Regional scale modeling of hillslope sediment delivery: a case study in the Ésera—Isábena watershed, central Spanish Pyrenees, with WATEM/SEDEM

Abstract

Soil erosion and sediment delivery to streams is an important environmental problem and a major concern for sustainable development. The spatial nature of soil erosion and sediment delivery, as well as the variety of possible soil conservation and sediment control measures, require an integrated approach to catchment management. A spatially-distributed soil erosion and sediment delivery model (WATEM/SEDEM) was applied to the watershed of the Barasona Reservoir (1504 km2; central Spanish Pyrenees), which is drained by the Ésera and Isábena rivers. Several input data layers with a 20 x 20 m resolution were derived using a GIS package comprising a digital terrain model (DTM), and stream network, land use, rainfall erosivity, soil erodibility and crop management factors. Validation of the model was based on the depositional history of the Barasona Reservoir using data on suspended sediment obtained over three years (May 2005 to May 2008) at the outlet of the Isábena River. This enabled estimation of the average annual sediment yield to the reservoir, as well as the relative contribution of each river. Almost 70% of the sediment yield to the reservoir was derived from the Ésera River, which coincided with the relative size of its sub-catchment. Large spatial variability in hillslope sediment delivery was found within the catchment, with major sediment sources being located in the lower part of the watershed (agricultural fields), and in the badlands on Eocene marls located in the middle part of the watershed (Pyrenean Inner Ranges), which are strongly eroded over convex hillsides with a moderately inclined slope.