After a brief reminder on the sediment composition and facies, the paper reviews water-sediment exchanges that require to account for sediment transformation in Coastal Environment modelling. Physical processes (consolidation, bed armouring, liquefaction) and bio-chemical processes (organic matter mineralisation, adsorption/desorption, precipitation/dissolution, bioturbation…) are briefly reviewed, as well as usual modelling methods. The need for a guide book on the required minimal modelling, depending on the arisen questions, is put forward.