Influence of erosive drivers on the morphology of gullies in the Pampa biome, Southern Brazil

Gully erosion is a complex form of erosion with a large environmental and economic impact, causing loss of fertile soil, siltation of rivers, and changes in the landscape and drainage channels, which have impacted the environmental balance of the Pampa biome in Southern Brazil. The complexity of this process leads to the formation of different shapes of gullies. Studying the morphology of gullies and the main erosion mechanisms acting on them is important to understand the erosion process. With high-resolution data from UAV survey and data from fieldwork, the morphometry and the main erosive drivers of three spatially close gullies with different shapes and intensities in the Pampa biome region were analysed. The V1 gully is the largest of the three studied, showing variation in depth and active erosive mechanisms; V2 has the shortest length, the widest cross-sections and the most significant average depths, with mass movements along almost its entire length. V3 has the greatest length, lowest depth and eroded volume because of less intense mass movements and more stable side walls. Even though various factors interfere with erosion mechanisms and the shape of gullies, the type of soil material proved to be a determining factor in the erosion mechanisms. Sandy materials proved to be more susceptible to mass movements, vertical development, and the concentration of faults and fractures, while predominantly clayey materials proved to be more cohesive and resistant to erosion, especially subsurface erosion, resulting in less occurrence of mass movements. The results presented in this work help to understand the accelerated erosion processes in the Pampa biome in Southern Brazil, elucidating the main factors that influence the shape and expansion of gullies, which is extremely important for determining effective conservation practices.