A new method to compute the groundwater recharge for the study of rainfall-triggered deep-seated landslides. Application to the Séchilienne unstable slope (western Alps)

Abstract

Abstract. Pore water pressure built-up by recharge of underground hydrosystems is one of the main triggering factors of deep-seated landslides. Groundwater recharge, which is the contribution of the precipitation to the recharge of the saturated zone, is a significant parameter. However, in landslide studies, methods and recharge area parameters used to determine the groundwater recharge amount are rarely detailed. Currently, no turnkey method has been proposed to simply and accurately estimate the groundwater recharge. In this study, the groundwater recharge is estimated with a soil–water balance based on characterization of evapotranspiration, soil available water capacity and runoff. Although evapotranspiration estimation is a data-demanding method, many landslide sites have limited meteorological datasets. A workflow method is developed to compute daily groundwater recharge. The method requires only temperature and precipitation as inputs. Soil available water capacity and runoff quantities are determined from field observations and spatial datasets using a spatial composite approach before being refined with a sensitivity analysis. The proposed method is developed to be as versatile as possible in order to be readily applied to other landslide sites, and to be sufficiently simple to be used by any specialist who intends to characterise the relationship between rainfall and landslide displacements. Moreover, this method can be applied to any other parameters, as long as these parameters have a relationship with groundwater recharge. This study demonstrates that, for the Séchilienne landslide, the performance of the correlation between rainfall and displacement is significantly improved with groundwater recharge compared to results obtained with precipitation data.