03 Jun 2021

03 Jun 2021

Review status: this preprint is currently under review for the journal HESS.

Combining passive- and active-DTS measurements to locate and quantify groundwater discharge into streams

Nataline Simon1, Olivier Bour1, Mikaël Faucheux2, Nicolas Lavenant1, Hugo Le Lay2, Ophélie Fovet2, Zahra Thomas2, and Laurent Longuevergne1 Nataline Simon et al.
  • 1Univ Rennes, CNRS, Géosciences Rennes, UMR 6118, 35000 Rennes, France
  • 2UMR SAS, INRAE, Institut Agro, Rennes, France

Abstract. FO-DTS (Fiber Optic Distributed Temperature Sensing) technology has been widely developed to quantify exchanges between groundwater and surface water during the last decade. In this study, we propose, for the first time, to combine long-term passive-DTS measurements and active-DTS measurements in order to highlight their respective potential to locate and quantify groundwater discharge into streams. On the one hand, passive-DTS measurements consist in monitoring natural temperature fluctuations to detect and localize groundwater inflows and characterize the temporal pattern of exchanges. Although easy to set up, the quantification of fluxes with this approach often remains difficult since it relies on energy balance models or on the coupling of distributed temperature measurements with additional punctual measurements. On the other hand, active-DTS methods, recently developed in hydrogeology, consist in continuously monitoring temperature changes induced by a heat source along a FO cable. Recent developments showed that this approach, although more complex to set up than passive-DTS measurements, can address the challenge of quantifying groundwater fluxes and their spatial distribution. Yet it has almost never been conducted in streambed sediments. In this study, both methods are combined by deploying FO cables in the streambed sediments of a first- and second-order stream within a small agricultural watershed. A numerical model is used to interpret passive-DTS measurements and highlight the temporal and spatial dynamic of groundwater discharge over the annual hydrological cycle. We underline the difficulties and the limitations of deploying a single FO cable to investigate groundwater discharge and show the impact of uncertainty on sediments thermal properties on the quantification of groundwater inflows. On the opposite, the active-DTS experiment allows estimating the spatial distribution of both the thermal conductivity and the groundwater flux at high resolution with very low uncertainties all along the heated section of FO cable. Our results highlight the added values of conducting active-DTS experiments, eventually combined with passive-DTS measurements, to fully investigate and characterize patterns of groundwater-stream water exchanges at the stream scale. The combination of both methods allows discussing the impact of topography and hydraulic conductivity variations on the variability of groundwater inflows in headwater catchments.

Nataline Simon et al.

Status: open (until 29 Jul 2021)

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Nataline Simon et al.


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Short summary
Groundwater and stream water interactions play a major role for the preservation of stream ecosystems. Two complementary methods, both based on the use of the DTS (Distributed Temperature Sensing) technology were applied in a headwater catchment. Measurements allowed characterizing the spatial and temporal patterns of groundwater discharge and quantifying groundwtaer inflows into the stream, opening very promising perspectives for novel characterization of the groundwater/stream interfaces.