Modelling lake-groundwater interactions in preparation of future SWOT mission: the case of the gravel pit lakes in the Seine River alluvial plain, France.

Gravel pit lakes created by sand and gravel mining are structural landscape elements in alluvial plains. As they create openings through the aquifer, they provide direct access to groundwater and make it possible for remote sensing to offer an integrated vision of water resources at the alluvial plain scale. Indeed the Surface Water and Ocean Topography (SWOT) satellite mission will soon map near weekly the surface water elevation of reservoirs with areal extent greater than 6 ha. Using the CNES large scale simulator, we evaluated the SWOT water level errors on gravel pits in La Bassée alluvial plain, in the middle reach of the Seine River (France). Despite their rather small size, the elevation accuracy over the artificial lakes should be centimetric. Using as input in-situ lake level measurements, SWOT-like outputs were generated. The full exploitation of these data requires a modelling tool for gravel pit lake simulation, which includes groundwater interaction. We also present the development of our lake module, imbedded in the CaWaQS platform, its validation using benchmark test problems and numerical experiments illustrating its performance in simulating gravel pit lake stage fluctuations.