Application of artificial step-pools in natural hazard mitigation

The step-pool is a representative riverbed structure that is highly effective in increasing flow resistance and dissipating flow energy. Well-designed artificial step-pools can control channel incision, improve riverbed sta-bility, and further mitigate natural hazards. In this study, step-pools following the characteristics of natural step -pools in terms of their geomorphology and energy dissipation are designed and applied to mitigate channel incision and debris flow, in a small watershed where riverbed structures are poorly developed and landslides and massive debris flow have occurred frequently as a result of channel incision. The jamming ratio of the step-pools is mostly less than 6.0, and the SP values, i.e., the development degree of riverbed are over 0.1, and these values are increased significantly compared with the original values, guaranteeing the stability of the constructed steps. Field investigation indicated that the artificial step-pools experienced little adjustment and generally remained stable during the flood season. The constructed steps caused a decreasing trend in deposition downstream, and achieved the expected effects in natural hazard mitigation effects by reducing and transferring the debris flows to hyper-concentrated flows and eventually to normal flood flows. Therefore, the stable step-pools effectively suppressed massive sediment movements, with 69.3% of the loose sediment eroded from the water erosion zone being trapped in the step-pool reach, which promoted uplift of the channel bed. Numerical simulation of debris flows reveals that the maximum kinetic energy of debris flow was reduced by about 27 % with the artificial step -pools compared to the pre-construction condition. The scientific findings and practical applications concerning the use of artificial step-pools could provide guidance for natural hazard mitigation in mountainous areas at the small watershed scale.

Automated summary

This study designed and applied artificial step-pools that mimic the geomorphology and energy dissipation characteristics of natural step-pools to mitigate channel incision and debris flow. Field investigations showed that the artificial step-pools remained stable during the flood season. The constructed step-pools reduced sediment deposition downstream and effectively reduced the maximum kinetic energy of debris flow.