Characterization of coarse-grained sediment supply for the assessment of soil erosion in mountainous areas. Application to the Upper Llobregat River Basin (Pyrenees, Spain)

In the scope of soil erosion modeling few attempts have been made to assess the coarse-grained sediments at steep slopes. The current approach results in a lack of correspondence in mountain watersheds because most models perform validation for different scales, topography, and land use, especially in the agricultural field. Available models normally prioritize the estimation of fine sediment in the field while the contribution of course-grained sediment is simplified or even neglected, especially in areas that require an analysis of hillslope failure events. 

Herein, we selected the Upper Llobregat River Basin (Pre-Pyrenees, Spain) as a study area and focus on the 1982 rainstorm, which triggered more than 1000 mass movements. The present investigation aims to allow an assessment of sediment production that focuses on the characterization of coarse sediment source areas from a mountain range.

The methodology includes analysis through geomatic methods, field surveys, and historic landslide inventories, followed by an index connectivity calculation to main rivers, morphometric parameters, and triggering factors. Preliminary results of this ongoing study confirm the importance of hillslope processes for the assessment of the sediment budget in mountainous areas. The outcomes will be incorporated into a modular sediment-budget model, which will be calibrated in our study area and tested in other watersheds in the Pyrenees. In addition, the impact of future changes (climate and land use) will be analyzed since extreme weather scenarios strongly affect both the production and transport of sediment in mountainous areas.