Linear scaling of precipitation-driven soil erosion in laboratory flumes

The proportionality between raindrop-driven soil erosion delivery and area of soil exposed to raindrops under a uniform precipitation rate was investigated in terms of individual size classes using laboratory flume experiments. In particular, we examined the dependence of soil erosion on the area exposed to raindrop detachment. Twelve experiments were performed on the same laboratory flume, filled with the same soil. The experiments entailed different (constant) precipitation rates (28 and 74 mm/h, 2-5 h duration) and various fractions of exposed surface (20, 30, and 40%, created using rock fragment cover). In addition, different initial soil conditions (dry hand-cultivated, wet sealed-compacted and dry compacted) were considered. The discharge rates and the sediment concentrations of seven individual size classes (< 2, 2-20, 20-50, 50-100, 100-315, 315-1000 and > 1000 µm) were measured at the flume exit. Results showed that the proportionality of soil erosion to the area exposed appears to always hold at steady state independently of the initial conditions and rainfall intensity. Across all experiments the data indicate that this proportionality holds approximately during entire erosive events and for all individual size classes. However, the proportionality for short times is less clear for the larger size classes as the data show that for these classes the erosion was sensitive to the soil’s antecedent conditions and further influenced by additional factors such as surface cohesion, surface compaction and soil moisture content.