open TELEMAC-MASCARET The mathematically superior suite of solvers

Dear friends
I want to simulate the evolution of the river bed where the tributaries meet. The picture shows my topographic cloud map and the simulated bed evolution results. Only the bottom of the river bed is natural in the area I simulate, and both sides of the river are supported by concrete, which is not erodible. How to set the non-erodible area and the erodible area in this case? Can you help me look at the cas file of my model? Please help me check and I'll make some changes.
Best wishes!