Eco-hydrological characterisation of live pole drains (LPDs) for slope drainage and stability

Live pole drain (LPD) is an innovative, plant-based, drainage system designed to drain surface water, regulate the soil water budget, and facilitate ecological succession and landscape restoration in sloped areas. The system is constructed by placing tied cylindrical bundles of live woody cuttings capable of re-sprouting into a shallow trench along the slope. This design allows moderate surface runoff and seepage fluxes to infiltrate, conveying higher water flows along the fascine, thereby improving slope drainage and stability and preventing further soil erosion. Despite its practical applications, the overall eco-hydrological performance of LPD remains poorly researched and understood. This study aims to evaluate LPD's subsurface lateral drainage capacity and assess the impacts of soil-plant-atmosphere interactions on its water mass balance. To achieve this, we created two experimental setups at different scales to gain insights into the overall eco-hydrological performance of LPDs as opposed to fallow soil (i.e. control). At the micro-scale, we built a pilot laboratory experiment to measure subsurface lateral drainage flow rates and their distribution along the bundles of live cuttings and roots under controlled environmental conditions. At the mesoscale, we constructed an LPD on an artificial slope in an open-air lab (OAL) to investigate how plant development and seasonal changes influence the water mass balance of the system. Through both experimental setups, we observed the effect of LPDs on subsurface lateral drainage performance and soil-water mass balance compared to fallow soil. In the micro-scale experiment, root development positively impacted subsurface lateral drainage flow over time by increasing the flow cross-sectional area with respect to the control. At the plot scale, plant development and seasonality positively affected the partitioning of water inputs (i.e. precipitation) into water outputs (i.e. subsurface flow, percolation and evapotranspiration) within the water mass balance by increasing the removal of excess water when compared to fallow soil. This research will establish a solid foundation for future studies aimed at deepening our understanding of the eco-hydrological performance of LPDs at the plot scale, as well as supporting their design, replication, and scalability for effective slope drainage and stability.