Feedback mechanism between gully landforms and sediment trapping efficiency in a check dam

Check dams have been used worldwide for a variety of purposes. With increasing age, check dams gradually lose their sediment trapping function via the continuous deposition of material carried by debris flows and flash floods, and eventually, check dams become unable to perform the designed mitigation function. In this paper, the sediment deposit evolution in a dam with multiple debris flow surges and its influence on the sediment trapping effect were investigated. The results showed that the debris flow deposition process can be divided into three phases: the backwater-controlled deposition phase, landform-controlled deposition phase, and quasi-equilibrium phase. The sediment trapping ratio of the check dam gradually decreased as the deposit volume increased and was linearly negatively correlated with the sediment deposition rate. Moreover, a mathematical model describing the negative feedback between deposit volume and sediment trapping ratio was established, and the physical meanings of the coefficients in the model and their empirical values were clarified. Furthermore, the deposit distribution, which satisfied the Weibull distribution in the longitudinal direction, was revealed. In the cross-sectional direction, the distribution of deposition gradually became uneven with increasing sediment filling rate.