Event: AGU Fall Meeting 2019, San Francisco (USA)
Presentation by Joel Tirado-Conde, Majken Looms, Peter Engesgaard
Wetlands are extremely dynamical systems and their behavior depends on
the characteristics of the surroundings (topography, geology and
vegetation, among others) as well as on meteorological and hydrological
processes. Wetlands are wet partly because they receive groundwater (or
drain water) through diffuse upwelling and through springs. Studying
upwelling is of great importance to e.g. evaluate the overall ecology or
capacity to remove nitrate of the wetland system. One problem is that
diffuse upwelling is difficult locate and measure.
We analyze the temporal dynamics of a groundwater fed wetland in
central Jutland (Denmark) by the use of various thermal methods across a
lowland stream valley. A monitoring system consisting of Distributed
Temperature Sensing (DTS), wells with temperature depth profiles and
thermal infrared (TIR) imaging on a UAV, in conjunction with
hydrological and atmospheric data, provide a quasi 3D time-lapse
characterization of the thermal behavior of the system, both on the
ground and in the subsurface, over a period of around two years.
By analyzing the temporal evolution of the temperature in both the wetland surface and the groundwater, we can infer potential locations of groundwater upwelling to the land surface and subsequent overland flow. This is relevant as previous studies have shown that it is a generally overlooked flow component that may have a big impact relative to base flow. Moreover, it serves as a test for the feasibility of using heat as a tracer to study groundwater – surface water exchanges in wetlands.
More about ESR7 research project
More on Research Gate
in Geophysical Journal International Volume 220, Issue 2, February 2020, Pages 1187-1196
by Satoshi Izumoto, Johan Alexander Huisman, Yuxin Wu, Harry Vereecken
Induced calcite precipitation is used in geotechnics to modify the mechanical and hydrological properties of the underground. Laboratory experiments have shown that spectral induced polarization (SIP) measurements can detect calcite precipitation. However, the results of previous studies investigating the SIP response of calcite precipitation were not fully consistent.
This study aims to investigate how the SIP response of calcite depends on solute concentration to explain the differences in SIP response observed in previous studies. A four-phase experiment with SIP measurements on a column filled with sand was performed. In phase I, calcite precipitation was generated for a period of 12 d by co-injecting Na2CO3 and CaCl2 solutions through two different ports. This resulted in a well-defined calcite precipitation front, which was associated with an increase in the imaginary part of the conductivity (σ′′σ′′). In phase II, diluted solutions were injected into the column. This resulted in a clear decrease in σ′′σ′′. In phase III, the injection of the two solutions was stopped while calcite precipitation continued and solute concentrations in the mixing zone decreased. Again, this decreased σ′′σ′′. Finally, the injection rate of the Na2CO3 solution was reduced relative to that of the CaCl2 solution in phase IV. This resulted in a shift of the mixing zone away from the calcite precipitation front established in phase I and an associated decrease of σ′′σ′′.
These results imply that the SIP response of calcite is highly sensitive to the solute concentration near the precipitates, which may explain previously reported conflicting results.
Full article here
More on ESR12 research project
Event: Journées des Doctorants – Ecole Doctorale Géosciences, Ressources Naturelles et Environnement – Paris (France), 19/03/2019
Poster by Lara Blazevic, Ludovic Bodet, Laurent Longuevergne, Sylvain Pasquet, Damien Jougnot
More on ESR5 research project
Event: AGU Fall Meeting 2018, Washington DC (USA)
poster by Lara Blazevic, Ludovic Bodet, Damien Jougnot, Laurent Longuvergne
Seismic methods have been recently applied to the monitoring of spatial and temporal variations of near surface characteristics for hydrogeological purposes. The seismic signal is certainly related to mechanical properties that partly depend on porosity and saturation. The behavior of pressure (P) and shear (S) waves in the presence of water is partially decoupled, and the ratio of their propagation velocities VP/VS has been used to study water saturation changes.
However, the interpretation of the mechanical properties remains complex in unconsolidated near surface materials, limiting the quantitative description of linked hydrodynamic properties. In this study, we investigate the theories behind wave propagation velocities in poorly consolidated media and how they are affected by water content, focusing our discussion on the partially saturated response.
We present a field case where we used a Hertz-Mindlin based rock physics model to estimate water saturation from VP and VS from seismic data. The model is able to distinguish between dry and fully saturated areas at two distinct hydrological periods, but fails in identifying partially saturated areas in both cases. This work underlines the need for more elaborated models to infer hydrodynamic properties from seismic data.
More on AGU website
More on ESR5 research project
Event: EGU General Assembly, Vienna (Austria) 2019
Presentation by Anne-Karin Cooke, Cédric Champollion, Pierre Vermeulen, Nicolas Le Moigne and Sébastien Merlet
Ground-based gravity measurements can provide accurate constrains on the water storage dynamics of subsurface reservoirs. At the scale of the measurements time-lapse gravity experiments allow to monitor the water mass balance taking into account both the saturated and the unsaturated zone.
One major characteristic of the gravity measurement is the integration of all water masses across scales: gravity variations can be the effect of continentalscale soil humidity or aquifer (such as seen by GRACE measurements) and of local effects (such as the umbrellaeffect of a building or reservoir heterogeneities). The vertical gravity gradient is similar to gravity while showing a higher sensibility to local masses. The interest of the gradient for subsurface features such as caves is well known.
The objective of the presentation is the specific potential of gravity vertical gradient monitoring for water reservoir studies. The study is first based on existing measurements of gravity gradients time series (with a relative spring gravimeter): can significant hydro-logical signals be detected? Then based on numerical simulations, the potential of future ground-based for reservoir monitoring is investigated.
The capability of the gravity gradient method to detect heterogeneities (contrary to theclassical gravity) is evident: for example the classical Bouguer plate approximation often used to convert gravityinto equivalent water height (even in heterogeneous area such as karst) has no effect on the gravity gradient, hence new models need to be applied that combine gravity and gravity gradient measurements.
More about ESR8 Research Project