important geological process since it provides a mechanism for barrier 

 islands to move and to increase in elevation. Correct identification of 

 potential overwash areas is also important in the determination of V-zones. 



25. Most overwash research has been geologic in nature, with few 

 engineering studies having been made. A comprehensive evaluation of the 

 literature was conducted and, to the authors' knowledge, no analytical model 

 of the overwash process exists except that developed in an M. S. thesis by 

 Williams (1978). However, the laboratory tests and theory of Williams were 

 inconclusive. Neither the two-dimensional (2-D) dune response to overtopping 

 nor the three-dimensional problem associated with dune breaching has been 

 adequately studied to permit numerical simulations of the overwash process. 

 The Multiple Shore-Breaking Wave Transformation (MSBWT) model of Balsillie 

 (1984c, 1985b) has provision for determining wave heights over both breached 

 and flooded profiles as well as a mechanism for estimating overwash 

 deposition, but the model is not fully operational or verified. A detailed 

 discussion on this model is given in Part III. Other studies quantify the 

 percentage of island overwashed (Pierce 1969, and Boc and Langfelder 1977) or 

 address volumetric changes (Schwartz 1975, and Leatherman 1976, 1981). The 

 results of the literature survey, together with a summary of overwash 

 knowledge for specific case examples, are contained in Appendix A. A 

 procedure for accounting for overwash in V-zone determination is discussed in 

 Part VI. 



Equilibrium Beach Profile Concept 



26. It is evident to the most casual observer that the beach profile 

 has an apparent constancy of shape. When we visit a particular beach, the 

 profile looks more or less the same, year after year. This is most easily 

 explained using the concept of an "equilibrium profile" which continually 

 evolves to be in equilibrium with whatever wave and water level conditions 

 exist. This concept is fundamental to existing predictive models of dune 

 erosion. 



* Information obtained from personal communication with J. H. Balsillie, 

 Division of Beaches and Shores, Florida Department of Natural Resources, 

 Tallahassee, Fla., June 1986. 



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