Suspended Sediment Transport in Context of Dredge Placement Operations in Moreton Bay, Australia

Abstract

A developed understanding of site-specific sediment transport processes is key for the assessment of coastal works, such as dredging and environmental management. This study investigates characteristics of the suspended sediment regime and sources of turbid water throughout a range of hydrodynamic conditions within a designated dredge placement area in Moreton Bay, Queensland, Australia. Field-monitoring campaigns were conducted prior, during, and post-dredge placements to evaluate the context of dredge material delivery with respect to natural suspended sediment drivers in proximity to the placement site. Elevated wind-wave events (wind velocity > 30 km h−1) were strongly correlated with increased turbidity within shallow regions of the study area, classifying short-period waves as a significant source of background turbidity at the placement site. In situ suspended sediment concentration profiles post-dredging identified steep concentration gradients extending 1.5–3 m above the bed, whereby recently deposited unconsolidated sediment was entrained during the following flood-ebb tidal periods. The use of in situ particle-sizing techniques was instrumental in identifying large low-density flocculated material as the key transport form of fine cohesive fractions. The findings have implications for future dredge placement campaigns and will help to establish more robust assessment criteria for dredging operations. More generally, the observations contribute to understanding post-dredging water quality parameter ranges within dynamic coastal environments, such as Moreton Bay.