Salinity-induced stratification impacts tides in estuaries

Salinity-induced stratification is common in estuaries, yet its effect on tidal propagation is not systematically quantified and depth-averaged models generally neglect it. Using idealized numerical simulations across well-mixed, partially mixed, and salt-wedge regimes, we show that stratification suppresses turbulence and reduces effective bed friction, weakening tidal damping and allowing tides to penetrate farther upstream. Stratification-induced partial reflection at the landward salt-intrusion limit further amplifies tides, locally increasing tidal ranges by ∼ 30% in salt-wedge estuaries. Depth-averaged models can reproduce these effects through reduced roughness. Results highlight the critical link between salt dynamics and tidal water levels with implications for flood risk management.