Nature-based solutions (NbS) and soil bioengineering techniques have gained considerable attention due to their relevant hydrological functions and ability to mitigate slope instability. Live pole drains (LPD), a lesser-known NbS, have traditionally been deployed on slopes to drain the excess surface water and regulate the soil's water budget, making it a suitable technique for stormwater management and landslide prevention. However, neither the LPD performance as a plant-based drainage system nor its potential to regulate the soil-water budget through hydrological processes have been thoroughly studied. This paper presents a novel pilot, lab-based approach for testing the hydrological performance of LPD under different soil hydrological conditions. We built three different treatments and investigated their hydrological performance under multiple storm events. We explored how LPD regulate the soil-water budget by partitioning the water inputs (i.e., rainfall precipitation) into water outputs (i.e., surface runoff, subsurface flow, and percolation). The study revealed that LPD can effectively manage stormwater by draining excess runoff and buffering water in the soil, outperforming fallow soil. Subsurface flow and percolation were significantly higher under LPD treatments when compared to fallow ground, suggesting that the presence of an enhanced structure in the soil results in high soil hydrological performance. The presence of a secondary species with the LPD showed a more efficient hydrological performance than an LPD alone, which aligns with the current implementation of NbS fostering biodiversity. Antecedent soil moisture impacted the hydrological performance of LPD by altering the relative infiltration capacity of the soil and by potentially modifying the availability of channels for preferential flow. Our findings provide a sound basis for future research to improve our understanding of the hydrological performance of LPD for slope instability mitigation and encourage their reproduction and upscaling.

Climate change causes an increase of precipitation intensity and frequency, which leads to an increased amount of landslide occurrences. Therefore, there is an urgent need for prevention measures. The risk of landslide occurrence can be mitigated by decreasing the pore water pressure in a hillslope, e.g. by drainage from the subsurface. The implementation of Nature Based Solutions (NBS) is advantageous, as these are not disruptive for the hillslope ecosystem. A Live Pole Drain (LPD) is a type of NBS which is inexpensive and can be installed at remote locations. However, its effect on hillslope hydrology has not been studied before.

In this study, fieldwork at an Open Air Lab, a laboratory experiment with miniature LPDs and the development of a conceptual model were used to characterise the hydrological behaviour of a slope in which a LPD is installed. After comparison of this hydrological behaviour to that of a slope with bare soil, it was found that a LPD facilitates rapid infiltration and drainage of precipitation and subsurface water. Furthermore, runoff volumes decrease after installation of a LPD and this effect is enhanced through plant development. Vegetation also contributes to the decrease of the stored volume of water in the subsurface through evapotranspiration. An increase of the design aspects diameter and macropore fraction of the LPD increases its drainage capacity. This study resulted in a first version of a numerical model to quantify the hydrological processes in a hillslope with LPD and the confirmation of the expected effect of drainage through preferential flow by a LPD.