Estimating variations in groundwater fluxes and direction using a combined Active-DTS - FVPDM (tracer experiment): experimental validation and modelling

The coupling of Active-DTS and FVPDM methods in a Lower Cretaceous chalk aquifer showed complementary results alowing to characterize the groundwater flux variations. While the Active-DTS method is using a heated fiber optic (FO) cable placed in the gravel pack outside the borehole, the FVPDM method is making measurements inside the borehole. The Active-DTS method gives a distributed information of the groundwater flux at points in depth while the FVPDM method is integrating the measurement of the GW flow rate crossing the screen. This experiment shows the high potential of the Active-DTS method to estimate the groundwater flow rate along the depth of a borehole if we could controle the position of the FO cable. Further modelling results show that using multiple FO cables not only allows reducing the uncertainty of the groundwater flux estimation but also the estimation of the groundwater flow direction.