PART II: NUMERICAL MODELS 



Introduction 



4. Although in recent years there has been considerable interest in the 

 use of numerical models to simulate coastal processes, models have not been 

 developed that can handle all of the complexities of an actual inlet system. 

 In addition, existing numerical models that consider parts of the overall 

 problem can consider only small idealized problems and not actual spatially 

 large and complex problems. 



5. In order to simulate coastal processes, models must be able to con- 

 sider the propagation of waves over a complex bathymetry, the generation of 

 wave-induced currents (littoral and rip currents), the circulation of tidal 

 and storm surge currents, the littoral transport of sediment, and the response 

 of profiles to wave action by the onshore-offshore transport of sediment. The 

 models must be able to simulate processes over a relatively large area and 

 resolve strong gradients in certain areas (e.g. within surf zone areas). 



6. The models described in this report use the finite difference method 

 for computations. In order to cover a large region but still maintain high 

 resolution in desired areas, the models use a smoothly varying grid that al- 

 lows cells to be small in certain areas (e.g., surf zone or inlet) and large 

 in others (e.g., ocean or sound). A piecewise reversible transformation 

 (analogous to that used by Wanstrath 1977) is used independently in the x and 

 y directions to map the variable grid into a uniform grid used in the computa- 

 tional space. The transformation has the following form: 



c 



x = a +ba. P (1) 



P P 1 



c 



y = a + b <x„ q (2) 



q q 2 



where a , b , c , a , b , and c * are arbitrary constants for regions p 



p p p q - q q 



* For convenience, symbols and abbreviations are listed in the Notation 

 (Appendix A) . 



