Larson (1991) described the profile of equilibrium as occurring when: 

 "A beach of specific grain size, if exposed to constant forcing conditions, 

 normally assumed to be short-period breaking waves, will develop a pro- 

 file shape that displays no net change in time." 



Dean (1991) listed four characteristics commonly associated with equi- 

 librium beaches: 



a. They are usually concave upwards. 



b. The smaller the sand diameter, the more gradual the slope. 



c. The beach face is usually planar. 



d. Steeper waves result in more gradual slopes. 



Pilkey et al. (1993) contend that the profile of equilibrium equation is 

 inadequate to define the inner shelf profile shape and therefore should not 

 be used as a basis for predictive models of profile evolution. First, 

 although the equation provides an average irmer shelf profile cross sec- 

 tion, it does not effectively describe the true profile shape as it tends to 

 ignore the effects of bars, and oversimplifies wave-inner shelf interac- 

 tions. However, the equation does provide a useful guide particularly for 

 long-term response of the "average profile." Secondly, the inner shelf is 

 composed of various sediment grain sizes. The assignment of a value of 

 0.67 to the variable n in the profile equation, thus leaving a smaller range 

 of values of the sediment scale parameter A (of 0.0 to 0.3), implies that 

 beach profile shape can be calculated from sediment characteristics (parti- 

 cle size or fall velocity) alone. 



Pilkey et al. (1993) state that the profile shape of the inner shelf is due 

 to many factors, including the following: 



a. Wave climate (particularly the frequency of big storms). 



b. Sediment supply. 



c. Rate of shoreline and inner shelf retreat. 



d. Surficial sediment grain size. 



e. Underlying geology (Figure 3). 



Depth of Closure ^ 



The model proposed by Bruun (1962) concerning shoreline change in 

 response to rising sea level also introduced the concept of depth of clo- 

 sure - "the point on the equilibrium profile beyond which there is no 



Chapter 2 Inner Shelf Concepts 



