The thesis works of Nataline Simon present a high potential of innovation and/or technology transfer. They focus on the « Development of active-Distributed Temperature Sensing (A-DTS) experiments to quantify groundwater flows: capabilities and limitations for characterizing groundwater-surface water interactions ».
Understanding groundwater and stream water interactions as integral components of a stream catchment continuum is crucial for efficient development and management of water resources. Particularly essential for the preservation of groundwater dependent ecosystems and riparian habitats, these interactions play a major role on physical, geochemical and biological processes occurring in the stream or in the hyporheic zone. More specifically, these exchanges control water quality affecting river ecohydrology and hydrochemistry, particularly during dry periods when groundwater is the principal contribution to stream discharge.
In this context, the aim of the PhD project was to develop and propose very innovative methods and tools for characterizing water exchanges occurring between streams and aquifers. The developed method consists in estimating through field measurements the water fluxes occurring within the sediments of streambeds. It relies on the use of the DTS technology (Distributed Temperature Sensing) that provides continuous temperature measurements through space and time along fiber optic cables at high spatial and temporal resolution. Fiber optic cables are deployed and buried in the sediments of a streambed. The cable is electrically heated through its steel armoring and the elevation in temperature, associated to the heat injection, is continuously monitored all along the heated section using the FO inside the cable. Without any flow, heat transfers occur through the porous media only by conduction and a gradual and continuous increase of temperature is therefore expected. If water flows through the porous medium, advection partly controls the thermal response by dissipating the heat produced by the heat source. The higher the water flow, the lower should be the temperature increase.
Although preliminary studies suggested the potential of the approach for characterizing water fluxes, Nataline went way further by proposing a full framework allowing the generalization of the application of the methods in the field to characterize flows in saturated porous media. Through the combination of a numerical model with laboratory experiments, she highly improved the understanding of the thermal processes controlling the temperature increase and fully validated two complementary and independent interpretation methods providing an estimate of both the thermal conductivity and the groundwater flux.
Experimental Setup near the Selune River (Normandy)
Once the method was validated, heat transport experiments were conducted within the streambed sediments of two different streams: in a first-order stream in Brittany, then in a large flowsystem located along an alluvial plain in Normandy. These applications demonstrated the relevance of using distributed methods to characterize the spatial complexity of stream exchanges.
PhD thesis: Nataline Simon, (2020) Développement des méthodes actives de mesures distribuées de température par fibre optique pour la quantification des écoulements souterrains : apports et limites pour la caractérisation des échanges nappe/rivière. Université de Rennes 1. tel-03101835v1
For more information :
Nataline Simon, Olivier Bour, Nicolas Lavenant, Gilles Porel, Benoît Nauleau et al. Numerical and experimental validation of the applicability of active‐DTS experiments to estimate thermal conductivity and groundwater flux in porous media. Water Resources Research, 2021, 57 (1), pp.e2020WR028078. ⟨10.1029/2020WR028078⟩
Nataline Simon, Olivier Bour, Nicolas Lavenant, Gilles Porel, Benoît Nauleau et al. A Comparison of Different Methods to Estimate the Effective Spatial Resolution of FO-DTS Measurements Achieved during Sandbox Experiments. Sensors, 2020, Distributed Optical Fiber Sensing, 20 (2), pp.Art. n°570. ⟨10.3390/s20020570⟩
Nataline Simon, Olivier Bour, Mikael Faucheux, Nicolas Lavenant, Hugo Le Lay et al. Combining passive- and active-DTS measurements to locate and quantify groundwater discharge into streams, Hydrol. Earth Syst. Sci. Discuss. [preprint], <10.5194/hess-2021-293>, in review, 2021.