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Tidal Boundary Conditions: Riemann

Yahia Kala, modified 2 Years ago.

Tidal Boundary Conditions: Riemann

Youngling Posts: 6 Join Date: 7/11/13 Recent Posts



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).

Xiaohui Wang, modified 2 Years ago.

RE: Tidal Boundary Conditions: Riemann

Youngling Posts: 2 Join Date: 10/2/18 Recent Posts


Have you dealt with this problem? and I am also not very clear of how to add riemann boundary. If you have, can you share with me. Thank you.

Renan Ribeiro, modified 2 Years ago.

RE: Tidal Boundary Conditions: Riemann

Youngling Posts: 5 Join Date: 3/23/11 Recent Posts

Hello everyone,

I am also with similar doubts about Riemann boundary conditions.

It seens that Delft3d-FM have two possibilits of Riemman:

one using waterlevel (riemannbnd option in .ext file) and

another one using velocity (riemann_velocitybnd in .ext file).


The doubt is how calculate Riemann invariant (both: water level and velocity).

Using the same equation to calculate Riemann invariant of Delft3D-FLOW and trying to use riemann_velocitybnd the model doens't run 

and displays the following error message:


** ERROR  : Salinity boundary (partially) unassociated. (   120 points)  Open boundary required.

If I just change the type for riemannbnd the model runs normally, but of course with bad results, because the input files are related to riemann velocity, and itisn't related to riemann water level.