Peak discharge amplication of debris flows in colluvial channels with varying cross-sections

Debris flows can significantly amplify both discharge and destructive potential as they flow over a colluvial channel with non-uniform cross-sections. However, the mechanisms driving this growth remain largely unclear. In this study, we examined the influence of channel narrowing or widening on debris flow dynamics through in-situ investigations following the debris flow events in Western China, specifically in Zhouqu in 2010 and Heixiluo in 2020. By introducing two dimensionless parameters, namely the discharge amplification factor and channel narrowness, we found a significant correlation between peak discharges of the debris flows and channel widths. When the channel narrows, the increase in flow velocity leads to flow amplification, intensifying the erosive force of the debris flow and causing more severe localized failure of the bed sediments. In contrast, when the channel widens, fluid dispersion results in a decrease in flow velocity, reducing the overall scale and destructive power of the debris flow. Based on experimental measurements, an exponential relationship between the flow amplification factor and channel narrowness was determined using regression analysis. This research may aid in comprehending the dynamics of debris flow and in the evaluation and mitigation of associated disasters.