Geodynamic processes on sandy slope gullies in central Spain field observations, methods and measurements in a singular system

Gullies developed on sandy lithologies are scarce and few studies have been reported on these landscapes. This paper presents an approach to study such singular landforms. The studied gullies appear on the slopes of a group of mesas and cuestas of Upper Cretaceous sediments located in the Northern piedmont of the Guadarrama Mountains, Spain. Landforms of these gullied areas were catalogued, characterized and quantified with reconnaissance methods, providing information about the most active geomorphic processes. These are being monitored in a 1.32 ha representative gullied catchment, the Barranca de los Pinos. In its high gradient slopes, where mass movements occur, high resolution topographical surveys are being carried out by Terrestrial Laser Scanning (TLS). On low gradient slopes, runoff and rain splash are being monitored in micro plots; and in the main channel, sediment transport and water discharge are being measured. This ensemble of methods, some of them novel, is providing patterns of sediment movement within the gully system, and a hypothesis of high activity rates has been confirmed. High gradient sand slopes without carbonate caprock erode fourfold compared to the capped slopes. In the low gradient slopes, those ungullied produce more runoff while exposed sands yield more sediment; sands covered by litter produce the least runoff and sediment. Notably, this catchment yields mainly bedload.