PART V: MODELING LIMITATIONS 



124. The numerical models used in this study were the most advanced 

 models available at the time the study was undertaken. However, they do have 

 certain limitations which must be kept in mind in order to view the results 

 obtained from this study in proper perspective. As previously indicated, 

 numerical models represent an approximation to the physical processes. The 

 degree of approximation depends on the physics in the formulation of the indi- 

 vidual models, the resolution of the computational grid, and the time-step 

 used in computation. The assumptions made in the models and the limitations 

 of the models have been given previously along with the description of the 

 models in Part II. In this study, the computational grid resolution and the 

 computational time-steps used have been chosen, on the basis of experience and 

 testing, such that the results obtained would be reasonably accurate for engi- 

 neering purposes and, yet, the computational costs would not be prohibitive. 



125. Generally, the hydrodynamic models are more exact than the sedi- 

 ment transport model because more insight into the hydrodynamics is available 

 and more experience has been gained in modeling the hydrodynamics numerically. 

 With proper calibration and verification, tidal hydrodynamic models such as 

 WIFM can predict tidal elevations very accurately and tidal currents fairly 

 accurately. Monochromatic wave models such as RCPWAVE are fairly accurate in 

 open coast areas. Their results near structures and inlets are more approxi- 

 mate because of the difficulties and expense in modeling diffraction near 

 structures and wave/current interaction near inlets. As for wave-induced cur- 

 rent models such as CURRENT, people have less experience with them than with 

 tidal and wave models. Wave-induced current models are reasonably validated 

 for open-coast situations. Their results are more approximate near inlets and 

 jetties because the hydrodynamic processes are more complicated and less 

 understood, the wave fields are less accurately known, and there is a lack of 

 field data to validate the models. 



126. Sediment transport is the most important aspect of the project for 

 project design; yet the sediment transport model is the least exact of all the 

 models, and the uncertainty is the greatest with this model. The uncertainty 

 exists because sediment transport in general involves complex interactions 

 between the bed and the flow which are not well understood. Of all types of 

 sediment transport, sediment transport near inlets under the combined action 



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