Hydrodynamic impacts of bridge construction and land reclamation on water residence time and flushing processes in...

Over the past few decades, Kuwait Bay has experienced significant water quality decline due to growing anthropogenic pressures, including oil and gas extraction and extensive coastal developments, leading to severe eutrophication and marine life mortality. Additionally, the recent construction of a 36 km-long causeway across the Bay and related land reclamation projects has disrupted the Bay's natural flushing processes, allowing pollutants and excess nutrients to accumulate more readily. However, the impact of these new infrastructures on the Bay's circulation patterns and water renewal capacity remains unquantified. Here, we use the multi-scale ocean model SLIM to simulate the fine-scale flow patterns in Kuwait Bay and evaluate water residence time distribution, focusing on its spatial and seasonal variability. By further comparing pre- and post-construction scenarios, we quantify the causeway's influence on Kuwait Bay's hydrodynamics and flushing properties. We find a complete renewal of the Bay within 150-320 days, driven by significant spatial and seasonal variations in water residence time, largely influenced by the prevailing winds and strong tidal flows interacting with the Bay's shallow depths. The introduction of the artificial structures extends the average residence time by only 1.29 days (+3.49 %), but with significant local variations ranging from -66 to +56 days, underlining the causeway's role as a physical barrier, and amplifying the risks of water quality degradation in some regions. From a broader perspective, our findings highlight the large-scale impact of fine-scale hydrodynamic changes in a semi-enclosed coastal system on its flushing processes and water quality.