Monitoring of flood and debris flow passing through a stream reach embedded with a step-pool system

Flood and debris flow frequently transpire in mountainous regions, leading to ground vibrations that can be detected by geophones. The quantitative analysis of these ground motion signals provides valuable seismology-based insights. This study centers on a previously unmonitored debris flow gully that incorporates an artificial step-pool system designed for debris flow mitigation. An integrated monitoring system was implemented, consisting of meteorological, hydrological and seismic sensors, to monitor flood and debris flow events. The recorded seismic signal was analyzed by means of short-time Fourier transform, and a bedload-induced model was utilized to compute the sediment flux. The results indicated that flood and debris flow can be distinguished by the short-term average/long-term average (STA/LTA) method, with thresholds of 30 and 20 for upstream and downstream stations, respectively. The sediment fluxes and transport rates passing through the monitoring stations were evaluated. Considering the topographic variation, the sediment source was identified. And the presence of step-pools mitigated the magnitudes of debris flow from upstream to downstream stations, leading to localized erosion within the downstream reach. The results offer valuable insights for monitoring debris flow and analyzing sediment movement influenced by bed structures such as step-pools.