Assessing the hillslope-channel contributions to the catchment sediment balance under land use and climate change

JPC Eekhout, A Jódar-Abellán, E Carrillo-López, C Boix-Fayos and J de Vente

July 24-25, 2024

ICCE, Eichstätt, Germany

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Abstract

Most soil erosion models simulate hillslope erosion processes, such as sheet and rill erosion. However, observations have shown that channel erosion processes become important at larger spatial scales, which are hardly ever considered in soil erosion impact assessments. Hence, to get a full understanding of the impacts of global change on the catchment-scale sediment balance, models are needed that combine hillslope soil erosion processes with channel morphodynamics. Here we present a modification to the SPHY-MMF model that includes a novel channel morphodynamics module, which determines erosion and deposition in rills and channels, besides sheet erosion that was previously implemented in the SPHY-MMF model. We applied the model to a Mediterranean study area in southeast Spain. The model was calibrated using observed check dam sediment yield data, which gave satisfactory results for check dams located in the channels. The model was subsequently applied under historical land use change and future climate change scenarios. The model simulations show that channel erosion contributes substantially (35%–40%) to the total sediment yield, highlighting the importance of accounting for channel erosion in catchment-scale sediment budget estimations. The land use change scenarios were applied in a smaller subcatchment, which is characterized by reforestation and check dam construction between 1956 and 2016. The results show an 80% decrease in sediment yield at the outlet, because of the implementation of these soil conservation measures. The results also show a slight increase of rill and channel erosion, which may be a response to the decrease in sediment input from the hillslopes. The climate change scenarios show that the different erosional processes (i.e. sheet, rill, channel) are projected to decrease or increase, depending on the projected change in annual and extreme precipitation. From this we conclude that interactions between different erosional and depositional processes should be considered when studying the impact of global change on the catchment-scale sediment balance. This will also allow policy makers to plan conservation measures more efficiently, by applying measures close to the sources with the highest contribution to the catchment-scale sediment yield, accounting for possible interactions with other erosion or deposition processes within the catchment.