Combined effects of sea level rise and increasing nearshore waves on tidal flat morphodynamics: Implications for future delta management

Tidal flats provide critical ecosystem services for coastal communities in global mega deltas. Understanding how tidal flats respond to climatic stressors is critical for predicting their future evolution and adjusting delta management strategies under global climate change. In this study, we investigate tidal flat morphological responses to varying scenarios of sea level rise (SLR), wave height rise (HsR) and sediment availability, via a morphodynamic model (DET-ESTMORF) based on the Dynamic Equilibrium Theory. The results indicate that SLR promotes increased concavity in tidal flat profiles, while HsR intensifies erosion, driving progressive steepening of the profile. When both factors act simultaneously, tidal flats experience faster landward retreat and elevation decrease, leading to greater profile slope. However, the interplay between SLR and HsR demonstrates an antagonistic nature: their combined impact on tidal flat retreat is sub-additive relative to the sum of their individual effects. Sediment supply plays a pivotal role in buffering these impacts, with sufficient sediment supply enabling accretion and promoting seaward expansion. Dissipating wave energy can also restrain the retreat of tidal flats and potentially reverse erosional trends. These findings underscore the significance of implementing integrated sediment regulation strategies (e.g., increasing riverine sediment flux), combined with nature-based solutions (e.g., wave-damping infrastructure) to ensure the sustainability of tidal flat systems in deltas under climate change.