Validity and Limitations of Different Transport Models with Particular Reference to Sediment Transport

Abstract

Abstract The consequences of successive simplifications (Fig. 1) made on the transport equations in order to obtain simpler and less detailed models, are examined. After a review of surface flow models (transport of mass and momentum) with constant density (Fig. 2), the transport models of a neutrally buoyant tracer are discussed (Fig. 3). Groundwater flow and groundwater tracer transport models are also considered and the approaches for modeling transport processes in stratified flows are mentioned. Afterwards, a survey of sediment transport models is made, stressing the effects of space and time averaging. Starting from the most general three-dimensional model of suspension, a one-dimensional unsteady model is obtained, aimed at simulating short time-scale processes both with uniform and non-uniform grainsize distribution. The quasi-steady onedimensional model (averaged over the hydrological cycle) is discussed, considering at first different grainsize classes and then all the classes altogether in the overall transport.