An examination of all profiles indicated that instead of choosing a single 

 limiting depth, it would be more realistic to pick two depths: the critical 

 depth, a shallower depth above which bottom changes typically exceeded 0.3 

 meter, and the pinch-out depth, a deeper depth below which there was no evi- 

 dence of change. Between the critical and the pinch-out depths there is a 

 small but consistent evidence of aggradation (about 0.2 to 0.1 meter in 4 

 years), indicating transport and accumulation of sediment beyond the barred 

 zone. Beyond the pinch-out depth, changes were haphazard and generally less 

 than 0.10 meter. Which of the two indicators of closure (critical or pinch- 

 out) will be the most relevant depends on the application. For example, when 

 planning a sediment budget the bathymetric surveys should run to at least the 

 pinch-out depth. On the other hand, when selecting a site for placement of a 

 bottom structure or instrument package, going beyond the critical depth may be 

 enough to preclude burial by the normal processes of sedimentation. 



The selection of the closure depths involves an acknowledged subjective 

 evaluation as to where the profiles appear to close at each survey station. 

 The degree to which individual judgment affects these estimates is illustrated 

 in Figure 11 by two estimates obtained independently by two different individ- 

 uals at each of the profile stations. Discrepancies between individuals, 

 while substantial at some stations, do not have an unacceptable effect on the 

 average depth for a broad reach of shore. Thus, attempts to obtain greater 

 apparent objectivity in the selection of the individual depths seem 

 unnecessary. 





























Sfation Nos. 



















,0 5 10 15 20 25 3( 



5 

 6 



1 1 1 1 1 1 



o 





f 



tj) I 



> a 



) 1^ 



7 



- a a 



P 



Q G 



f ' 



> 



i * 







- « 



) 







? 





> 





1 



8 







1 t 



' "r 



p li 

 ; i 



; 







9 







8 



E 9 





[ 



( 



( 





a ■ 



i 



C 



1 

 : 1 



1 







1 ■? 



i B 



( 



> 

 ( 



1 



B 



\ C 



\ •?; 





1 



f ? 



































?? ■• 













jz 









































|,0 



- 



I 



l> 











1 



■ 





; f 



























' I 



1 ; 



' I 



> 









I 







II 



- 







1 



' 













1 



t 



. 





[ 









12 



- 



i 



A 





<^ 



J 









DEPTH OF CLOSURE (m) 







13 



- 





I 



1 1 



( 



I 







Critical depths shown obove 







lA 





Pinch-out depths below 







Figure 11. Dept;hs of closure. Estimates of profile closure were made inde- 

 pendently by two different individuals (represented as D and 0) 

 at profile stations 1 to 29. Solid lines connect their estimates 

 of critical and pinch-out depths at the same stations. At sta- 

 tions where the profile did not extend deep enough to permit a 

 confident selection of the pinch-out depth, a dotted line extends 

 2 meters below che critical depth estimate. 



21 



