Cut-and-Fill of Nearshore Bottom 



Studies of the detailed soundings used in the preparation of Figures 

 7, 8, 10, 11, 12, and 13 revealed the following maximum ranges in altitude 

 of bottom level at points out from the MLW shoreline: 50 yards - 6 feet; 

 100 yards - 8 feet; 200 yards - 9 feet; and 300 yards - 12 feet. When 

 Figure 9, for the March 7, 1962 storm is added in, the only range value 

 that is changed is that for the 50-yard position, which is increased to 

 8 feet. Cut-and-fill incident to formation and destruction of bar rhythms 

 seems to be a major factor in determining the magnitudes reported. 



CONCLUDING REMARKS 



Genesis of Beach Changes 



Virtually nothing has been presented in this study relative to the 

 causes of the observed beach changes. This will be presented in another 

 study of this series by W. Harrison and W. C. Krumbein (1964). It is the 

 authors' belief, however, that the descriptive material presented herein 

 will aid students of beach processes, whether they be marine geologists, 

 engineers, or interested laymen. A few observations of possible value to 

 engineers conclude the report. 



Engineering Implications 



The rapidity of beach changes, even under average sea-state conditions, 

 cannot be underestimated. A beach is simply one of the most unstable of 

 all landforms. The daily profiles of Figure 6 provide only minimum values 

 for development of expectable ranges of cut-and-fill, because they were 

 obtained during a period of relatively low energy input for this beach. 

 Ranges of vertical changes for the nearshore bottom are somewhat more 

 dependable. 



Design criteria must, of course, take into consideration the changes 

 to be expected from great storms, which will be many times those of the 

 normal sea-state conditions. It may be inferred from the limited data of 

 this study that under great storm conditions the foreshore slope and beach 

 ridge will undergo greater change than the nearshore bottom. Figures 2 

 and 9 may provide some guidance as to the magnitudes of expectable changes 

 in sand level from great storms. 



Undulatory longshore bar and trough rhythms bear consideration when 

 attempting to design submerged breakwaters. Hom-ma and Sonu (1963) have 

 noted the importance of understanding these rhythms when specifying the 

 length of groins and jetties, while Bruun (1954a) states that sudden 

 shoaling at a coastal inlet may be due to the migration of a large-scale 

 rhythm. 



