Partial Entrance Restriction as a Potential Tidal Flood Mitigation Strategy in a Large Urban Estuary

ABSTRACT Tidal flooding in estuaries is expected to worsen as sea‐level rise (SLR) continues to accelerate and increases storm surge height. Conventional structural defences are often unsustainable, while nature‐based solutions like managed realignment require extensive land to be repurposed. Although estuary entrance geometry significantly influences tidal propagation, its role in flood mitigation remains underexplored. This study evaluates a simplified mitigation strategy inspired by natural entrance flow constriction using a calibrated 2D hydrodynamic model of the Clyde Estuary, Scotland, under 2100 and 2300 SLR projections. Simulated flow constrictions reduced tidal flood extents by up to 28% and 23%, dampened tidal range by 0.95 and 0.83 m under 2100 and 2300 SLR, respectively, and both delayed peak flooding by 30 min. Sensitivity analysis revealed that wider interventions placed closer to the estuary mouth are more effective at mitigating the effects of 2100 SLR. However, as a larger tidal prism caused by 2300 SLR is more concentrated in the middle estuary, placing interventions in the middle estuary, rather than towards the mouth, is more effective under the 2300 SLR scenario. These findings suggest that strategically placed flow constrictions could offer a scalable and effective tidal flood mitigation option, addressing pressing climate emergency challenges across urban estuaries around the world where alternative approaches to adaptation are not possible.