Hello,
I would recommend you try doing this in python instead of MATLAB. Indeed TELEMAC now runs with python scripts and more and more feature are added every day in the python library. It would be nice if you can share your work with us then.
Note that the python scripts currently coded under future v6p3 now have very fast and efficient ways at getting cross-section values from a result.
If you real like MATLAB, I would recommend you have a look at some of the MATLAB tool for TELEMAC, from this site under Download => Supporting Tools.
Hope this helps,
Sebastien.