This paper details the extension of the sediment transport and morphology model SISYPHE to include a lag term within the bed exchange source term of the, depth-averaged, continuity of sediment concentration equation. This lag term represents the time it takes for a sediment concentration profile to adapt to spatial or temporal changes in the flow. The inclusion of a lag term means that the settling velocity is no longer the only scaling factor for the exchange of sediment between the water and the bed. The modified sediment transport and morphodynamics model is tested against field data from the Thames estuary (UK) and on the morphodynamic development of a dredged trench in flume experiments. It is illustrated that the lag factor introduced is essential to model the sediment transport and morphodynamics, especially when considering engineered situations, where the bed is out of equilibrium with the flow conditions. Moreover, with this lag factor included, there is evidence that SISYPHE can be used for morphodynamic modeling of engineered situations.
