Control of channel geometry on centennial morphological evolution of deltas: A numerical simulation perspective

Delta morphological evolution, shaped by fluvial-sediment processes and human activities, is critical for estuarine-coastal ecological protection. While river discharge and sediment inflow are known to influence delta development, the century-scale effects of river morphological changes remain insufficiently understood. This study investigates the 350 years evolution of river deltas under runoff-tidal dynamics, using the Hydraulic Geometry Coefficient (HGC) to quantify river morphology and a Delft3D-based hydrodynamic-sediment-topography coupled model to assess HGC impacts. Validated against the Paraná and Danube deltas, results confirm HGC as a pivotal control on delta stability and channel configuration: high HGC (wide-shallow channels) facilitates complex multi-distributary deltas, while low HGC (narrow-deep channels) leads to simpler, narrower forms. HGC's influence on riverbed fluctuations is time-dependent—weak initially, nonlinearly enhanced in the medium term, and weakened over the long term—with braided river complexity positively correlating with HGC. A critical morphological threshold (HGC = 5–10) and an “system memory effect” are identified: early morphological differences (e.g., channel estuary count) persist for centuries, with high HGC deltas maintaining complexity and low HGC deltas degenerating into single-channel systems. These findings highlight the significance of channel characteristics in delta formation, offering critical insights for estuary management and delta conservation.