The influence of wind and waves on the existence of stable intertidal morphology in meso-tidal estuaries

- We model hydrodynamics in 4 morphologically distinct basins, supported by empirical data.
- The model is used to investigate sediment transport due to waves, wind and tides.
- The formation of in-filled, vegetated intertidal areas is likely under tides alone.
- Waves allow the development of a deeper, hydrodynamically maintained estuarine shape.
- Winds substantially modify circulation patterns.

Most theories on the stability of estuarine morphology highlight the dominance of tidal asymmetry in controlling the morphological stability. Numerical modelling experiments over a series of morphologically different idealised estuaries show that wind and waves are far more efficient than tides at eroding intertidal areas, with the effect being subtly dependent on the depth distribution in the intertidal. Moreover, the wind and wave climate can substantially alter the hydrodynamic regime over the entire estuary and in intertidal areas can exert much greater control on asymmetry than tidal currents alone, which dominate the deeper channels. The strong influence of waves on the intertidal hydrodynamic regime means that the depth profile, around which the intertidal morphology stabilises, is highly dependent on the presence of wind and waves. Under tides alone, the currents over intertidal flats will remain flood-dominant causing continued accretion until tidal currents become too weak to entrain sediment. Therefore, estuaries with only tidal currents are likely to evolve into in-filled salt-marshes with drainage channels, whereas fetch-align estuaries have a greater probability of attaining deeper hydrodynamically maintained stable intertidal areas.