Search Results (2)

Coastal waters, particularly in micro-tidal estuaries, are highly vulnerable to water quality changes driven by salinity intrusion. Effective coastal water management requires a detailed understanding of the dynamic processes in estuaries to mitigate the effects of salinity intrusion. This study focuses on the Brisbane River estuary (BRE), Australia, to investigate salinity intrusion and flushing time under varying freshwater inflows. A coupled MIKE 21 FM hydrodynamic (HD) and transport (TR) model was used to assess salinity transport during a neap–spring tidal cycle. The 2D model was calibrated and validated for the 2008 and 2011 flow events using field data on water levels and salinity. Results show an increase in tidal amplitude landward under low river flow conditions, while tidal damping was observed under higher river discharge, reducing the BRE salinity during spring tides. This study found that salinity intrusion is highly sensitive to freshwater availability, with river discharges of 150 m³/s and 175 m³/s identified as critical thresholds to maintain salinity levels below 1 PSU at the estuary mouth during ebb and flood tides, respectively. Flushing time analysis indicates that the BRE takes approximately 302 h to completely displace saline water when the river discharge is optimized at 150 m³/s. Modifying the BRE estuary mouth—through channel widening or deepening—enhanced the flushing process, significantly reducing salinity levels. This study demonstrates that optimizing freshwater discharge and modifying the estuary mouth can provide effective solutions for managing salinity intrusion in micro-tidal estuaries. Full article

The classification of a lagoon as a restricted lagoon is shown to depend not solely on its geometry but also on the tidal hydraulics. By numerically simulating the tidal exchange of two lagoons of similar geometrical dimensions, the Nidova lagoon and the Papas lagoon, in Western Greece, subject to very similar tidal forcing, applied to the two tidal inlets in the first case and three in the second, very different residence times are found, namely 2.5 days for the Nidova and 25–30 days for the Papas lagoon. This large difference is attributed to the fact that whereas the Papas lagoon functions as a typical restricted lagoon, in which the water renewal is achieved by mixing in the lagoon of the tidal prism water exchanged within a tidal cycle, the Nidova lagoon functions as a flow-through system because of the differential arrival of the tide at its two tidal inlets. It is suggested that this way of enhancing the flushing rate of a lagoon be considered, whenever possible, when creating a new tidal inlet to the lagoon. Full article