Rate of Sea‐Level Rise and Sediment Characteristics Modulate Deltaic River‐Tide Interactions

Abstract Due to sea‐level rise, small river‐dominated deltas (<100 km 2 ) are expected to become more exposed to tidal influences in the future. However, there remains a knowledge gap in the impending hydrodynamics of such deltas, particularly with the interactions between river and tidal flows. In addition to sea‐level rise, river‐tide interactions in these deltas depend on their morphology, which is influenced by the sand proportion in the particulate matter delivered by rivers. This study investigates river‐tide interactions predicted for small deltas formed by different sand‐to‐mud ratios under various sea‐level rise scenarios. Delta morphologies were generated using reduced‐order complexity model (DeltaRCM), and hydrodynamic simulations were performed using advanced circulation (ADCIRC) modeling. The findings indicate that sea‐level rise promotes deeper tidal penetration into deltas. Deltas formed by finer sediments exhibit deeper channels flanked by large natural levees, whereas those formed by coarser sands are characterized by shallow channels with smaller levees. Consequently, tides primarily propagate along the channels of deltas formed by finer material, while deltas formed by coarser material experience greater tidal inundation. The findings are meaningful toward the adaptive management of deltas.