Decoding Debris Flow Behavior: Simplified Insights into Entrainment and Deposition Dynamics

Abstract

Entrainment in debris flows is essential for comprehending the development of runout deposits. This research examines debris flow dynamics via 16 flume-based experiments with differing water content (w/c). Results indicate that shear forces predominantly facilitate entrainment, reaching their maximum at the transition from fixed to erodible beds. Entrainment did not occur below 24% water content, with peak entrainment seen at 50%. Elevated water content augmented erosion rates and runout distances, highlighting the significance of fluid composition in debris flow dynamics. Entrainment affected deposit morphology, resulting in broader, flatter deposits with poorly sorted particles akin to natural debris flows. A smartphone-based sensor technique was employed to assess deposit characteristics, providing an effective substitute for conventional 3D scanning. Validation via dimensionless numbers, such as Bagnold and Froude, confirmed the reliability of the results. This research enhances comprehension of debris flow dynamics and presents an economical experimental methodology. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2026.