May a single gully evolve from connected and disconnected gullies?

Abstract

The hilly plateau where the basins of the middle Paraíba do Sul River evolve is covered by weathering mantles which thickness is so variable as the local Neoproterozoic bedrocks. Soils in the area have been exposed to the impacts of extensive livestock farming after depletion by coffee plantations during the 19th century, bringing to the present examples of highly degraded slopes. Mapping gullies at the study area led to a conceptual model of gully evolution that predicts the integration between connected and disconnected gullies into a unique long gully. This study presents the actual evolution of a system of gullies that is selected since 1984 for testing those predictions. Records from past surveys are combined with recent measurements, high-resolution UAV photogrammetry and GPR survey, showing the stage of the connected and disconnected gully system in 2023. Due to the method’s high resolution, each gully case brings an in-depth study, drawing associations between Quaternary morphogenesis, slope geometry and gullying. After four decades of monitoring, the gully system is at the threshold of integration. And it still highlights the risks of insufficient diffusion of information about the evolution of gullies and slopes.