Understanding Flash Floods in Hilly Tropical Watersheds: A Trigger Factor Analysis

Abstract

Flash floods are catastrophic phenomena known for their rapid and unpredictable occurrence. They frequently display precursory indicators, which, when comprehensively studied, serve as vital clues for effectively anticipating and preparing for these events, thus reducing their adverse effects. This study aimed to investigate the key trigger factors contributing to a flash flood event in the upper Ciliwung Watershed in January 2021. Data collection involved various parameters, including morphology, precipitation patterns, land use, hydrological characteristics, and soil conditions collected from the affected area. These data were subsequently analyzed using geospatial methods and enriched with information from local community members. The analysis found multiple contributing factors to flash floods, including high soil moisture content due to prolonged precipitation, geological characteristics, and steep topography. The local community recognized landslides, creating a natural dam about a month before the flash flood. Unfortunately, inadequate measures were taken to address the flood due to limited understanding and resources. The heavy rainfall before the flash flood put immense pressure on the natural dam, causing it to fail and carry debris downstream. The steep banks of the surrounding river worsened the situation. The study’s findings can provide valuable insights for local authorities, leading to better resource allocation.