reasonable degree of reliability, the physical processes under a different set 

 of conditions, provided the latter set is not radically different from the 

 first. Thus the model Is usually calibrated and verified for previous or 

 existing conditions and used to predict future plan conditions. 



7. In the study described herein, the coastal processes for St. Marys 

 Inlet and the surrounding area of the Atlantic Ocean were modeled using the 

 CIP numerical modeling system on two computational grids. The system includes 

 the US Army Engineer Waterways Experiment Station (GEWES) Implicit Flooding 

 Model (WIFM) for tides, the Regional Coastal Processes Wave Propagation Model 

 (RCPWAVE) for waves, the model CURRENT for wave-induced currents, and a sedi- 

 ment transport model for transport of noncohesive sediments due to the com- 

 bined action of tides, waves, and wave-induced currents. All four models 

 generally used the same computational grid for a given set of conditions (base 

 or plan) . The following paragraphs highlight the important features of the 

 computational grids and the four computer models used in this study. For con- 

 venience the numerical modeling system, together with the computational grids, 

 was referred to as Model B in contrast to Model A, a hybrid model used for 

 studying the region interior to the inlet. 



Computational Grids 



8. 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 

 allows 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 com- 

 putational space (Figure 2) . The transformation has the following form: 



c 



X = a + b a P (1) 



p p 1 



y = a + b a-^l (2) 



q q 2 



11 



