Recognition of Fluvial Bank Erosion Along the Main Stream of the Yangtze River

Recognizing the risk of fluvial bank erosion is an important challenge to ensure the early warning and prevention or control of bank collapse in river catchments,including in the Yangtze River.This study introduces a geomorphons-based algorithm to extract river bank erosion information by adjusting the flatness from multibeam echo-sounding data.The algorithm maps ten subaqueous morphological elements,including the slope,footslope,flat,ridge,peak,valley,pit,spur,hollow,and shoulder.Twentyone flatness values were used to build an interpretation strategy for the subaqueous features of riverbank erosion.The results show that the bank scarp,which is the erosion carrier,is covered by slope cells when the flatness is 10°.The scour pits and bank scars are indicated by pit cells near the bank and hollow cells in the bank slope at a flatness of 0°.Fluvial subaqueous dunes are considered an important factor accelerating bank erosion,particularly those near the bank toe;the critical flatness of the dunes was evaluated as 3°.The distribution of subaqueous morphological elements was analyzed and used to map the bank erosion inventory.The analysis results revealed that the near-bank zone,with a relatively large water depth,is prone to form large scour pits and a long bank scarp.Arc collapse tends to occur at the long bank scarp to shorten its length.The varied assignment of flatness values among terrestrial,marine,and fluvial environments is discussed,concluding that diversified flatness values significantly enable fluvial subaqueous morphology recognition.Consequently,this study provides a reference for the flatness-based recognition of fluvial morphological elements and enhances the targeting of subaqueous signs and risks of bank failure with a range of multibeam bathymetric data.