Continental hydrosystem modelling: the concept of nested stream–aquifer interfaces

Abstract. Recent developments in hydrological modelling are based on a view of the interface being a single continuum through which water flows. These coupled hydrological-hydrogeological models, emphasising the importance of the stream–aquifer interface, are more and more used in hydrological sciences for pluri-disciplinary studies aiming at investigating environmental issues. This notion of a single continuum, which is accepted by the hydrological modellers, originates in the historical modelling of hydrosystems based on the hypothesis of a homogeneous media that led to the Darcy law. There is then a need to first bridge the gap between hydrological and eco-hydrological views of the stream–aquifer interfaces, and, secondly, to rationalise the modelling of stream–aquifer interface within a consistent framework that fully takes into account the multi-dimensionality of the stream–aquifer interfaces. We first define the concept of nested stream–aquifer interfaces as a key transitional component of continental hydrosystem. Based on a literature review, we then demonstrate the usefulness of the concept for the multi-dimensional study of the stream–aquifer interface, with a special emphasis on the stream network, which is identified as the key component for scaling hydrological processes occurring at the interface. Finally we focus on the stream–aquifer interface modelling at different scales, with up-to-date methodologies and give some guidances for the multi-dimensional modelling of the interface using the innovative methodology MIM (Measurements-Interpolation-Modelling), which is graphically developed, scaling in space the three pools of methods needed to fully understand stream–aquifer interfaces at various scales. The outcome of MIM is the localisation in space of the stream–aquifer interface types that can be studied by a given approach. The efficiency of the method is demonstrated with two approaches from the local (~1 m) to the continental (<10 M km2) scale.