The effects of long-term land management are pervasive in agricultural areas of the Mediterranean region, where the physical settings of these agricultural landscapes offer environmental hints about historical land transformations. For example, the presence of large gully systems and small badland areas within these agricultural settings is commonly interpreted as the result of human interference with a delicate natural equilibrium, where human alteration of surface drainage patterns may be responsible of gully development on erodible lithological materials (e.g., marls). In this context, the presence of anomalous drainage layouts (e.g., gullies that do not follow the general topographic axis of valleys, gullies that cross obliquely a hillslope, gullies that are initiated in convexities, or in artificial channels) can provide evidence for human-derived origin of these erosive landforms. We explore physical evidences of anthropogenic origin in the distribution of gully systems within the Conca d’Òdena (60 km2, central Anoia basin, Catalonia), a Mediterranean-dry agricultural setting developed over marly soils where surface-leveled and terraced fields alternate with agricultural ditches, large gullies and small badland areas. We identified and digitized a total of 316 large gully systems in the region (approx. 3% of the terrain) using aerial imagery and a LiDAR-based DEM. About 80% of these gully systems exhibited anomalous topographic patterns, suggesting anthropogenic origin. Further application of a semi-automated GIS method for simple landform analysis revealed that combining DEM smoothing and flow routing algorithms can provide satisfactory results for assessing agricultural origin in small-to-medium size gully systems of the region. Overall, these findings highlight the usefulness of GIS-based morphometric analysis for exploring gully origin and point to a significant role of human activities for the formation of large gully systems in agricultural landscapes.

Mariano Moreno de las Heras (1), Florian Lindenberger (2), and Francesc Gallart (3)
(1) Department of Geography, University of Barcelona, 08001 Barcelona, Spain; (2) Department of Hydraulic Engineering in Inland Areas, Federal Waterways Engineering and Research Institute (BAW), 76187 Karlsruhe, Germany; (3) Institute of Environmental Assessment and Water Research (IDAEA), Spanish National Research Council (CSIC), 08034 Barcelona, Spain.
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