Benggang erosion: Critical condition and risk prediction in small watershed

Benggang is an erosion landform developed on the deep weathered crust in the low mountain and hilly areas of southern China, characterized by wide distribution and high erosion intensity. Similar erosional landforms globally include the lavakas landform in Madagascar, vocorocas in Brazil, and the "collapse" landform in Japan. However, benggang exhibits distinctive development characteristics that differ from these landforms, thus being considered a geomorphic feature unique to southern China. Investigations into benggang reveal that there are approximately 239000 benggangs in southern China, with a total area of 1220 km². Since 1949, benggang erosion has caused the destruction of 360,000 hm² of arable land, damage to over 500,000 houses, and siltation in around 9,000 reservoirs. This has severely hindered residents' lives and economic development, earning it the moniker "ecological ulcer." Previous studies on benggang have primarily focused on the scale of land blocks or sample plots, identifying elevation, slope, and aspect as key factors influencing benggang erosion. Regional-scale studies have found that geological and pedogenic factors, prolonged and intense rainfall, and vegetation cover significantly impact benggang development. However, research on the critical conditions for benggang formation at the small watershed scale is limited. Therefore, this study focuses on the Yuankengshui watershed in Wuhua County, Guangdong Province. Based on drone photogrammetry technology, digital orthophoto images and digital surface models were obtained, and the boundaries of 296 benggangs distributed in the small watersheds were delineated, including the collapsed walls, alluvial bodies, channels and other parts of each benggang. Then, machine learning and multiple linear regression methods are used to analyze the impact of factors such as altitude, slope, aspect, temperature, rainfall, and vegetation cover on the probability of benggang distribution. Results show that benggang is mainly distributed in the 210-230m altitude range, 23-26 ° slope range, 20-60m slope length range, and most of them are located in the sunny slope. Rainstorm is the main reason for the intensified erosion of benggang. Based on the above research, we have established an information based benggang risk prediction model to explore potential benggang occurrence areas and provide reference for future benggang erosion prevention and control.