Water and sediment budgets unveiling contrasting hydro-sedimentary patterns in a mountainous Mediterranean catchment

Mountain regions have a key role in the generation of runoff, and in the production and transfer of sediments to fluvial networks, especially in Mediterranean catchments where these processes are affected by marked changes in climate and land use (i.e. global change). This paper presents the water and the sediment budgets of the Ribera Salada (224 km2), a meso-scale Mediterranean forested catchment located in the Southern Pyrenees. Field monitoring follows an integrated basins scheme (five nested sub-catchments), where hydrological and sediment transport data were collected continuously over a two-year period (2012–2013). Precipitation was obtained using radar images, which allowed the elaboration of rainfall maps used to characterize the spatial distribution of rainfall across multiple scales. Results indicate that the catchment is hydrologically divided in two areas which show contrasting fluvial regimes: the upper part of the catchment is considered wet and has a constant flow regime, supplying the majority of the water, while the lower part is drier, with ephemeral tributaries and water losses into the alluvial aquifer of the main river channel. In contrast to water yield, most of the suspended sediment load (i.e. 80%) is supplied by the driest part of the catchment where sediment availability was greater and where there is a greater connectivity between sediment sources and the channel network. The sediment yield of the whole catchment and the respective sub-catchments sits in the lower bounds of values reported for the Mediterranean region, indicating the generally low intensity of hydrological and geomorphic processes in the area. Once more the sediment budget approach matched to sound hydrological data proves efficient to characterize sediment dynamics in river basins, with special interest in areas such as the Mediterranean mountain catchments, where the effects of global change appear to be more acute.Authors acknowledge the support from the Economy and Knowledge Department of the Catalan Government, Spain through the Consolidated Fluvial Dynamics Research Group (2017 SGR 459), and the additional support from the CERCA Programme. This research was partly developed in the frame of the SCARCE Consolider Ingenio 2010 Project CSD2009-00065 (2009–2014) funded by the Spanish Ministry of Economy and Competitiveness, Spain. The second author was funded by a Ramón y Cajal Fellowship (RYC-2010-06264, Spanish Ministry of Economy and Competitiveness, Spain) during most of the research; he is now a Serra Húnter Fellow at the University of Lleida. Part of the instrumentation was funded by the project ‘Sediment Export from Large Semi-Arid Catchments: Measurements and Modelling’ (SESAM), funded by the Deutsche Forschungsgemeinschaft, Germany (DFG). Authors are especially indebted to David Estany for his invaluable assistance during fieldwork, and Chris Gibbins for a complete revision and discussion of the first draft of this manuscript