Erosion and sediment budget across scale: A case study in a catchment of the European loess belt

SummaryIn many cultivated areas of the loess belt in Northern Europe, loamy soils are particularly sensitive to runoff and erosion. Those processes may not be continuous within a catchment, and runoff and erosion responses to rainfall events differ depending on the study scale at which they are examined. Many of the underlying mechanisms of this scale effect are still unknown and/or not well described. The objective of this paper is to identify and quantify the scale effects on runoff and erosion, from the field scale to the catchment scale in the context of the Austreberthe catchment, located in Normandy, in an agricultural area of the loess belt. Based on extensive information compiled at the hillslope and the catchment scales, the runoff and erosion budgets are compared between both scales, showing a more important decreasing effect for erosion (95%) than for runoff (85%) when moving from the hillslope to the catchment scale. The reduction due to the scale change is linear for runoff but not for erosion, underlining the complexity of erosion processes. Comparison of these budgets between both scales shows a significant effect of the vegetation cover as an important connectivity parameter at the hillslope scale, but not at the catchment scale.The importance of the connectivity is also quantified when comparing runoff and erosion budgets between two states of the catchment connectivity: the connectivity without soil and water conservation measures and a modified connectivity (with soil and water conservation measures). This change of connectivity in the catchment was estimated to lead to a decrease in discharge and erosion rates of 50% and 90%, respectively.Finally, the sediment budget analysis from the field to the river basin scale shows that 80% of the mobilised sediments on the slopes are deposited before reaching the Austreberthe River. From the Austreberthe catchment (215 km2) to the Seine River Basin (more than 65,000 km2 the calculated reduction of the erosion rate is only 25%. In this context, the scale effect is more important on hillslopes, where there is not any permanent river channel and where connectivity depends on rainfall events and landscape organisation, than in catchments drained by perennial rivers.

► Scale in soil detachment and transport.
► Multi scale databases of runoff and erosion measurements.
► Predominance of hillslope connectivity compare to river connectivity.
► Sediment budget of the Austreberthe river.