Imaging buried Quaternary valleys using the transient electromagnetic method

Jørgensen, Flemming; Sandersen, Peter B.E.; Auken, Esben

doi:10.1016/j.jappgeo.2003.08.016

Cited by 118 publications

(74 citation statements)

References 24 publications

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“…This is particularly true for data collected by airborne electromagnetic methods (AEM) because they can be collected quickly, densely, and at a relatively low cost for the very large spatial coverage (Steuer et al, 2008;Viezzoli et al, 2010b;Abraham et al, 2012;Faneca Sànchez et al, 2012;Refsgaard et al, 2014;Munday et al, 2015). Large-scale AEM (or ground-based EM) investigations have been used to delineate aquifers, aquitards, and buried valleys or other structures containing aquifers Jørgensen et al, 2003;Abraham et al, 2012;Oldenborger et al, 2013), to assess aquifer vulnerability Foged et al, 2014), to map saltwater intrusion (Fitterman and Deszcz-Pan, 1998;Viezzoli et al, 2010b;Lawrie et al, 2012;Herckenrath et al, 2013b), and to map freshwater resources (Steuer et al, 2008;Faneca Sànchez et al, 2012;Munday et al, 2015). The main drawbacks of electromagnetic (EM) data are (1) ambiguity in relating electrical properties to hydraulic properties, and (2) reduced lateral and vertical resolution with depth.…”

Section: Informing Hydrologic Models With Geophysicsmentioning

confidence: 99%

Testing alternative uses of electromagnetic data to reduce the prediction error of groundwater models

Christensen¹,

Christensen²,

Ferré³

2016

Hydrol. Earth Syst. Sci.

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Abstract. In spite of geophysics being used increasingly, it is often unclear how and when the integration of geophysical data and models can best improve the construction and predictive capability of groundwater models. This paper uses a newly developed HYdrogeophysical TEst-Bench (HYTEB) that is a collection of geological, groundwater and geophysical modeling and inversion software to demonstrate alternative uses of electromagnetic (EM) data for groundwater modeling in a hydrogeological environment consisting of various types of glacial deposits with typical hydraulic conductivities and electrical resistivities covering impermeable bedrock with low resistivity (clay). The synthetic 3-D reference system is designed so that there is a perfect relationship between hydraulic conductivity and electrical resistivity. For this system it is investigated to what extent groundwater model calibration and, often more importantly, model predictions can be improved by including in the calibration process electrical resistivity estimates obtained from TEM data. In all calibration cases, the hydraulic conductivity field is highly parameterized and the estimation is stabilized by (in most cases) geophysics-based regularization.For the studied system and inversion approaches it is found that resistivities estimated by sequential hydrogeophysical inversion (SHI) or joint hydrogeophysical inversion (JHI) should be used with caution as estimators of hydraulic conductivity or as regularization means for subsequent hydrological inversion. The limited groundwater model improvement obtained by using the geophysical data probably mainly arises from the way these data are used here: the alternative inversion approaches propagate geophysical estimation errors into the hydrologic model parameters. It was expected that JHI would compensate for this, but the hydrologic data were apparently insufficient to secure such compensation. With respect to reducing model prediction error, it depends on the type of prediction whether it has value to include geophysics in a joint or sequential hydrogeophysical model calibration. It is found that all calibrated models are good predictors of hydraulic head. When the stress situation is changed from that of the hydrologic calibration data, then all models make biased predictions of head change. All calibrated models turn out to be very poor predictors of the pumping well's recharge area and groundwater age. The reason for this is that distributed recharge is parameterized as depending on estimated hydraulic conductivity of the upper model layer, which tends to be underestimated. Another important insight from our analysis is thus that either recharge should be parameterized and estimated in a different way, or other types of data should be added to better constrain the recharge estimates.

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Section: Informing Hydrologic Models With Geophysicsmentioning

confidence: 99%

Testing alternative uses of electromagnetic data to reduce the prediction error of groundwater models

Christensen¹,

Christensen²,

Ferré³

2016

Hydrol. Earth Syst. Sci.

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“…Jorgensen et al (2003b) estimate resistivity thresholds to differentiate between sediments in buried valleys in Denmark. Accordingly, glacial sand has a resistivity greater than 60 m whereas clayey till sediments are placed between 25 and 50 m, and thus the exact cutoff value varies between study sites.…”

Section: Geophysical Datamentioning

confidence: 99%

“…Our study integrates high-resolution airborne geophysical data with borehole data to build a probabilistic classification of the subsurface at site. The geophysical data are collected by SkyTEM, an airborne transient electromagnetic method (TEM) that has been used extensively in Denmark for the purpose of groundwater mapping (Christiansen and Christensen, 2003;Jorgensen et al, 2003b;Sorensen and Auken, 2004;Auken et al, 2009). This study utilizes a method that translates SkyTEM observation data into facies probability, which enables associating the geophysical data with softness according to the level of uncertainty.…”

Section: Introductionmentioning

confidence: 99%

Challenges in conditioning a stochastic geological model of a heterogeneous glacial aquifer to a comprehensive soft data set

Koch

Jensen

et al. 2014

Hydrol. Earth Syst. Sci.

