Influence of piping processes on the relief evolution. Bardenas Reales (Navarra, Spain)

Abstract

Piping processes are controlled by many interacting factors, such as dispersion index and sodium content, SAR and ESP, together with other important factors as cracking density, slope degree and climate. In the study area piping is linked to poor developed soils with high sodium contents which give raise to an intense regolith cracking that favours infiltration and finally piping. As the results show piping in this area can be separated in two different types depending on its genesis, one based on seepage processes, considered as a true type, and another due to tunnelling processes. From a distributional point of view piping is linked to two concrete situations: the massive intermediate levels of the intermediate Holocene filling sediments and the sediments deposited by gullies. In the tertiary materials, in general, it does not manage to develop. On Holocene materials pipes size and scale show a clear relationship among the level thickness, slope and hydraulic gradient, being the first one the principal bounding factor. Pipes developed on the lower laminated levels do not reach important depth due to the high number of discontinuities, generating centimetre-scale conduits that are always on duty to the drainage network. On gullies sediments piping are related to gullies margin evolution and headcut retreat. Pipes size and diameter are a direct function of gully dimensions and are inversely proportional to the proximity to gully scarp. Pipes are on a metric scale with a vertical pattern which development in depth is controlled by upper level thickness, since they are circumscribe to him.