Gully erosion and expansion mechanisms in loess tablelands and the scientific basis of gully consolidation and tableland protection

Gully erosion is serious in the tableland area of the Loess Plateau due to high-intensity human activities and extreme rainfall, which cause serious soil loss and an increasing tableland shrinkage rate. Severe gully erosion has exerted a notable negative impact on local agriculture, human life and socioeconomic development. In recent decades, progress has been made in soil and water conservation with the goal of reducing soil erosion and protecting loess tableland, but basic research on gully consolidation and tableland protection (GCTP) is lacking, especially regarding the mechanisms of gully erosion and expansion in loess tableland under the interactive impacts of hydrodynamics and human activities. In addition, there is a lack of a deep understanding of the underlying mechanisms of soil-water disasters and controlling factors of unreasonable GCTP projects. Currently, the problems of headcut erosion and tableland fragmentation remain serious. Based on this situation, the Dongzhi tableland, the largest tableland on the Loess Plateau, was adopted as an example, and we studied gully erosion and expansion mechanisms in the loess tableland and the scientific basis of GCTP projects. We obtained a series of novel findings, including the following: (1) vertical joints are widely developed in loess and impose a controlling effect on tableland edge erosion; (2) rapid urbanization and road network expansion intensify headcut erosion and are the main reasons for severe erosion and tableland shrinkage in the Dongzhi tableland; and (3) unreasonable drainage of surface runoff and a rise in the groundwater level are the key factors affecting GCTP project stability. Moreover, the mechanisms and modes of erosion disasters in the project driven by these two factors were explained. The systematic remediation idea of retention, storage, drainage and consolidation for the GCTP project was introduced, and the core is water control, which emphasizes the combination of soil and water conservation and geohazard prevention measures. As a systematic remediation project, GCTP in loess tableland requires multidisciplinary and multimethod approaches and multiple measures involving ecology, soil and water conservation, geology and engineering to ensure project feasibility and sustainability.