Quantification of Rill Erosion Development in Marl Soils of Zanjanroud Watershed in North west of Zanjan, Iran

Soil erosion prediction models are of great significance for soil and water conservation management. Rill erosion is the most important component of hillslope soil erosion processes. Therefore، predicting hillslope erosion requires that rill erosion is well understood and predictable. The study was conducted to empirical quantification of rill development in the hillslopes. Rill characteristics consist of width، depth، cross section area، length، volume and soil loss، density of the rills and soil erosion rate along with slope characteristics (steepness and length) and soil properties were determined in 27 rills occurred on 9 hillslopes in marl formations of the Zanjanroud watershed، north west of Zanjan، Iran. All rill characteristics except the length showed significant correlation with both slope steepness and some soil properties including particle size distribution، sodium adsorption ratio، aggregate stability and saturated hydraulic conductivity. Rill depth as compared to other rill characteristics was reliably quantified in the hillslopes. This parameter had the highest relationship with slope steepness and saturated hydraulic conductivity (R2= 0. 67، p< 0. 001). Rill erosion rate contrary to the slope characteristics significantly related to clay content (R2= 0. 56). This result revealed that in order to develop a model to predict rill erosion، it is vital that investigate all hillslope characteristics a long with soil properties in the watershed surface.