1 . Idealized Concept of the Sediment Balance Approach. 



As described by Bruun (1962) a rise in the mean elevation of the water 

 surface tends to shift the equilibrium sand profile landward. As water levels 

 rise erosion prevails on the upper beach and the shoreline retreats. Con- 

 ceptually, the erosion supplies material to build the outer part of the 

 responding profile upward. It is assumed that the initial profile shape is 

 reestablished farther inland and at a distance above its initial position 

 equal to the change in water level z as depicted in Figure 13. Thus, the 

 ultimate retreat of the profile x can be calculated given the dimensions of 

 the responding profiles, X and Z, and a measure of the stability of the 

 shore-eroded material in the outer zone, Ra . 



zX(R^)S8 (^) 



where sg (z) = 1 if z > (i.e., water rising), or sg (z) = 1 if z < 

 water falling. 



(1) 



(i.e.. 



0. Equilibrium Profile 



b. Increase of Water 

 Level and Profile 

 Elevolions 



c. Recession of 

 Profile 



Find "1 



ater Surfoces 



d. Net Results 

 * 2 





w 



-V 



-Eroded 







\ 



r '^ 





\'k- 



\ 



T 





2 















X<^ Deposited 











., ^^,j_^ S 



Closure 









^^^-A. 













1 



Figure 13. Schematized view of profile adjustment 

 as two rigid translations. 



25 



