Impacts of Sea‐Level Rise on Morphodynamics and Riverine Flooding in an Idealized Estuary

Abstract This research simulates the morphodynamic evolution of an idealize estuary under four different SLR scenarios of increasing severity to investigate how SLR will influence riverine flooding in estuaries. We find that estuarine response to SLR is influenced by both morphological changes to channel capacity and the associated changes to channel hydrodynamics. Low and moderate SLR scenarios result in an increase in flood extent throughout the estuary relative to the no SLR base case. Surprisingly, more severe SLR scenarios result in decreased flood extent in upstream reaches. This shift is due to penetration of tidal energy and erosion further upstream with greater SLR, which increases channel capacity locally. A periodic pattern of local sediment transport is additionally observed due to SLR, which we attribute to the time response lag between hydrological and morphological response. The finding that increased SLR does not result in increased flood extent everywhere emphasizes that flood mitigation measures need to carefully account for non‐linear responses in the estuarine morphodynamic systems, such as the feedbacks resulting from increased tidal erosion.