FM model Bathymetry and computation domain

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Abdulla Mohamed, modified 8 Years ago.

FM model Bathymetry and computation domain

Youngling Posts: 6 Join Date: 5/24/16 Recent Posts

hello everyone,
I recently converted a delft3D model into a delft3D-FM model and am trying to simulate it in the new GUI.
In delft3D "non-values" for bathymetry are defined as -999. I am wondering if this is true in the case of the FM model as well.
Is FM model going to ignore bathymetry points with -999 during the interpolation process?
If I am not mistaken, in delft3D the grid enclosure file defined the flow computation domain for the model.
Is there an equivalent in the FM to define the flow computation domain for the model?
The FM grid I am working with extends over land, and I am wondering how to tell the FM model not to go beyond a certain boundary for computations as it is land.
Is this accomplished in FM by the land boundary file?

Any help on this will be much appreciated.

Thanks in advance.

Cheers,
Abdulla.

Erik de Goede, modified 8 Years ago.

RE: FM model Bathymetry and computation domain (Answer)

Youngling Posts: 16 Join Date: 1/7/11 Recent Posts

Dear Abdulla Mohamed,

*) For Delft3D-FLOW the bathymetry file is in ASCII format and the data is stored for the whole MMAX*NMAX domain. Consequently, a lot of "-999" appear in non-computational points. For Delft3D FM this is completely different: the file is in NetCDF format and only bathymetry values for computational points are stored. So, the "-999" values are not an issue for Delft3D FM. They are absent!
*) In Delft3D FM there is no enclosure file yet. So, you cannot 'abuse' the enclosure file to reduce the computational domain.
*) The standard procedure is to apply dry points, both in Delft3D 4 and Delft3D FM. So, you can extent your model domain to areas on land. For example for flooding studies. By inserting dry points, these points become non-computational (and do not require any computation time and are not visible in plots anymore). The land boundary file has no effect on this.

With kind regards,

Erik de Goede
Deltares

Arthur van Dam, modified 8 Years ago.

RE: FM model Bathymetry and computation domain

Youngling Posts: 2 Join Date: 3/3/11 Recent Posts

Erik de Goede:

[..] For Delft3D FM this is completely different: the file is in NetCDF format and only bathymetry values for computational points are stored. So, the "-999" values are not an issue for Delft3D FM. They are absent!

Actually, it is slightly different. Bathymetry values of -999 are indeed less frequent in Delft3D FM, because you don't need to have any computational points outside region of interest. Still, if you create a new grid, it will have no bathymetry values yet on the computational points, so these z values are written as missing values -999 into the _net.nc file. Later, in the spatial editor in DeltaShell you can replace these by interpolated bathymetry data.
NOTE: if some of your bathymetry values still contain missing values -999 when starting a simulation, Delft3D FM will replace the bed levels of those grid cells that have no bathymetry on any of its corner points to the value of parameter BedLevUni (in DeltaShell via "Physical Parameters > Uniform bed level").