The performance of an uncoupled numeriacl model of alluvial frlow is compared with that of a coupled model. The uncoupled is the well known HEC6 and the coupled model is the newly developed non-dimensional model of riverine flow called COUPFLEX. The models are applied to the data obtained from some laboratory tests on river sedimentation carried out exclusively for this purpose. The experimental work and procedure are described and the models reviewed. Application of the models to experimental data associated with fast flow and sedimentation processes, reveals the preferability of the coupled approach. The strong inter-relation between water and and sediment components of alluvial flows is recognised in the coupled approach and this gives it advantages over the traditional uncoupled method in which the calculations of the water flow and bed level variations are separated to various degrees. Simulation of several carefully performed laboratory tests highlights three beneficial aspects of a coupled approach. The simulations show that a coupled model (1) gives more accurate results when rapid river processes are involved, (2) obviates some computational difficulties such as production of false bed level oscillations, and (3) allows more flexibilioty in the selection of the size of the computational time step.