Verification of the detachment-transport coupling relationship of rill erosion using colluvium material in steep nonerodible slopes.

Abstract

The detachment-transport coupling equation by Foster and Meyer is a classical equation that describes the relationship between detachment and transport. The equation quantifies the relationship between sediment loads and soil detachment rates, deepens the understanding of soil erosion and provides a reliable basis for the establishment of an erosion model. However, the applicability of this equation to slopes with gradients greater than 47% is limited. In this work, the detachment-transport coupling relationship is investigated using the colluvium material of Benggang. A nonerodible rill flume 4 m long and 0.12 m wide was adopted. The slope gradient ranged from 27% to 70%, the unit flow discharge ranged from 0.56 × 10-3 to 3.33 × 10-3 m2 s-1, and the sediment transport capacity (Tc ) was measured under each slope and discharge combination. The sediment was inputted into the flume according to the predetermined sediment addition rate (from 0% to 100% of Tc ), and the detachment rate (Dr ) under each combination of the slope and discharge was measured. Dr linearly decreased with increasing sediment loads, which is consistent with the detachment-transport coupling equation by Foster and Meyer. The linear equations can predict the detachment capacity (Dc ) and Tc well (Nash-Sutcliffe efficiency coefficient (NSE) = 0.98 for Dc , and NSE = 0.99 for Tc ). The detachment-transport coupling equation can adequately predict the Dr (NSE = 0.89). However, its applicability to slopes of <47% (NSE: 0.92-0.96) was greater than that to slopes of ≥47% (NSE: 0.81-0.89), and the predicted Dr under Tc levels of 20% and 40% were higher than the measured values, while the predicted value under a Tc level of 80% was lower than the measured value. In summary, the detachment-transport coupling equation by Foster and Meyer can accurately reflect the negative feedback relationship between detachments and transports along steep-slope fixed beds and is suitable for colluvial deposit research. The results provide a basis for the construction of steep-slope colluvial deposit erosion models. In the future, the study of the hydrodynamic characteristics of sediment transport processes should be strengthened to clarify the detachment-transport effect of flows through hydrodynamics.