References of "Kemna, A"
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See detailCalibration of seawater intrusion models: Inverse parameter estimation using surface electrical resistivity tomography and borehole data
Beaujean, Jean ULg; Nguyen, Frédéric ULg; Kemna, A. et al

in Water Resources Research (2014), 50(8), 6828-6849

Electrical resistivity tomography (ERT) can be used to constrain seawater intrusion models because of its high sensitivity to total dissolved solid contents (TDS) in groundwater and its relatively high ... [more ▼]

Electrical resistivity tomography (ERT) can be used to constrain seawater intrusion models because of its high sensitivity to total dissolved solid contents (TDS) in groundwater and its relatively high lateral coverage. However, the spatial variability of resolution in electrical imaging may prevent the correct recovery of the desired hydrochemical properties such as salt mass fraction. This paper presents a sequential approach to evaluate the feasibility of identifying hydraulic conductivity and dispersivity in density-dependent flow and transport models from surface ERT-derived mass fraction. In the course of this study, geophysical inversion was performed by using a smoothness constraint Tikhonov approach, whereas the hydrological inversion was performed using a gradient-based Levenberg-Marquardt algorithm. Two synthetic benchmarks were tested. They represent a pumping experiment in a homogeneous and heterogeneous coastal aquifer, respectively. These simulations demonstrated that only the lower salt mass fraction of the seawater-freshwater transition zone can be recovered for different times. This ability has here been quantified in terms of cumulative sensitivity and our study has further demonstrated that the mismatch between the targeted and the recovered salt mass fraction occurs from a certain threshold. We were additionally able to explore the capability of sensitivity-filtered ERT images using ground surface data only to recover (in both synthetic cases) the hydraulic conductivity while the dispersivity is more difficult to estimate. We attribute the latter mainly to the lack of ERT-derived data at depth (where resolution is poorer) as well as to the smoothing effect of the ERT inversion. [less ▲]

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See detailCharacterization of seawater intrusions using 2D electrical tomography
Nguyen, Frédéric ULg; Kemna, A.; Antonsson, A. et al

in Near Surface Geophysics (2009), 7

We have investigated the potential of 2D electrical imaging for the characterization of seawater intrusion using field data from a site in Almeria, SE Spain. Numerical simulations have been run for ... [more ▼]

We have investigated the potential of 2D electrical imaging for the characterization of seawater intrusion using field data from a site in Almeria, SE Spain. Numerical simulations have been run for several scenarios, with a hydrogeological model reflecting the local site conditions. The simulations showed that only the lower salt concentrations of the seawater-freshwater transition zone could be recovered, due to the loss of resolution with depth. We quantified this capability in terms of the cumulative sensitivity associated with the measurement setup and showed that the mismatch between the targeted and imaged parameter values occurs from a certain sensitivity threshold. Similarly, heterogeneity may only be determined accurately if located in an adequately sensitive area. At the field site, we identified seawater intrusion at the scale of a few kilometres down to a hundred metres. Borehole logs show a remarkable correlation with the image obtained from surface data but indicate that the electrically derived mass fraction of pure seawater could not be recovered due to the discrepancy between the in-situ and laboratory-derived petrophysical relationships. Surface-to-hole inversion results suggest that the laterally varying resolution pattern associated with such a setup dominates the image characteristics compared to the laterally more homogeneous resolution pattern of surface only inversion results and hence, surface-to-hole images are not easily interpretable in terms of larger-scale features. Our results indicate that electrical imaging can be used to constrain seawater intrusion models if image appraisal tools are appropriately used to quantify the spatial variation of sensitivity and resolution. The most crucial limitation is probably the apparent non-stationarity of the petrophysical relationship during the imaging process [less ▲]

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See detailFlow and Transport Monitoring in Soils and Aquifers using Electrical Resistivity Tomography
Vanderborght, J.; Kemna, A.; Köstel, J. et al

(2007)

Detailed reference viewed: 44 (3 ULg)
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See detailPotential of electrical imaging to constrain saltwater intrusion models: 2D numerical simulations
Kemna, A.; Nguyen, Frédéric ULg; Antonsson, A. et al

(2006)

Detailed reference viewed: 24 (7 ULg)