Spatial and temporal patterns of soil erosion rates in an agricultural catchment, central Belgium

This paper presents results on the temporal and spatial variability of the erosional system in two adjacent cultivated catchments located in the Belgian Loam belt. Annual catchment erosion rates, calculated for the whole catchment area, range between 1 and 15 m3/ha · y. Mean annual catchment erosion rates calculated for a three year period, were 5.4 m3/ha · y and 8.2 m3/ha · y despite relatively low slope gradients. About 60 to 70% of the total soil loss due to rill and ephemeral gully erosion occurred in late spring and early summer. This is attributed to the higher frequency of high-intensity low-frequency storms falling on a very dry soil surface in late spring and early summer. The relative importance of ephemeral gully erosion is strongly influenced by the season: mean ratio of ephemeral gully erosion rates to rill erosion rates equals ca. 1.7 in winter and ca. 1.0 in summer. Ephemeral gully erosion in topographically defined flow paths is the dominant sediment source and represents 41% of the total soil loss. During the survey period, about 90% of the material eroded upstream was transported outside the catchment. As a result, villages situated downstream were severily damaged by flooding and major sedimentation events.