Morfología de perfiles de ríos en roca. Control tectónico y significado evolutivo en el Bajo Guadiana

Abstract

Bedrock rivers are increasingly becoming of interest due to their significance in controlling upstream entrenchment by fixing the base level. Longitudinal profiles are dependant not only of discharge but also on incision capability due to bedload transport thresholds determined by gradient availability. The lower Guadiana River incises into the large Extremadura-Alentexo planation surface, developing large canyon carved on extended flat rocky benches with internal channels. Their development cannot be understood as that of simple hydrodynamic features produced and backwards erosion by lithologic control. In order to determine drainage network evolution in relation to regional surfaces and tectonics, longitudinal profiles river profiles from the Guadiana River and its tributaries have been reconstructed and their concavity index and mathematical fitting curves analysed. Different reaches might be interpreted on a morphostructural framework, with convex river profiles adjusting to active base level lowering as compared to the more stable and better evolved upstream rivers. To explain the convexity towards the south, one must consider the subsidence of the Guadalquivir flexure, which coincides roughly with the Guadiana mouth