Résumé
Research in karst hydrogeology is mainly focused on the study of spring’s functioning and disregards the larger scales as those of the karstic rivers, which are often the usual sources for water supply needs. At this large scale, catchments may have complex hydrological response because of strong surface/groundwater interactions, calling to the development of new methods to investigate stream water gains and losses from and to karst units. Therefore, the aim of this study is to understand better the hydrogeology of large karstic catchment using a routing hydrological model that quantifies lateral flows across stream network.The model used is the diffusive wave flood routing model able to simulate the dynamic of uniformly distributed lateral flows on river reach between two gauging stations. The application was conducted on the karstic catchment of the upper Loue River (1900 km²) in the French Jura Mountains during highest flood events for 30 years on hourly data.Simulations on four reaches show globally a high spatial variability of lateral gains and losses according to hydro-meteorological conditions. First, a model application on a losing reach allows quantifying the discharge losses which were interpreted as the localised recharge of a binary karst aquifer. Second, an application on gaining reaches shows that the spatial variability of karst contributions to the stream reflects the main groundwater drainage axes identified by spring’s location and artificial tracer tests. Finally, the karst contribution decreases downstream where surface runoff is favoured locally on marly areas.Our results suggest that a distributed representation of surface/groundwater interactions can improve the understanding of how the stream signal is controlled by karst units at large scale. It gives finally insights on the future development of a distributed modelling approach of karstic catchments.