The relationship between dune geometry and the volume of mobile sediment was studied in flume experiments. In these flume experiments, the volume of mobile sediment on top of an immobile coarse sediment layer was increased stepwise and the bedform characteristics were observed. A strong relationship was found between the volume that is mobile -and therefore available for bedform formation -and the dune dimensions and regularity. If the sediment supply is limited, dunes are smaller and more regular. Series of experiments with a decreasing supply limitation were conducted for different flow velocities and water depths. The relationship between the dune dimensions and the available volume is different for each series. The observed relationships between dune dimensions and layer thickness collapse to one relationship for height and one for length if scaling parameters are introduced. Current models for bedform dimensions under alluvial conditions can be extended to partial transport conditions using this relationship.An experimental study into the geometry of supply-limited dunes 1725

This paper presents a study on the relationship between supply-limited bedform formation and the hydraulic roughness of the riverbed. The results of several new sets of flume experiments with supply-limited or partial transport conditions with bimodal sediment are presented. The results show that both the bedform and grain-related roughness show a clear dependency on the degree of supply limitation. This variation can be attributed to the reduction of the bedform dimensions with a decreasing availability of mobile sediment and an increasing exposure of the usually coarser sublayer (armour layer or pavement) that causes the supply limitation. In the present study, we present a new method to predict the exposure of the immobile sublayer, as well as the bedform and grain-related roughness under supply-limited conditions.

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