Assessment of soil redistribution at catchment scale by coupling a soil erosion model and a sediment connectivity index (central spanish pre-pyrenees)

Abstract

The study and quantification of soil redistribution is a complex and difficult task and even a non-solved question at catchment scale both in field and numerical simulation studies. In this study we tackle this topic by coupling two different predicting models and a sound field-based dataset to assess the potential soil redistribution in a Mediterranean rain-fed agricultural and mountainous catchment (La Reina gully catchment, Cinco Villas region, NE Spain): the enhanced Modified-RMMF-2014 version of the “Modified Revised Morgan, Morgan and Finney” model (Morgan, 2001; López-Vicente and Navas, 2010) of soil erosion and the IC (Index of Connectivity; Borselli et al., 2008) model of sediment connectivity. In a cereal experimental plot (1.9 ha; 1 x 1 m of cell size), located in the lowlands of the La Reina gully catchment, we firstly ran the IC model under six different scenarios of runoff pathways and results were compared with field observations of soil redistribution. The best performance was obtained with the IC model when the map of geomorphic features (rills, ephemeral gullies and fan deposits) was used in the simulation. Predicted rates of both models were correlated at 613 control points and three areas where identified at the plot: erosive-, stable- and depositional- prone areas, affecting 30%, 22% and 48% of the soil surface, respectively. The average erosion rates in each area were 3.3, 1.5 and 1.1 Mg ha-1 yr-1 with standard deviation values of 20.3, 19.0 and 8.3 Mg ha-1 yr-1. Then, the IC model was run at La Reina gully catchment (231 ha; 5 x 5 m) and the IC values were analysed following the first approach. Stable areas and those mainly affected by processes of soil loss and deposition were identified. Results showed clear differences in the index of connectivity along the catchment though the extension of the areas with predominant processes of soil loss was under predicted (11% of the catchment area). Further research should be focused on the adjustment of the IC model to catchment scale. Our approach offers a simple and alternative method to assess spatially distributed processes of soil redistribution at catchment scale that can be of interest in ungauged catchments where calibration task of numerical models is difficult to be done.