Description:
<jats:p>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<jats:sup>−3</jats:sup> to 3.33 × 10<jats:sup>−3</jats:sup> m<jats:sup>2</jats:sup> s<jats:sup>−1</jats:sup>, and the sediment transport capacity (<jats:italic>T<jats:sub>c</jats:sub></jats:italic>) 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 <jats:italic>T<jats:sub>c</jats:sub></jats:italic>), and the detachment rate (<jats:italic>D<jats:sub>r</jats:sub></jats:italic>) under each combination of the slope and discharge was measured. <jats:italic>D<jats:sub>r</jats:sub></jats:italic> 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 (<jats:italic>D<jats:sub>c</jats:sub></jats:italic>) and <jats:italic>T<jats:sub>c</jats:sub></jats:italic> well (Nash–Sutcliffe efficiency coefficient (NSE) = 0.98 for <jats:italic>D<jats:sub>c</jats:sub></jats:italic>, and NSE = 0.99 for <jats:italic>T<jats:sub>c</jats:sub></jats:italic>). The detachment–transport coupling equation can adequately predict the <jats:italic>D<jats:sub>r</jats:sub></jats:italic> (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 <jats:italic>D<jats:sub>r</jats:sub></jats:italic> under <jats:italic>T<jats:sub>c</jats:sub></jats:italic> levels of 20% and 40% were higher than the measured values, while the predicted value under a <jats:italic>T<jats:sub>c</jats:sub></jats:italic> 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.</jats:p>