This seminar is part of the Tuesday Seminar Series organized by the Center for Hydrogeology and Geothermics (CHYN) at the University of Neuchâtel. We are pleased to welcome Dr. Sarah Leray from the Université de Montpellier, who will discuss groundwater–surface water interactions and their role in shaping streamflow recession dynamics.

Abstract
Groundwater-surface water interaction through seepage faces occurs when the groundwater table intersects the land surface as saturation excess. This study uses a coupled hydrological model, interpreted in the framework of solutions to the Boussinesq equation, to explore how partitioning of surface and subsurface flow shapes recession. Analysing seepage in draining homogeneous hillslopes across topographical settings, we show that seepage flux is primarily governed by topographical features and occurs only in concave terrains, with more sustained seepage at higher concavity and aquifer thickness. However, seepage recession rates are driven by temporal changes in seepage length and affect only the early and middle stages of recession, thereby reducing the classic kinematic-wave behaviour observed on sloping hillslopes and dampening recession non-linearity in the middle stages. This study offers a new interpretation of recession dynamics through a quantitative link between recession nonlinearity and seepage length, providing a physical basis for predicting streamflow recessions.