Wind-Wave Resuspension, a Controlling Mechanism for Cohesive Sediment Transport within a Shallow Coastal Embayment

The dynamic interaction between wind-waves and cohesive sediment beds is a key sediment transport mechanism within shallow coastal zones. Understanding the contribution of these processes in fine sediment cycling is particularly difficult, owing to the range of compounding biogeochemical processes, seasonal variability and small temporal scales at which they occur. Our research aims to quantify the contribution of wind-waves to transportation processes of cohesive sediment, through the application of fine scale in-situ monitoring techniques. The study area was located within Moreton Bay, Queensland, Australia, a coastal zone subject to significant changes in geomorphology, water quality and subsequent ecosystem health. Terrestrial sediment loading and distribution of fine silts and clays throughout the bay was driven by periodic flood events consistent with the sub-tropical climate. Large fluvial inputs during these events results in a widespread distribution of fine sediments throughout the bay, with considerable quantities deposited within intertidal and shallow subtidal regions.

Our observations focused on fine scale turbulent measurements, in-situ suspended sediment particle sizing, suspended sediment concentrations and changes in bed elevation during two monitoring periods. The first investigated the contribution of dominant northeasterly wind-waves consistent with summer wind patterns and the other an extended period of extreme wind-waves associated with a storm event. The results indicate pronounced differences in the rates of fine sediment resuspension and transportation from monitored sites, highlighting both the temporal and spatial variability in wind-wave driven transport processes. Locally generated sediment fluxes were distinguishable from large-scale advective processes, providing estimates for the net transport rate from these monitored sites. The findings are important for quantifying the reduction in fine cohesive sediment storage within shallow areas of Moreton Bay; processes linked to the rapid recover of benthic habitats in the wake of major flood events.