The purpose for establishing profile lines 12 to 20 in 1972 was to 

 determine the effects of the groins at various positions within the two 

 easternmost compartments (Fig. 10). The changes in MSL shoreline posi- 

 tion and unit volume for profile lines 12 to 20 are plotted in Figure 

 15 and summarized in Table 4. The shoreline position in the figure was 

 traced from aerial photos taken after the 19 February 1972 northeaster. 

 The change rates in the table were computed by standard linear regression 

 analysis. These data show that, of the three groins, only groin 1 is im- 

 pounding sand on its east (updrift) side and losing sand on its west side. 

 Since most of the impounded sand appears to be removed during periods of 

 erosion, only a small net increase in unit volume occurred updrift of 

 groin 1 between August 1972 and December 1973 (0.5 cubic meters per 

 meter). Profile line 13, immediately downdrift of groin 1, has under- 

 gone a net erosion with some recovery during the summer. Profile lines 

 15 and 16 on either side of groin 2 both accreted, while the two profile 

 lines immediately east of groin 3 showed a net erosion. During the 16- 

 month interval the two compartments gained a total of 17,940 cubic meters 

 of sand above MSL. The compartment bounded by groins 2 and 3 accreted at 

 a rate 86 percent higher than the compartment bounded by groins 1 and 2. 

 The rates of accretion measured on profile lines 14 and 18, located near 

 the midsection of the two compartments, are significantly higher than the 

 average rates for the compartments. Profiles away from the groin field 

 showed little net change during the same period (Fig. 10) . 



Avg. 



(distance-weighted) 



Table 4. 



Rates of 



profile changes 



within groin field, 1972-73. 



Profile line 



Groin 



Distance from 



MSL shoreline 



Above MSL unit 







groin 1 



change 



volume change 







(m) 



(m/yr) 



(m 3 /m/yr) 



12 



1 



63 







-0.54 



+ 0.49 



13 





61 



-6.39 



-4.22 



14 





182 



+ 8.92 



+16.18 



15 



2 



316 

 363 



+4.39 



+27.03 



16 





386 



+18.98 



+37.85 



17 





416 



+24.79 



+62.32 



18 





5 34 



+11.77 



'+26.78 



19 





669 



-6.23 



-0.38 



20 



3 



699 

 726 



-10.52 



-19.01 





1 to 2 





+ 2.37 



+12.76 





2 to 3 





+ 8.51 



+23.71 





1 to 3 





+5.44 



+18.24 



Profile Changes. 



VI. DISCUSSION 



Previous studies of profile changes at Westhampton Beach have deter- 

 mined shoreline erosion rates of 2 to 3 meters per year for data collected 



27 



