Thesis Defence // Hanifa Bader

In agricultural landscapes, hedgerows do more than simply mark field boundaries: they can also alter subsurface water pathways. This thesis investigates the role of a hedgerow located in the Yzeron catchment, near Lyon, by instrumenting the site to compare water dynamics in the unsaturated zone beneath the hedgerow with those beneath the adjacent grasslands. Field measurements, numerical simulations, and a geophysical subsurface imaging method, electrical resistivity tomography, were used to monitor water infiltration following rainfall events and soil drying during the dry season. The results show that, in summer, the soil dries out more strongly and to greater depths beneath the hedgerow, whereas during wet periods, water can infiltrate and remain at greater depths beneath it. However, measurement campaigns conducted on other hedgerows within the catchment show that their hydrological functioning varies considerably from one site to another and according to subsurface characteristics. These findings therefore demonstrate that hedgerows influence water fluxes, but that their role strongly depends on the local context.