Caracterización granulométrica del lecho móvil de un río de gravas efímero: Aplicación a un tramo de la riera de Les Arenes

Abstract

More than 676 kg were collected during a sediment survey campaign in the ephemeral gravel-bed stream of Les Arenes, NE Spain. Samples were taken in a selected reach distinguishing bed surface and the material beneath it or subsurface. Two different methods were used for sampling the surface (areal sample), and the subsurface (volumetric sample after clear the surface). Both samples were compared using the formal conversion of Kellerhals and Bray (1971). The results obtained, after applied the formal conversion and a lower truncation of 8 mm, permits to classify Les Arenes as a gravel-bed stream with a median surface diameter (D 50 sup) of 13 mm and a median subsurface diameter of 17 mm. The sediment survey campaign has allowed to demonstrate the lack of a surface or armouring layer coarser than the material underneath it. As a consequence of this, annual floods can move easily the median size of the bed, as opposite to what happen in perennial streams with a gravel-bed. In this paper, some practices are recommended to get representative samples of satisfactory precision for sampling a gravel-bed stream. And it shows how useful could be a correct sampling, in a selected reach, when the objective is the study of present fluvial processes.