Measuring suspended sediment and its wave and turbulence forcing in the Dee estuary

Coastal areas support many human activities and represent a very important habitat for many marine and bird species. The Dee estuary, located in the eastern Irish Sea, is 20 km long, 8 km wide at the mouth and is characterized by a 10 m tidal range. Suspended and seabed sediments in the Dee contain a diverse assemblage of non-cohesive and cohesive sediments, and therefore the threshold of motion at the bed could be a complex process, dependent on several factors. In this paper, we present data collected during 2 deployments in the Dee, including both acoustic and optical instruments to study the link between the hydrodynamics, turbulence, and suspended sediments. Suspended sediment concentration is clearly controlled by tides following the flood/ ebb and spring/neap cycle. Moderate wave events were observed to increase sediment concentration, though mainly near the bed. High concentrations of silt and very fine sand were found that could support the flocculation processes during the flood and ebb cycle. Sediment concentrations at heights above 1 m from the bed do not present direct relation with bottom stress.