Hello,

I am working with an island-wide coastal model (all open boundaries).

I would like to specify a tidal boundary using the Riemann boundary type. I have tested a model with a water level boundary condition using astronomic constituents and a zero-velocity (normalvelocitybnd) condition (to prevent jets from shooting in from the boundaries, which they were in a previous iteration). The results look good compared to tide gages.

However, I would like to use the Riemann option. I don't have a lot of information on how this type of boundary is implemented in FM. The Delta Shell GUI shows the Riemann boundary with units m/s, but the examples in the manual and example models show that it is implemented as a water level (velocity computed with linear theory). As a test, I used the same tidal constituents from my water level boundary (waterlevelbnd) and the results were amplified tidal oscillations compared to the basic water level + zero velocity model run.

Could I get some guidance on how to generate this boundary condition? The boundaries are in deep water, and I should not be getting significant reflection at the boundaries (small perturbations).