Flow-driven soil erosion processes in a calcareous semiarid soil: Rill length and flow rate impacts

Understanding the dynamic mechanisms of rill erosion is vital for accurately modeling of soil erosion. In this research, rill erosion was experimentally studied using different rill lengths. A flume, 11 m long and 0.2 m wide adjusted to 3% slope, was used for constructing rectangular rills of 0.05 m width and six different lengths (1 to 12 m). The experiments were carried out on a clayey calcareous soil from a semiarid region under two flow rates of QL = 0.025 and QH = 0.045 L s-1. Temporal sediment concentrations (C) were measured at the rill outlet for 40 min and the sediment size distribution (PSD) was recorded twice during each test. The common decreasing trend of C was affected by both flow rate and rill length. The formation of head-cuts along the bed of long rills was an important erosion process affecting C and PSD. The compiled data were used to determine the expo-nential models' parameters of both C and soil detachment rate based on the steady, unsteady, and event-average values. While, the equilibrium sediment transport occurred by increasing rill length beyond 7 m under QL, the tested rills under QH were not sufficiently long for the flow to reach its maximum transport capacity at the gentle slope used and for the calcareous soil tested. Based on the sediment PSD, the selective transport of coarse par-ticles was evidenced. Selectivity transport was affected by rill length reached its maximum at the rill length of 7 m.The findings provides better understanding of rill erosion processes for calcareous soils on gentle slopes in semiarid regions. Further research is needed for better understanding of the rill erosion processes on short gentle slopes to provide experimentally supports for the existing theoretical concepts of rill erosion models.