Surface water-groundwater interactions were studied in a coastal lagoon performing 180 seepage meter measurements and using heat as a tracer in 30 locations along a lagoon inlet. The direct seepage meter measurements were compared with the results from analytical solutions for the 1D heat transport equation in three different scenarios: (1) Homogeneous bulk thermal conductivity (Ke); (2) horizontal heterogeneity in Ke; and (3) horizontal and vertical heterogeneity in Ke.
The proportion of fresh groundwater and saline recirculated lagoon water collected from the seepage experiment was used to infer the location of the saline wedge and its effect on both the seepage meter results and the thermal regime in the lagoon bed, conditioning the use of the thermal methods.
The different scenarios provided the basis for a better understanding of the underlying processes in a coastal groundwater-discharging area, a key factor to apply the best-suited method to characterize such processes. The thermal methods were more reliable in areas with high fresh groundwater discharge than in areas with high recirculation of saline lagoon water.
The seepage meter experiments highlighted the importance of geochemical water sampling to estimate the origin of the exchanged water through the lagoon bed.
In heterogeneous aquifers, imaging preferential flow paths, and non-Gaussian effects is critical to reduce uncertainties in transport predictions. Common deterministic approaches relying on a single model for transport prediction show limitations in capturing these processes and tend to smooth parameter distributions. Monte-Carlo simulations give one possible way to explore the uncertainty range of parameter value distributions needed for realistic predictions. Joint heat and solute tracer tests provide an innovative option for transport characterization using complementary tracer behaviors. Heat tracing adds the effect of heat advection-conduction to solute advection-dispersion.
In this contribution, a joint interpretation of heat and solute tracer data sets is proposed for the alluvial aquifer of the Meuse River at the Hermalle-sous-Argenteau test site (Belgium). First, a density-viscosity dependent flow-transport model is developed and induce, due to the water viscosity changes, up to 25% change in simulated heat tracer peak times. Second, stochastic simulations with hydraulic conductivity (K) random fields are used for a global sensitivity analysis. The latter highlights the influence of spatial parameter uncertainty on the resulting breakthrough curves, stressing the need for a more realistic uncertainty quantification.
This global sensitivity analysis in conjunction with principal component analysis assists to investigate the link between the prior distribution of parameters and the complexity of the measured data set. It allows to detect approximations done by using classical inversion approaches and the need to consider realistic K-distributions.
Furthermore, heat tracer transport is shown as significantly less sensitive to porosity compared to solute transport. Most proposed models are, nevertheless, not able to simultaneously simulate the complementary heat-solute tracers.
Therefore, constraining the model using different observed tracer behaviors necessarily comes with the requirement to use more-advanced parameterization and more realistic spatial distribution of hydrogeological parameters. The added value of data from both tracer signals is highlighted, and their complementary behavior in conjunction with advanced model/prediction approaches shows a strong uncertainty reduction potential.
Event: EGU 2019 General Assembly, Vienna (Austria) Poster by Guilherme Nogueira, Christian Schmidt, Nico Trauth, Jan H. Fleckenstein
Stream-groundwater mixing zones are well known for their role in facilitating ecosystem metabolism which also results in enhanced water quality (e.g. by denitrification). However, due to their highly dynamic biogeophysical characteristics (i.e. temperature, flow directions, residence times), a simple and general quantification of the reactivity potential is not readily possible.
Here, we combined conservative and reactive tracer-tests with high frequency measurements of electrical conductivity (EC) and dissolved oxygen (DO) to enhance the understanding of the hydraulic variations on aquifer’s reactivity potential. We analysed the reactivity in terms of Damköhler numbers (DA) and assess its patterns over time and space, while comparing its dependency on short and long term temperature and river discharge fluctuations.
Event: EGU 2019 General Assembly, Vienna (Austria) Poster by Behzad Pouladi, Olivier Bour, Laurent Longuevergne, Jérôme de La Bernardie
Heat has been increasingly used as a tracer for characterization of the subsurface media both in fractured and porous aquifers. In fractured wellbore, understanding of the role of each fracture in total production of the fluid and the change of their contribution with change of the system conditions can help us increase our understanding about the system.
Considering the fact that when fluid being produced from an aquifer, the produced fluid experiences changing temperatures with depth while it travels up toward the surface and this change is related to the fluid velocity (flow rate), fluid properties as well as wellbore and formation properties. Using the Distributed Temperature Sensing (DTS) which in fact allows to measure the temperature both in time and space along the fiber optic, one can perform real time flow profiling and see the change of flow in each fracture with time.
In this work, a wellbore heat transfer model for a water production scenario, based on the wellbore heat transfer model presented by Hasan, Kabir  has been implemented in the MATLAB ® software. The model considers steady state heat transfer inside the wellbore and transient heat transfer from the wellbore to the formation. We use this analytical model to back calculate the flow rate in each section of the wellbores and thus flow contribution of each fracture using the temperature profile inside the wellbore.
The approach has been verified both numerically and experimentally. Distributed temperature data were recorded in different ambient and pumping flow rate in a fractured wellbore in Ploemeur site in Brittany, France. For cross validation, flow rates were also measured by Heat pulse flow meter.
The results show that model can predict real time contribution of each fracture to the total flow rate satisfactorily in different ambient and pumping rate. We also propose an automatic inflow zone (fracture/perforation location) detection which can help diagnosis of flowing zones (fracture locations). This model provides a basis for studying the transient behaviour and contribution of the fractures in different hydraulic conditions. For instance, the contribution of fractures in flow in different time of the years, studying the tidal effects on fracture flows, etc.