Comparison of sediment resuspension measurements in sheared and zero-mean turbulent flows

There are multiple processes at different scales that produce turbulent mixing and sediment lift off in the ocean bottom. Basic aspects of buoyancy and stratification in turbulent flows are used to investigate the lift off of sediments and we describe here some of the innovative techniques used in the laboratory. The present paper describes some of the work that our group has performed within the European Land Ocean Interaction Studies (ELOISE). Further, in a fully detailed paper, a presentation of all the experimental work as well as their results will be submitted. We present in this paper two laboratory experiments with the results of sediment lift off under sheared and zero-mean flow turbulence. We compare actual seabed sediments extracted from the Gulf of Lyon. Comparison is made between the boundary Reynolds stress derived from turbulent r.m.s. velocity, u′, in the zero-mean flow turbulence, and from the friction velocity, u* (Shields critical parameter) in the shear-induced turbulence flow at the sediment laden bottom boundary layer. There is an increase in the sediment lift-off as boundary Reynolds stress increases, whereas there are important differences between zero-mean and shear-dominated boundary flows. Lower boundary Reynolds stresses are required in zero-mean flows to lift off a sediment bed of equal characteristics than in shear-induced flows, indicating the dominant role of r.m.s. velocity fluctuations at the sediment bed.