Predicting the occurrrence of dunes under supply limited conditions

If only a part a the bed sediment is being transported by a river erosion resistant layers can develop. The presence of erosion resistant layers in the river bed can limit the volume of sediment available for bedform formation. These conditions develop if the flow is not capable of transporting all present grain size fractions. Different bedform types develop depending on the volume of sediment that is mobile. In this paper we combine data from previously published experiments to explore the possibility to predict the occurrence of dunes under partial transport conditions using a parameter s*, the relative sediment transport rate. Herein, we use a model to make reliable estimations of s*. We find that a critical s exists so that dunes only occur for s*>s*cr. The results of the model and the critical s* for dune occurence are validated quantitatively and qualitatively using two sets of experiments, experiments conducted by Van der Zwaard (1974) and a recently conducted set of experiments at the Leichtweiß-institute, Germany.