Geomorphic dynamics of gullies developed in sandy slopes of Central Spain

摘要

Gullies developed on sandy lithologies are scarce. Such landforms have developed in the sandy deposits of the Cretaceous ‘Utrillas’ facies within the Segovia province of Central Spain. They appear at the slopes of a group of mesas and cuestas located at the edge of the northern piedmont of the Guadarrama Mountains of the Spanish Central System. The activity of the different geomorphic processes acting in these gullies, as well as their connectivity, are being characterized and quantified. This study was preceded by reconnaissance methods, whereas presently technologically advanced and more accurate techniques are being utilized. The new methods are applied in an experimental catchment (1.26 ha). They include: i) an automatic Reid-type (formerly termed Birkbeck) slot bedload sampler for continuous monitoring of bedload flux and for continuous sampling of bedload; siphons for sampling the suspended load; and a Parshall flume to monitor water discharge. Jointly, these instruments allow to study the fluvial dynamics at the catchment mouth; ii) topographic surveys undertaken by a Terrestrial Laser Scanner (TLS) to quantify the activity of gravitational, overland flow and fluvial processes in different sediment source areas within the gully basin; iii) micro runoff and erosion plots to monitor the infiltration and erosive response of different Hydrologic Response Units (HRU) comprising the interior of the catchment. This ensemble of novel methods has started providing patterns of sediment movement within the gully system.