Systematic morphological classification method for cultivated land erosion gullies in the typical black soil regions of Northeast China

Morphological classification of erosion gullies is crucial to assessing their development status and potential hazards. Investigating erosion gullies classification and distribution in cultivated land is essential for comprehensive erosion control and preventing soil and water loss on slopes. The current literature lacks definitive indicators for a comprehensive gully morphology classification system in cultivated land, resulting in incomplete classification outcomes. This study presented a comprehensive framework for organizing morphological indicators, consolidating the essential requirements for managing cultivated land gullies in Northeast China's black soil regions. It employed systematic classification and information science methodologies. Through the combination of indicators which were obtained through remote sensing interpretation, all possible types of cultivated land erosion gullies were covered as much as possible. This framework classified area indicators into five classes, widths into four grades, and lengths into five types, creating a "class + grade + type" method for erosion gullies in cultivated land. The method was empirically evaluated in black soil agricultural zones to confirm its applicability and effectiveness. The findings showed that: (1) Erosion gullies were characterized by small areas, substantial widths, and short lengths in Hailun city's cultivated lands. In the "class + grade + type" framework, class I and II were the most common primary categories. Notably, class II grade 4 tiny gullies (Ⅱ4T) and class II grade 4 small gullies (Ⅱ4S) dominated the secondary and tertiary classifications. These erosion gullies were generally poorly developed and could be effectively controlled by developing high-standard farmland. (2) The morphological distribution of erosion gullies was significantly influenced by terrain elements. Special attention was required for gullies in areas at elevations of 180-<240 m, slope lengths of 35-<55 m, slopes of 2°-6°, and on southwestern slopes. Less developed gullies in these regions, such as class I grade 4 tiny gullies (Ⅰ4T), class II grade 4 small gullies (Ⅱ4S), and class II grade 4 tiny gullies (Ⅱ4T), were prone to advancing to more developed stages like class IV grade 4 medium gullies (Ⅳ4M) and class V grade 4 medium gullies (Ⅴ4M). The study recommended timely and comprehensive prevention and control measures, along with farmland construction, to mitigate potential damage. (3) The “class + grade + type” method developed in this study accurately and intuitively elucidated the morphological features and hazards of cultivated land erosion gullies. This method offered practical advantages, including easy indicator acquisition and simple operation. This research validated that relying on a single morphological index was insufficient for nuanced gully identification. Instead, the robust classification system using area, length, and width indicators demonstrated high adaptability in Hailun city. This innovative method provided a valuable reference for the integrated management of gullies and cultivated land.