Experimental Assessment of Combined SABO Dam and Drainage System for Debris Flow Mitigation

Debris flows are rapid, high-energy mixtures of water and sediments that pose a severe threat to mountainous regions, often occurring with little warning and causing substantial loss of life and infrastructure damage. The design of effective structural countermeasures is therefore essential to mitigate their destructive potential. Open-type SABO dams are widely adopted to reduce the impact of stony debris flows by intercepting coarse material, while drainage systems enhance energy dissipation by removing part of the water content from the flowing mixture. This study investigates the novel approach of combining open-type SABO dams with drainage systems to enhance debris flow mitigation.

The complex multiphase physics governing debris flows severely limit the accurate reproduction of such events in both numerical simulations and laboratory experiments (Iverson, 1997), complicating the assessment and optimization of countermeasure performance. Although scaling effects introduce unavoidable uncertainty when scaling laboratory results to real-world environments, physical modelling remains a valuable tool for systematically testing alternative design configurations and identifying governing mechanisms relevant to preliminary engineering applications.

A total of 145 small-scale laboratory tests have been conducted, varying triggering discharges, channel slopes, SABO dam configurations (number and spacing of steel trestles), and drainage conditions. Starting from the framework proposed at EGU 2019 by Salandin and Lanzoni, the present study investigated two triggering discharges and two channel slopes, by including a SABO dam of varying numbers of steel trestles with different spacings between them, and multiple drainage configurations, allowing controlled variation of the degree of dewatering of the debris flow body. The spatio-temporal evolution of the sediment–water mixture surface was monitored using four ultrasonic sensors, water level was measured by a submersible pressure transducer, and debris-flow mass was quantified using a load cell.

The SABO dam efficiency is assessed in terms of energy dissipation, inferred from temporal changes in debris deceleration over time and from accumulation height upstream of the combined system. Results demonstrate that adding a drainage system significantly enhances the SABO dam energy dissipation capacity. This integration allows for larger trestle spacing while maintaining effective debris flow control. Moreover, under both drained and undrained conditions, our findings suggest optimal trestle openings that differ from current literature recommendations, highlighting the potential of integrated SABO–drainage systems to improve debris flow mitigation strategies.