(Apps. C and D) . During those two summers the shoreline at profile line 

 8 accreted an average of 26 meters and the above MSL volume increased an 

 average of 72 cubic meters per meter. Winter erosion more than equalled 

 these amounts. However, profile lines 12, 15, 19, and 20, immediately 

 to the east of groins, underwent erosion during the summer months in 

 which they were surveyed. Profile lines 13, 16, and 17 on the west side 

 of groins (Fig. 15) , underwent significant accretion during the same 

 summers. In planning the location and timing of beach nourishment, these 

 seasonal reversals in transport direction must also be considered. 



VII. SUMMARY 



From 1962 to 1973, 1,291 beach profile surveys were collected on 20 

 profile lines from the dune to wading depth at Westhampton Beach, New 

 York. Frequency of surveys ranged from weekly to quarterly (Fig. 7). 

 During the study, prestorm and poststorm surveys were made which docu- 

 mented changes resulting from 2 7 moderate northeaster storms and 1 hurri- 

 cane (Table 2) . 



The largest changes measured (in order of decreasing severity) were 

 during the storms of March 1973, February 1969, February 1972, and Sep- 

 tember 1967 (Table 2; Fig. 11). The seasonal change in beach width for 

 11 profile lines averaged 30 meters; the seasonal sand volume change 

 above MSL averaged 56 cubic meters per meter (Apps. C and D) . 



Beach change rates are separated into three categories: east of the 

 groin field (profile lines 1 to 4) , within the groin field (profile lines 

 5 to 9), and west of the groin field (profile lines 10 and 11). During 

 the 11-year study period, profile lines 1 to 4 accreted at a rate of 1.10 

 meters per year MSL shoreline advance and 3.68 cubic meters per meter per 

 year unit volume gain. Profile lines within the groin field had a shore- 

 line advance of 3.45 meters per year and gain in unit volume of 11.92 

 cubic meters per meter per year. These figures include directly placed 

 beach fill. Profile lines west of the groin field showed a shoreline 

 advance of 0.66 meter per year and a unit volume loss of 0.12 cubic meter 

 per meter per year (Table 3). The changes on profile lines 1 to 4 are 

 presumed to be the least influenced by the downdrift groin field and 

 beach- fill projects. However, even these values include an unknown amount 

 of material placed on the beach updrift (east) of profile line 1 from 

 maintenance dredging of the Intracoastal Waterway. 



These data show that the groin field at Westhampton Beach is effec- 

 tively trapping sand. During the last 18 months of the study the three 

 easternmost compartments, which were essentially filled, were still 

 trapping sand above MSL at an average rate of 18 cubic meters per meter 

 per year (Table 4) . During the same interval the beach downdrift of the 

 groin field (profile lines 10 and 11) lost sand at an average rate of 

 20.8 cubic meters per meter per year, with the shoreline retreating at 

 6.7 meters per year. 



33 



