appears to be coincident with the occurrence of longer waves during that 

 month (Fig. 16) . Figure 17 gives averages of the monthly mean shoreline 

 position and unit volume data shown in Figure 13, excluding profile lines 

 8 and 9. As discussed previously, the averages shown for July are based 

 on only three surveys and may not be representative of average conditions. 

 The surveys at Westhampton Beach have shown that short-term (less than 1 

 year) fluctuations in beach width of at least 60 meters can be expected 

 away from the influences of the groin field. Changes within and downdrift 

 of a new groin field can be much greater. 



Profile envelope plots in Appendix E show the maximum excursions of 

 •the MSL shoreline and the maximum and minimum elevations measured along 

 each profile line. The envelopes for profile lines 1 to 11 represent the. 

 "active" sand lens over the full 11-year study; the envelopes for profile 

 lines 12 to 20 represent the active sand lens over the last year and a 

 half of the study. The envelopes for profile lines 8 and 9 include the 

 two beach-fill projects; envelopes for profile lines 5, 6, and 7 show 

 the effects of impoundment by the groin field. 



3. Coastal Engineering Implications . 



The beach profile data in this report principally reflect the artifi- 

 cial changes resulting from placement of the groin field and associated 

 beach fill, which began in July 1965. Profile changes measured before 

 the groin field construction were definitely influenced by both natural 

 and artificial (dune and beach fill) recovery from the effects of the 

 March 1962 northeaster. 



The data show that, on the average, the groin field and beach-fill 

 projects have halted an erosional trend at Westhampton Beach. However, 

 the groin field has also had the effect of focusing the erosion problem 

 on the beaches immediately downdrift (west) . After completion of the 

 first 11 groins, the shoreline immediately downdrift of the westernmost 

 groin eroded at a rate of approximately 28 meters per year. This condi- 

 tion was halted by the placement of beach fill and the construction of 

 additional groins. However, the problem was only moved to a new location- 

 immediately downdrift of the extended groin field. In planning such a 

 project, consideration must certainly be given to the potential for severe 

 erosion and property damage at the downdrift end of a groin field. Sand 

 that is removed from the longshore transport system and deposited within 

 the groin field is replaced at the expense of the beaches and dunes imme- 

 diately downdrift. A periodic, local beach nourishment scheme might be 

 one way to maintain the shoreline position and protect the beach in this 

 critical area. 



Visual observations of breaker direction suggest that reversals in 

 net longshore transport direction occur during the months of June through 

 September. Reversals in transport direction within the groin field have 

 been documented by the U.S. Army Engineer District, New York (1969). 

 Further evidence of reversal is shown by the changes on profile line 8 

 during the summers of 1965 and 1966 after construction of groin 11 



32 



