Coastal infrastructure alterations, such as jetty expansions, are designed to provide improvements to natural dredging and safety of marine access and to maximize the management and efficiency of ports. Furthermore, these alterations have the potential to cause significant environmental changes to estuaries and adjacent coastal areas. Here, the hydrodynamics of Pathos Lagoon was investigated before and after the jetty alterations, where the jetty was increased by approximately 10–18% and the mouth width was reduced by 15%. The TELEMAC-3D numerical model was calibrated and validated using the field data, and then simulated for characteristic low and high extreme discharge years for the old and new jetty configurations. Results showed a flow reduction of approximately 20% both in the ebb and flood conditions in the new configuration, which was accompanied by a slight change in the propagation angle of the western jetty current. Reduction of the saltwater intrusion was registered during both the high and low discharge conditions with the new jetty configuration. During the high discharge periods with NE winds, saltwater intrusion did not reach the previous estuarine inland boundary. During the period of low discharge with SW wind, salinity did not reach further than 180 km inland. Reduced saltwater intrusion was estimated landwards and in the shallow embayments. The horizontal stratification structure of the salinity changed, with the partial centralization of the flow in the access channel. The observed hydrodynamic changes from the infrastructure modifications could affect the estuarine ecosystem by increasing the sediment retention, reducing the transport of marine organisms and water properties into the estuary. This study contributes not only to the understanding of hydrodynamic changes but also to the potential optimization of estuarine and coastal management strategies.
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