Salt-marsh area also decreased between 1938 and 1952 (11 percent). Sev- 

 eral new marshes developed as others were buried by washovers or eroded along 

 the bay side. Thirty-eight percent of the 1938 salt-tnarsh area was lost by 

 1952; 55 percent of the salt marsh present in 1952 had developed over 14 

 years. 



Between 1952 and 1978, the length of North Beach increased slowly at a 

 rate of 54 meters per year; 1500 meters was added at the terminus. Luring 

 this period, spit recurves formed opposite the embayzaent between Chatham Light 

 and Morris Island and across from the breach between Karris Island and the 

 northern end of Monomoy Island (Fig. 3)= By 1978 the spit was approximately 

 1600 meters short of its maximum length in 1851. 



An average of 5.5 meters per year was lost from New North Beach shoreline 

 between 1952 and 1978. In one area opposite Chatham Light, the bay shoreline 

 of 1952 was seaward of the 1978 ocean shoreline, indicating migration exceed- 

 ing the 180-meter barrier width in 26 years. Overwash had widened the barrier 

 in this very narrow region without developing an inlet. Average barrier width 

 of New North Beach was reduced to 279 meters despite the development of a 

 broad dune field at the southern end of the spit. A total of 83.8 hectares of 

 supratidal barrier was lost along the ocean shoreline. Erosion also continued 

 along the bay shoreline where 13.5 hectares was eroded (Table 51). Overwash 

 was locally important in the maintenance of barrier width; 15.5 hectares was 

 added to the back, barrier. In one area, however, across from Chatham Ught, 

 the barrier was only 74 meters wide in 1978. If erosion rates of more than 

 5 meters per year continue, this area would be entirely eroded in 15 years 

 unless overwash significantly builds new bay-shore substrate . 



Although dune environment increased by 50 percent between 1952 and 1978, 

 approximately one-half of the dunes present in 1952 had been leveled by shore- 

 line erosion (44 percent of the dunes lost) and overwash (47 percent). few 

 dunes developed at the spit terminus (54 percent of the new dunes) and on 

 washovers (33 percent). 



Although the total salt-marsh area decreased by only 2 percent bstvs-sen 

 1952 and 1978, much of the marsh was newly created; only 23 percent of the 

 1952 marsh was still present In 1978. The marsh had been destroyed by wash- 

 overs (69 percent) and by dunes that had developed on washovers (31 percent). 

 New marsh developed at the spit terminus (25 percent of new taarsh) , on wash- 

 overs (34 percent), along the bay shoreline (27 percent), and in areas that 

 had been mapped earlier as dunes (14 percent). 



Since it began to develop in the 18b0's, New North Beach has been subject 

 to very rapid shoreline changes (Fig. 107). Between 1938 and 1978, 230 casters 

 and 575.8 hectares of barrier envi 'onatent was lost along the ocean shoreline. 

 New North Beach also decreased in width from the bay shoreline. U'hile the 

 back-barrier surface increased by 21.2 hectares from overwash and tidal 

 sedimentation, tidal currents eroded 66.4 hectares of barrier along the bay 

 shoreline. The calculated ocean shoreline erosion rate of 5.0 meters per year 

 between 1938 and 1978 correlates well with the 5.9 meters per year obtained by 

 Gatto (1979). 



As the spit Increased in length, it decreased in width. The ratio of 

 width to length was calculated for New North Beach for each set of maps 

 (Table 53). Width-to-length ratio may be of value to predict susceptibility 



183 



