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Hello everyone,

I notice something weird when interpolating GEBCO 08 bathymetry into my mesh. Previously, I have successfully run a tidal model using this bathymetry, which give a very good approximation when compared with measured ADCP data. However, when I try to run a new model at different location (quite close to the previous model) , only then I notice that at certain coastline (in red circle), the legend shows a very high values for the depth (kindly see the attached snapshot)

Can I get some advice on why this happened and/or is there any way to eliminate this anomaly?

Some background on what I have done

1. I have used 2 sources of Gebco Bathymetry (from GEBCO Gridviewer and also from Delft Dashboard) to make sure the data is correct. They both show the same anomaly

2. I have tried all interpolation method, which give slight differences, but not much different from one another

3. I have tried to reduce the mesh edge length

From my understanding, GEBCO 08 incorporate both Bathymetry and Topography in their data, but this high value that I get from interpolation just doesnt seem right.

Any advice on this matter is greatly appreciated

Thank you

Hello,

Have you checked if there actually is a GEBCO land point with this height just inside the boundary of your domain?

Regards,
Costas

Hi Costas,

Thank you for your reply.

I double checked everything, and yes, there is a land point + height at the location pointed. From my observation, apparently the GEBCO data is not accurate enough. I extracted my land boundary from Geodas (full resolution) and Delft Dashboard, and I noticed even in Delft dashboard, the bathymetry did not correctly interpolated / matched to the land boundary (kindly refer to the picture attached)

So what I would do right now is to use Matlab to remove any height above 0 from my interpolation file.

Regards
Anas

Hello Costas,

Regarding this topic, do you know how I can change the value of the bathymetry that has been interpolated into the mesh file?

For example, since I know now that I want to eliminate the land values (height > 0) from my mesh + bathymetry, how do I proceed from there?

I have tried to save my mesh (.t3s) as .dat file, then in Matlab, I find and replace all values > 0 = 0. But then I can't find a way to save the edited .dat (mesh+bathymetry) file as .t3s again.

Any guide in this matter is very much appreciated.

Anas

Hi Anas,

There are a number of ways to edit a mesh in Blue Kenue.
In this case I suggest you use the calculator to set a threshold value.

eg. to replace all values > 0 with 0, use the expression a<0.

The < operator in the BlueKenue calculator is called the "lesser of" operator. It returns the lesser of the two operands.

Please refer to the Blue Kenue reference manual (section 1.6.9.2, page 116) for more details.

Hope this helps... Martin

Hi,
Please, who can help me to know how can I assign z elevation values imported to BlueKenue as an (* .xyz) file, to the nodes of "T3 Mesh Generator"? Thank you

Hi
Start by reading the BK user manual!
You should use the interpolator before mapping values on the mesh

Regards