Hello Philip,
I suggest you to switch to Telemac3d-Gaia (Gaia is the 'new' module for sediment transport which contains latest developments).
Unfortunately the documentation is missing for the test case bosse-t3d even for Gaia. We are working to complete it but in the meantime , if you just want to understand this test case, you can read the documentation of bosse-t2d where shallow water equations are solved instead of Navier-Stokes equation. This test aims to describe the morphological evolution of a dune.
Hope it helps.
Best regards,
Sara