PART V: THEORY OF SHORELINE RESPONSE MODELING AND GENESIS 



96. In this chapter the theory of shoreline response modeling and its 

 mathematical representation in GENESIS are described, including the numerical 

 implementation of major calculation procedures. The physical and mathematical 

 foundation of GENESIS and its internal structure are, therefore, the main 

 subjects. External structural elements for operating the modeling system, 

 i.e., the user interface and input/output files, are described in Part VI. 



97. The basic assumptions underlying shoreline response modeling are 

 first presented, and the equations used in GENESIS to calculate the longshore 

 sand transport rate and shoreline change are introduced. The chapter also 

 gives an overview of the wave calculation model internal to GENESIS. Impor- 

 tant constructs unique to GENESIS, notably the concepts of wave energy windows 

 and transport domains, are discussed, as are boundary conditions and con- 

 straints on the transport rate and position of the shoreline. 



Basic Assumptions of Shoreline Change Modeling 



98. A common observation is that the beach profile maintains an average 

 shape that is characteristic of the particular coast, apart from times of 

 extreme change as produced by storms. For example, steep beaches remain steep 

 and gently sloping beaches remain gentle in a comparative sense and in the 

 long term. Although seasonal changes in wave climate cause the position of 

 the shoreline to move shoreward and seaward in a cyclical manner, with 

 corresponding change in shape and average slope of the profile, the deviation 

 from an average beach slope over the total active profile is relatively small. 

 Pelnard-Considere (1956) originated a mathematical theory of shoreline 

 response to wave action under the assumption that the beach profile moves 

 parallel to itself, i.e., that it translates shoreward and seaward without 

 changing shape in the course of eroding and accreting. He also verified his 

 mathematical model by comparison to beach change produced by waves obliquely 

 incident to a beach with a groin installed in a movable-bed physical model. 



99. If the profile shape does not change, any point on it is sufficient 

 to specify the location of the entire profile with respect to a baseline. 



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