Mechanisms and benefits of segmented eco-geotechnical measures for debris flow mitigation

Eco-geotechnical measures are increasingly recognized as holistic approaches to disaster mitigation. While the mechanisms underlying disaster mitigation for individual measures (ecological or geotechnical) are relatively well understood, the synergistic benefits and optimal layout of combined models remain unclear. This study proposes an eco-geotechnical model that integrates a segmented vegetation arrangement with comb-toothed dams for debris flow interception. Through field investigations and flume experiment, we delineated the optimal row and stem spacing of segmented vegetation. Additionally, we examined various combination models comprising vegetation filter strips and comb-toothed dams to elucidate their respective benefits and underlying mechanisms in debris flow interception. Results show that optimal interception occurs with tree filter strips at a stem spacing of 6 cm and row spacing of 8 cm and with shrub filter strips at a stem spacing of 3 cm and a row spacing of 4 cm. Moreover, equations were developed for flow velocity reduction and sediment interception, incorporating vegetation layout parameters (e.g., plant spacing, row spacing, number of rows), vegetation morphological parameters (e.g., diameter), and gully bed slope and roughness. Our comparative analysis underscores the superiority of the shrub-grass (dam) model in intercepting dilute debris flows, while the tree-shrub (dam) model excels in mitigating viscous debris flows by achieving notable reductions in flow rate, flow velocity, and sediment interception. Importantly, these findings provide a quantitative basis for optimizing vegetation layouts, advancing nature-based solutions and technologies for comprehensive disaster prevention and mitigation.