Boundary Forcing and a Dual-Mode Calculation Scheme for Coastal Tidal Models Using Step-Wise Bathymetry

by James K. Lewis, Ocean Physics Research &, Development, Long Beach, United States,
Y. Larry Hsu, Ocean Physics Research &, Development, Long Beach, United States,
Alan F. Blumberg, Ocean Physics Research &, Development, Long Beach, United States,

Document Type: Proceeding Paper

Part of: Estuarine and Coastal Modeling


Tidal energetics are persistent and important factors in almost all coastal regions. As such, it is important to employ techniques that can consistently reproduce observed tidal variations. Here we discuss two techniques for the tidal forcing of regional coastal models. The first deals with boundary forcing using tidal amplitudes and phases from observations or from a coarser grid (larger scale) model. It is shown that the Reid and Bodine (1968) open boundary formulation is quite effective as a method for the forcing of a regional tide model. The forcing can be easily tuned, but in most cases the boundary formulation results in amplitudes and phases that are within 10% of observed amplitudes and phases. Some limitations for employing the Reid and Bodine formulation exist, and these are presented and discussed. The second technique deals with the use of a step-wise approximation for the bathymetry of a region employed by many three-dimensional coastal models. This can introduce problems since the tidal wave propagates at (dG) 1/2 and the depth D is only approximated by the step-wise bathymetry. The resulting predicted phases can be off considerably. It is shown that a simple dual mode calculation scheme can account for the differences between the step-wise and actual bathymetry. The model is run in a barotropic mode first using actual bathymetry and then a baroclinic mode using the step-wise bathymetry. By adjusting the baroclinic transports to match the barotropic transports, the effect of the step-wise bathymetric approximation can be minimized.

Subject Headings: Scale models | Approximation methods | Three-dimensional models | Tides | Grid systems | Ocean waves | Computing in civil engineering | Mathematics

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