September 2016 Waves and Sediment Flocculation

In the shallow, largely intertidal estuaries that are typical of New Zealand, wind-lashed, whitecapped waves are important. For instance, they scour intertidal flats of mud that is eroded from the land and washed down to the coast during heavy rainstorms, keeping the intertidal flats sandy and clean. Continuing his career research interest in sediment dynamics, Dr Mal Green is currently working with Dr Iain MacDonald of NIWA on an experiment that is aimed at understanding sediment flocculation – the clumping together of fine sediment particles into larger aggregates – in the presence of waves. Over the summer, we will be measuring waves, currents and suspended sediments in an Auckland estuary. We will use a unique piece of equipment called FlocCam, developed by NIWA, to capture high-resolution, digital images of flocs in the water column. The data will ultimately underpin the development of a numerical model of floc dynamics, which will improve our ability to predict dispersal and fate of sediment and any attached contaminants such as metals. The research is funded by the core NIWA research programme Managing Mud.

Green, M.O. and Coco, G. (2014) Review of wave-driven sediment resuspension and transport in estuaries. Reviews of Geophysics, 52: 77–117.
MacDonald, I. T. and Mullarney, J. C. (2015) A novel ‘FlocDrifter’ platform for observing flocculation and turbulence processes in a Lagrangian frame of reference. Journal of Atmospheric and Oceanic Technology, 32(3): 547–561.