FLOW CHARACTERISTICS OVER EQUILIBRIUM AND NON-EQUILIBRIUM DUNES

This paper concerns the coupling between flow, sediment transport and morphological changes of dunes. Its objective is to investigate intrinsic differences between the flow over equilibrium and non-equilibrium dunes that might explain their different behavior. The study is based on a dune development experiment previously carried out at Queen's University, in which equilibrium dunes were subjected to a sudden decrease in flow depth. For the present purposes, the equilibrium dunes in the experiment under consideration were recreated and immobilized, to enable the study of the flow field at equilibrium state, and just after the flow depth was suddenly decreased. It was found that the near bed time-averaged flow characteristics, as well as the near bed streamwise Reynolds stresses do not correlate well with the observed dune morphological changes. This study further suggests that the local bed-load rates and the local bed shear stress are not as strongly correlated as in the case of uniform flows.