Sediment concentration profiles and transport dynamics near the Port of Brisbane, Moreton Bay, Queensland

Dredge operations and relocation of dredge material are important to maintain navigable port facilities. However, the fate of dredge material after relocation is often unclear and requires intensive monitoring strategies. A LISST-100X instrument deployed at the dredge material placement area close to Mud Island (MI) within Moreton Bay, Queensland, reports suspended sediment concentration (SSC) and particle size distribution (PSD) in-situ between September-January, 2016-2017. Tidal driven SCC levels were monitored in the range of 10-35 µl/l with a preliminary analysis of wind-wave events showing no significant impact on SSC levels in the area during a 50km/h (West-Southwest) event. The LISST-100X has allowed for rapid profiling during a dredge dump event comprised of fluvial sediment (d50 = 15-30 µm) from within the Port of Brisbane (PoB). SSC levels 40-90 µl/l higher than those observed prior to the dredge placement are influenced by a bi-directional (Northwest-Southeast) tidal current velocity field on the 15th of November. Temporal and spatial monitoring of 5 sites close to MI indicate a predominant Northwest dispersion of the dredge plume during ebb tide, with its dispersion path hypothesised to intersect a neighbouring commercial shipping channel. These findings will have direct impact on current dredging strategies as well as longterm environmental management concepts in this highly active and sensitive embayment.