人类改造下河口地貌对洪水响应衰减机制及归因分析OA

Extreme floods are critical natural drivers of estuarine geomorphic evolution.However,how long-term human modifications quantitatively regulate this process remains poorly understood.Although the 2020 flood in the Yangtze Estuary exhibited peak discharge and water levels comparable to the 1998 event,the resulting geomorphic adjustment was significantly reduced.High-resolution bathymetric surveys indicate a 39.5%reduction in deep-channel scouring and a 37%decline in shoal deposition during the 2020 flood.Attribution analysis,integrating hydrological data,long-term tidal records,and numerical modeling,reveals that this dampened response stems not only from shortened flood duration,reduced cumulative flood volume,and weakened tidal dynamics(associated with the 18.6-year nodal cycle),but more critically from reduced sediment supply driven by upstream reservoir operations and over two decades of estuarine engineering.While reduced sediment supply has shifted the estuary's baseline state from net accretion to erosion,estuarine engineering has stabilized the river regime by confining flows to the main channel and inhibiting overbank flow.This promotes a"shoal accretion and channel scouring"pattern,thus optimizing the river regime,stabilizing the shoal-channel configuration,and significantly reducing geomorphic changes during extreme floods.This study clarified how human activities altered the morphodynamic mechanisms of the Yangtze Estuary,significantly weakening the bed adjustment induced by extreme floods.These findings provide a general framework for attributing flood impacts in estuaries worldwide and offer a scientific basis for engineering strategies to enhance resilience to hydrological extremes.