Tides, winds, and waves shape the seabed of shallow shelf seas. In sandy, energetic environments, marine dunes can develop. The scale and dynamic behaviour of these bed forms warrant some interest, for example related to the interactions with human activities (mining, renewable energies). Yet, the morphology and dynamics of dunes are still poorly understood in open marine environments. A complex process-based model (http://www.opentelemac.org) is being developed for an application in the southern North Sea, offshore of Dunkirk in France, with the objective to improve our comprehension of the processes at play.