter grid, the mean elevation and range were calculated for ;. 



1977 (0.15 meter; range - 0.28 meter) and 1978 (0.77 meter; range = 0.67 f 



meter). The standard deviations (1977, o = 0.08 meter; 1978, o ■ 0.19 meter) ; 



show the increase in slope in the marsh caused by overwash burial. j 



« 



4. Aeolian Reworking . . 



a. Introduction. Although a considerable amount of sand was deposited by j 



overwash on Nauset Spit-Easthara, much of this sediment has been redistributed 

 during interstorm periods. Tidal currents have reworked sand along fan mar- 

 gins, but wind has been the principal means of redistributing the sediment. . 

 Prevailing northwest and southwest offshore winds during the winter often 

 exceed i0 knots per hour and frequently average 10 to 15 knots per hour. 

 Since this wind field is generated by Canadian high-pressure cells, strong J 

 winds are accompanied by clear weather, resulting in maximum transport because 

 the sand is dry. 



47 1 



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