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Abstract. In traditional hydrogeological investigations, one geological model is often used based on subjective interpretations and sparse data availability. This deterministic approach usually does not account for any uncertainties. Stochastic simulation methods address this problem and can capture the geological structure uncertainty. In this study the geostatistical software TProGS is utilized to simulate an ensemble of realizations for a binary (sand/clay) hydrofacies model in the Norsminde catchment, Denmark. TProGS can incorporate soft data, which represent the associated level of uncertainty. High-density (20 m × 20 m × 2 m) airborne geophysical data (SkyTEM) and categorized borehole data are utilized to define the model of spatial variability in horizontal and vertical direction, respectively, and both are used for soft conditioning of the TProGS simulations. The category probabilities for the SkyTEM data set are derived from a histogram probability matching method, where resistivity is paired with the corresponding lithology from the categorized borehole data. This study integrates two distinct data sources into the stochastic modeling process that represent two extremes of the conditioning density spectrum: sparse borehole data and abundant SkyTEM data. In the latter the data have a strong spatial correlation caused by its high data density, which triggers the problem of overconditioning. This problem is addressed by a work-around utilizing a sampling/decimation of the data set, with the aim to reduce the spatial correlation of the conditioning data set. In the case of abundant conditioning data, it is shown that TProGS is capable of reproducing non-stationary trends. The stochastic realizations are validated by five performance criteria: (1) sand proportion, (2) mean length, (3) geobody connectivity, (4) facies probability distribution and (5) facies probability-resistivity bias.In conclusion, a stochastically generated set of realizations soft-conditioned to 200 m moving sampling of geophysical data performs most satisfactorily when balancing the five performance criteria. The ensemble can be used in subsequent hydrogeological flow modeling to address the predictive uncertainty originating from the geological structure uncertainty.

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“…Jørgensen et al [9] used the TEM method for 3D imaging of the cross-section of buried Quaternary valleys in Denmark. Their work studied several scenarios representing buried valleys for groundwater exploitation, and the 3D imaging was based also on constrained 1D…”

Section: Introductionmentioning

confidence: 99%

2D TEM Modeling for a Hydrogeological Study in the Paraná Sedimentary Basin, Brazil

Almeida¹,

Porsani²,

Santos³

et al. 2017

IJG

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This work uses 2D TEM (Transient Electromagnetic) modeling for a hydrogeological study in the Paraná sedimentary basin. The study area is located at the northern region of the state of São Paulo, Brazil, where groundwater is exploited from two aquifer systems: one sedimentary, shallow, and the other crystalline, deep. The interest in applying the TEM method in this area owes to the high exploitation rates of groundwater from the crystalline aquifer system for irrigation, which is triggering considerable seismic activity locally. This aquifer system is composed of fractured basalt within the Serra Geral Formation and is about 120 m deep. Eighty-six TEM soundings were acquired at this location, but in nine cases the data did not fit the modelled curve for 1D geoelectrical models due to the geological complexity of the area. This paper shows 2D geoelectrical modeling results based on the FDTD (Finite Differences in Time Domain) method to explain the lateral resistivity variation within the geological setting. A 2D model was generated for each sounding and compared with 1D inversion models as well as with direct information from wells. The results show some vertical variations of about 10 to 30 meters on the upper interface of the basalt layer from Serra Geral Formation. They are located at approximately 60 meters from the center of the soundings. The existence of these 2D structures in the subsurface can be related to the drainage system in the study area. The presence of these structures may indicate a connection between the shallow and deep aquifer systems, acting like a conduit that may contribute to the seismic activity reported.

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Imaging buried Quaternary valleys using the transient electromagnetic method

Cited by 118 publications

References 24 publications

Testing alternative uses of electromagnetic data to reduce the prediction error of groundwater models

Testing alternative uses of electromagnetic data to reduce the prediction error of groundwater models

Challenges in conditioning a stochastic geological model of a heterogeneous glacial aquifer to a comprehensive soft data set

2D TEM Modeling for a Hydrogeological Study in the Paraná Sedimentary Basin, Brazil

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Imaging buried Quaternary valleys using the transient electromagnetic method

Cited by 118 publications

References 24 publications

Testing alternative uses of electromagnetic data to reduce the prediction error of groundwater models

Testing alternative uses of electromagnetic data to reduce the prediction error of groundwater models

Challenges in conditioning a stochastic geological model of a heterogeneous glacial aquifer to a comprehensive soft data set

2D TEM Modeling for a Hydrogeological Study in the Paran&#225; Sedimentary Basin, Brazil

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Product

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2D TEM Modeling for a Hydrogeological Study in the Paraná Sedimentary Basin, Brazil