Bathymetry values in output SHEET files

Question

Hello All,

if you run the ROUNDLAKE example as it is, and see the bathymetry in output file such as "sheet_avg.nc" and compare with the actual bathymetry you will notice that they are different. for example at cell (i,j)  16,30 the actual bath is -2.40 but when you see it in output files it is -2.99. Could you please let me know why they are different?  0.59 difference !

what is more interesting is that for some cells the difference are less and for some cells the difference are higher.

for example at cell (2,12) the actual bath value is -0.80 but in output files it is -0.99 so here the difference is just 0.19 !!

 thanks

Mohammad

Answer 1

Hi Mohammed, the bathymetry is actually modified a little in the pre processor.

This is done to limit thin cells which can cause CFL issues and numerical errors.

Chris

Answer 2

I think I find out what is going on about the bathymetry values in output files. It is just calculated based on the dz value for the wet-cell, so if the cell is considered as wet-cell the bathymetry in output is equal to total sum of dz(s) for that cell.

The thing is depth would be calculated based on the output bathymetry+ HEIGHT not actual bathymetry+HEIGHT.

so, one should be careful about calculating depth from output Sheet files.

DEPTH = BATHYMETRY + HEIGHT

I hope to add some information about output data in User-Manual.

Thanks,