Resumen de Catchment dynamics in a Mediterranean mountain environment: the Vallcebre research basins (southeastern Pyrenees) II: temporal and spatial dynamics of erosion and stream sediment transport
Francesc Gallart i Gallego, Josep Carles Balasch Solanes, David Regües Muñoz, Montse Soler, F. Xavier Castelltort Aiguabella
Erosion processes and sediment dynamics were studied in a set of Mediterranean mountain catchments with very active badlands during a period of over 10 years. The relatively small badlands produced most of the sediments, whereas both the dense vegetation and the old soil conservation structures impeded significant erosion from the main area of the catchments. The dynamics of the badland surfaces are driven by intense frost weathering in winter, and the subsequent compaction and erosion of the regolith throughout the year. Infiltration rates measured by means of rainfall experiments were found to depend on regolith moisture and density and reached the lowest values in autumn, whereas regolith detachability by splash was higher in autumn and spring. Nevertheless, erosion rates at the plot scale (1430 m(2)) were especially high between May and September due to the role of high intensity rainstorms. The main runoff events at the small catchment scale (1.3 km(2)) occurred between November and January due to the large rainfall events of moderate intensity and the wet antecedent conditions; secondary events occurred in late spring and scattered flash floods occurred during summer. The main sediment transport events occurred in November and December, although less important events occurred in late spring and late summer. As little as 3% of the events produced 73% of sediment yield during 5 years. There was, therefore, a temporal shift of the sediment conveyance with increasing spatial scale: the regolith was produced during winter and, subsequently, eroded during summer, when intense rainstorms produced runoff only on the badland surfaces; nevertheless, most of this sediment was deposited in the channels because the catchment was dry and did not contribute to stream discharge. Subsequently, large flood events produced outside of the badlands transported the sediment deposited on the channels during the previous summer and eventually that from preceding years.
