Impact mechanisms and morphological characteristics of Nam Pam debris flow - flash flood catchment

Abstract

Understanding the mechanisms and damages caused by debris flows and flash floods is crucial for proposing effective mitigation conterneasures. This study aims to clarify the impact mechanisms and morphological characteristics of a debris flow and flash flood event that occurred from the night of August 2, 2017 to the early morning of August 3, 2017, in Nam Pam commune, Muong La district, Son La province. The study involved field surveys and analysis of the morphological characteristics of the sub-catchments within the Nam Pam stream catchment. The morphological characteristics of the catchment area were analysed by quantifying the relationships between parameters such as area, slope, elevation, length, Melton coefficient… contributing to supplementing the database for identifying high-risk
catchment areas prone to debris flows. The 2017 flash flood event in the Nam Pam stream catchment was a multi-hazard phenomenon resulting from rainfallinduced geological transformations. The transformation process started from higher elevations, with widespread landslides caused by rainfall transforming into concentrated "debris flows" in the primary subcatchment channels, then transitioning into "debris flow-flash floods" in the secondary sub-catchments,
followed by "flash floods-debris flows" in the tertiary sub-catchments, and ultimately transforming into "flash floods" in the fourth-order catchment area.