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. Twenty-one 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.

认识到河流河岸侵蚀的风险是确保早期预警和预防或控制河流流域（包括长江）河岸崩塌的一项重要挑战。本研究介绍了一种基于地貌的算法，通过调整多波束回波探测数据的平坦度来提取河岸侵蚀信息。该算法绘制了十个水下形态元素，包括斜坡、坡脚、平地、山脊、峰、谷、坑、支、空心和肩部。21 个平坦度值被用于构建河岸侵蚀水下特征的解释策略。结果表明，当坡度为10°时，作为侵蚀载体的堤岸被斜坡细胞覆盖。冲蚀坑和堤岸疤痕由靠近堤岸的凹坑单元和平坦度为 0° 的堤岸坡度中的空心单元表示。河流水下沙丘被认为是加速河岸侵蚀的一个重要因素，尤其是那些靠近岸脚的沙丘；沙丘临界平整度评价为3°。分析了水下形态元素的分布，并将其用于绘制河岸侵蚀库存图。分析结果表明，近岸区水深较大，易形成较大的冲坑和较长的岸坎。弧形坍塌往往发生在长岸陡坡上，以缩短其长度。讨论了陆地、海洋和河流环境中平坦度值的不同分配，得出结论，多样化的平坦度值显着有助于河流水下形态识别。