Amplification effect of transportation construction disturbances on disaster-forming risk of flash flood-debris flows in mountainous gullies: A case study of “8·21” disaster in Jinyang, Sichuan

Abstract

[Objective] Construction disturbances from projects such as transportation infrastructure in mountainous areas are often unavoidable and may increase the risk of flash flood-debris flows in the affected areas. Scientifically identifying and evaluating the impact of construction disturbances on the disaster-forming risk of flash flood-debris flows is conducive to preventing induced natural disasters. [Methods] The 2023 “8·21” flash flood-debris flow disaster in Jinyang, Sichuan was taken as a case study. Based on field investigations and remote sensing interpretation, the forms of construction disturbances were analyzed, and a scenario-based simulation comparison method was proposed to identify the amplification effect of construction disturbances on flash flood-debris flow risk. The risk amplification effect result ing from the superposition of construction material sources in this event was elucidated. [Results] The results showed that:(1) supplying short-range direct material sources and occupying flood discharge areas were the main forms through which construction disturbances affected the disaster-forming risk of flash flood-debris flows, respectively increasing the disaster-forming risk degree and the vulnerability of affected areas.(2) In the disaster occurring in Jinyang, Sichuan, the supply of construction-induced material sources caused the maximum burial depth at the disaster-forming cross-sections to increase by 2.65 m, which was the direct cause of the severe destruction of temporary construction housing.(3) The construction disturbances in this event caused the disaster-forming risk of the temporary housing to increase from a 50-year return period to a 20-year return period, significantly amplifying the disaster-forming risk of flash flood-debris flows. [Conclusion] The scenario-based simulation comparison method can effectively identify the amplification effect of construction disturbances on flash flood-debris flow risk. It emphasizes that during transportation construction in mountainous areas, the placement of temporary housing on the concave banks of gently widening river sections should be avoided. Reducing disturbances to bank slopes and enhancing bank slope erosion protection can significantly suppress the amplification effect of disturbances on the disaster-forming risk of flash flood-debris flows.

Keywords

flash flood-debris flow / disaster-forming risk / construction disturbance / numerical simulation / identification / construction material sources / rainfall / remote sensing