Modeling wave-induced sediment transport and morphodynamic response in a bar-built estuary

Abstract

Bar-built estuaries in Mediterranean climates exhibit complex dynamic interactions between wave forcing, sediment transport, and the morphological evolution of the coast. We use phase-resolving FUNWAVE-TVD simulations, forced by time-varying directional spectra downscaled from WaveWatch III/SWAN, to quantify sediment transport and morphological changes in an idealized Marga-Marga estuary in central Chile, under two fixed water levels (SWL and SWL+0.2 m) during a 4-day storm. Spectral analysis shows that infragravity waves (0.003-0.03 Hz) dominate transport variability in the inlet and estuary, with the largest contribution by suspended load and producing similar to 70%-78% of bedload variance. Section-integrated time series in the channel reveal that suspended transport peaks with velocity maxima, whereas bedload peaks during lower-water phases with elevated near-bed shear. The higher water level enhances wave penetration and promotes infilling and retention inside the estuary, while the lower level increases nearshore erosion and breaking-induced stresses. These results highlight the relevance of infragravity motions and suspended transport in governing sediment exchange and estuarine connectivity under microtidal, low-discharge conditions, with implications for the resilience and management of intermittently open estuaries experiencing drought and sea-level rise.