Sorry I misunderstood that you needed to visualize free surface elevation and not water depth.
You can do this in BK, as you have showed above, but another method is to do it in Telemac itself.
Use the routines NOMVAR_TELEMAC2D to give a name to a new variable, and PRERES_TELEMAC2D to define this variable at every node for every time step.
In Fortran you define this variable as <0 (ie =-1) when depth < .05 and equal to the surface elevation when depth > .05. Depth and free surface are readily available in PRERES. This new variable is printed in the result Telemac file and will be visualized with BK.
The advantage of defining this variable in Telemac rather than in BK is that you prepare the fortran procedure to define it in PRERES only once. Otherwise, if you do it in BK, you will have to create this new variable each time for every run.
Another advantage is that, in the Fortran code, you have a trace of the procedure used to calculate this new variable (was it depth<1cm or 5cm?). In BK you do not have a trace of what you did with the calculator.
This is one of the advantages of Telemac: The user can control easily, within the code itself, the input and the output of the model, to suit her requirements.
Thierry