Climate change and entrance channel reconfiguration impacts on a low inflow estuary

Estuaries provide critical ecosystem services, including habitat support, water-quality regulation, flood mitigation, and coastal stabilization, yet these functions are increasingly affected by anthropogenic modifications and climate change. This study investigates the hydrodynamic impacts of entrance channel reconfiguration in a low-inflow Southern California estuary and evaluates how modified inlet geometry interacts with projected sea-level rise and warming scenarios. A high-resolution hydrodynamic model is calibrated and validated using in situ observations of water levels, flow velocities, salinity, and temperature observations pre and post-entrance modification. Numerical experiments with identical forcing conditions isolate the inlet geometric effects, followed by climate-perturbed simulations based on IPCC projections. Results show that inlet reconfiguration increases flow velocities by more than 0.1 m s −1 near the entrance, modifies tidal asymmetry, and substantially alters residence times (exceeding 50% in some regions), salinity and temperature distributions. Sea-level rise enhances ocean–estuary connectivity, amplifying flow velocities and reducing residence times, while temperature increases exert a secondary influence. These findings highlight the influence of engineering interventions and climate change on estuarine circulation and flushing capacity, with important implications for future management and adaptation strategies. • Inlet modification increases flow velocities and alters tidal exchange patterns. • Residence time decreases over 50% in estuarine regions due to enhanced connectivity. • Sea-level rise amplifies circulation and flushing, warming has secondary effects. • Engineering and climate forcing significantly reshape estuarine hydrodynamics.