Evolution of sediment-trapping effectiveness of check dams under multiple debris flows: an experimental study

Check dams are widely used for debris flow disaster mitigation, but their sediment-trapping effectiveness diminishes with multiple debris flow events. Exploring the evolution of the sediment-trapping ratio is crucial for planning check dam maintenance. This study uses physical model experiments to investigate how dam openings and sediment concentration (C v) affect this evolution. Results show that the sediment-trapping process of slit dams involves two phases: a slit-blocking controlled phase where the sediment-trapping ratio slightly increases, and a reservoir-filling controlled phase where it gradually decreases. The transition between these two phases occurs when the reservoir-filling ratio reaches 1.0–2.0. For solid-body dams, the slit-blocking phase is absent, and the sediment-trapping effectiveness is mainly controlled by the reservoir-filling state. The sediment-trapping ratio shows a linear negative correlation with the reservoir-filling ratio, and the correlation strengthens with increasing C v. Additionally, under the combined influence of debris flow dynamics (flow depth and Froude number) and rheological properties of the deposited sediment (excess pore water pressure dissipation), the average sediment-trapping ratio first increases then decreases with C v, peaking around C v = 0.3. Finally, we propose a conceptual model for the evolution of the sediment-trapping ratio under various check dam opening conditions.