Soil erosion resistance effects on rill and gully initiation points and dimensionsgully initiation points and dimensions

Recent research has indicated the large spatial and temporal variation in soil erosion resistance against concentrated fl ow (SER). This study analyzes this variability in relation to rill and gully initiation locations on slopes and the downslope eroded volumes. The soil erodibility (Kc) and critical fl ow shear stress (τcr), were estimated from topsoil properties and correlated to eroded rill and gully volumes and their initiation points on slopes in the Belgian loess belt. Therefore, concentrated fl ow paths and topsoil properties were measured in their vicinity. The results show that rill and gully initiation points, and hence the lengths of concentrated fl ow paths, depend on τcr, which is controlled by soil surface conditions and can be predicted from saturated soil shear strength. Soil erosion control measures that increase soil shear strength (e.g. thalweg compaction), can therefore decrease rill and gully lengths. Once a rill or an ephemeral gully is initiated, its cross-section was found to depend on Kc, which can be estimated from the soil water content, dry bulk density, and the dry density of roots and crop residues incorporated in the topsoil. 74% of the variation in the channel cross-sectional area measured in the study area could be predicted from the combined effect of fl ow intensity and these three soil properties, whereas fl ow intensity alone could only account for 31% of the variation. Soil conservation measures affecting one of the soil properties that control Kc (e.g. double drilling of the thalweg, conservation tillage) can therefore decrease the cross-sections of the concentrated fl ow paths. These fi ndings also indicate that rill and gully initiation points are not only topographically controlled but also depend on the SER, which in turn determines the dimensions of these concentrated fl ow paths. Hence, knowledge of the variability in SER is indispensable.status: publishe