Table 42. Erosion rates along the Nauset Spit system using serial 

 map overlays. 



Area 



1851, 

 1868-86 



1856-1938 



1886-1933 



1938-52 



1952-73 



1851, 1836, 

 1868-1978 





(o/yr) 



(m/yr) 



(ra/yr) 



(o/yr) 



(o/yr) 







a/yr) 



Nausec Spit- 

 Sastham 





0.7 





3.3 



0.5 





0.9 



Old North 

 Beach 



0.7 





1.7 



2.7 



1.3 





1.5 



New North 

 Beach 



22.8 







6.2 



5.5 





5.8 



most rapid rate of erosion occurred between 1933 and 1952 when an average of 

 3.3 meters of beach per year was lost. Between 1952 and 1978, the rate slowed 

 to 0.5 meter per year, although in some areas as much as 10 meters of shore- 

 line erosion occurred during the February 1978 storm. The 40-year erosion 

 rate of 1.2 meters per year correlated well with 1.3 meters per year obtained 

 by Zeigler, et al. (1964), and Gatto (1979) (Table 40). The erosion rate 

 obtained by Marindin (1889) from field surveys between 1856 and 1886 (0.1 

 meter per year) reflects a period when Nauset Spit-Eastham experienced little 

 erosion. These data agree with the relatively low rats of erosion obtained 

 in this study (0.7 meter per year) using measurements taken from both the 

 1856 maps and the 1938 photos. 



The average width of Nauset Spit-Eastham has consistently decreased since 

 1868 (Table 43). Comparing only that part of the spit north of the 1978 

 inlet, overall barrier width has decreased from 430 meters in 1"68 to 293 

 meters in 1978. Shoreline erosion removed 110 meters from the oceanfront 

 which accounts for most of the narrowing of the spit. During the 122-year 

 period, 11.9 hectares was lost f rom the bay shoreline of the barrier, but most 

 of this loss occurred in the southern 2.1 kiloseters of the spit where tidal 

 currents eroded marsh and sandflat environments (Table 44). Additions to the 

 back of the barrier by rhizome outgrowth onto tidal sedimentation and by over- 

 wash totaled 18.4 hectares. This new substrate was deposited locally in the 

 southern 2.1 kilometers of the spit and these areas have been destroyed as the 

 inlet migrated northward. 



The width of Nauset Spit-Easthsm presumably exceeds the critical minimum 

 barrier width at which washover deposits can add significant amounts of sub- 

 strate to the back side of the barrier. In 1978 a major overwash occurred 

 along Nauset Spit-Eastham. Although 26.9 hectares of washover was mapped 

 after the storm (Table 45), only 1.7 hectares of new substrate was added to 

 the bay side of the barrier; 25.2 hectares of washover was deposited on 

 previous dune and salt-marsh environments. 



Nauset Spit-Eastham is composed of four primary environments: dune, salt 

 marsh, washover, and sandy shoreline. The area of each environment was calcu- 

 lated for each map (Table 45; Fig. 102). The total supratidal area of Nauset 

 Spit-Eastham has decreased by 48 percent in 122 years — from 152.8 hectares in 

 1856 to 78.9 hectares in 1978. All the environments except washovers have 

 decreased dramatically in size. 



170 



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