Regional scale modeling of hillslope sediment delivery: A case study in the Barasona Reservoir watershed (Spain) using WATEM/SEDEM

Soil erosion and sediment delivery to streams are important environmental problems and major concerns in sustainable development. In recent years several tools have been proposed for assessing the delivery of sediment from hillslopes to stream networks, but there are still few examples of their application to large basins, and studies include a discussion of calibration and validation issues. In this study a spatially distributed soil erosion and sediment delivery model (WATEM/SEDEM) was applied to the watershed of the Barasona Reservoir (1504 km 2, Central Spanish Pyrenees), which is drained by the Ésera and Isábena Rivers. Model calibration and validation was based on the depositional history of the Barasona Reservoir and suspended sediment records over 3 years (May 2005–May 2008) at the outlet of the Isábena River. Despite interannual differences in precipitation and runoff, it was possible to establish an optimum value (7–23) for the ktc parameter. This enabled estimation of the long-term average annual sediment yield to the reservoir, as well as the relative contribution of each river. Large spatial variability in hillslope sediment delivery was found, and the major sediment sources were in the lower part of the watershed (agricultural fields) and in the badlands developed on Eocene marls in the middle part of the watershed (Pyrenean Inner Ranges). The relative importance of sediment source areas was assessed in relation to land use, and the relationship between the sediment delivery ratio and the catchment area was studied as a function of the geomorphological units. For the moment WATEM/SEDEM remains mainly as a researcher’s tool, until either the problem of the scarcity of soil erosion data or the need for calibration of the transport parameters will be solved.