Experimental observation and modelling of roughness variation due to supply-limited sediment transport in uni-directional flow

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.