Effect of channel confluence on the dynamics of debris flow in the Niutang Gully

Debris flows are dangerous, rapid, and often observed in precipitous landslides comprising water-laden soil, rock, and debris. Moreover, under the influence of large-scale precipitation, the occurrence of debris-flow clusters may lead to confluence, altering their movement dynamics and the extent of their impact. Such events present a substantial risk to human life and safety, as well as causing severe damage to the ecological environment near the flow channels; however, the dynamic processes during debris flow confluence remain poorly understood. Here, we numerically simulated the flow process of debris flows based on observational data of the August 19–20, 2011 (“8.20”) debris flow in the Niutang Gully. Additionally, the investigation examined how the number of channels and the angles between channels at the confluence location affect the movement characteristics of post-confluence debris flow. The results indicated that upon the confluence of channelized debris flows, the velocity and deposition height of the debris flow vary with changes in the confluence angles. As the angle between the channels in the confluence area increases, so does the height of the sediment deposition, while the speed of the debris flow is reduced. Furthermore, the confluence angles affected the morphology of the debris flow deposition. As the confluence angle increased, so did the length of the debris-flow deposit fan, while the breadth was reduced. These findings show that the confluence has a substantial impact on the movement characteristics of debris flows, and this information may serve as a theoretical reference for debris-flow protection engineering.