Application of time-domain electromagnetic method in mapping saltwater intrusion of a coastal alluvial aquifer, North Oman

El-Kaliouby, Hesham; Abdalla, Osman

doi:10.1016/j.jappgeo.2015.02.003

Cited by 35 publications

(14 citation statements)

References 9 publications

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“…Low resistivity values correlate with shallow depths of occurrence while elevated values congregate around the deeper parts of this layer. The elevated values ( 2 Ωm) for the saline layer is not an isolated case, as similar studies byNielsen et al (2006) andEl-Kaliouby and Abdalla (2015) have also modelled these values but at varying depths. Their assertion of seawater being the main determinant of such resistivity is a view shared widely by these studies.…”

supporting

confidence: 66%

“…These are typical of the method and were among issues encountered by Verave (2018) from which the current study advances with the application of Time Domain or Transient ElectroMagnetic resistivity method (TDEM or TEM). TEM is a relatively new method but fast becoming popular (El-Kaliouby & Abdalla, 2015;Shaaban et al, 2016;Ezersky & Frumkim, 2017;Leite et al, 2018) not only because of its ability to overcome issues faced by the DC method but primary because of sampling accuracy and its high spatial density.…”

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confidence: 99%

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Mapping Saltwater Intrusion using Transient ElectroMagnetic Data in Maopa, Central Province, Papua New Guinea

Verave¹

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<p>Saltwater intrusion studies in coastal Papua New Guinea (PNG) are a rarity despite recognized vulnerabilities to salination of coastal groundwater resources. For many seaside communities such as Maopa the threat of salination is exacerbated by high extraction rates by a growing population and the likelihood of the effects of climate change. Saltwater intrusion can be addressed using various methods, including direct water sampling from wells and electrical resistivity measurements. This study advances knowledge of a previous assessment of saltwater intrusion and groundwater in this region that used DC Schlumberger resistivity soundings, through an extensive and cost-effective Transient ElectroMagnetic (TEM) survey. The study aims to map the lateral and vertical extent of salination and the characterization of groundwater in the landward direction over seven lines of TEM soundings along Keakalo Bay. The TEM method proved successful in identifying four main geoelectric layers. The top layer has a highly variable resistivity (range of 5 to 355 Ωm) inferred as the vadose zone. Beneath this layer is a layer of intermediate resistivity (100 Ωm > p ≥ 20 Ωm) characterizing a perched freshwater aquifer with a thickness range of 3.2 to 15 m. An intermediate layer of low resistivity (20 Ωm > p ≥ 3 Ωm) was detected at the boundary separating the freshwater aquifer from the inferred saltwater intrusion. This layer is typically thicker than the freshwater aquifer and is referred to as the mixing zone. The deepest layer constituting the salination zone has a very low resistivity (3 Ωm > p ≥ 0.4 Ωm), occurring at depths of up to 42 m. The depth to the salination zone varied from deep in the middle of the survey area to shallow in the fringes of the survey. This pattern is reflective of surface seawater infiltration marked by mangrove forest in the interior and subsurface infiltration from the coast. Similar depth trends but at shallower depths were also observed for the mixing zone, and the freshwater region. In some cases the mixing area overwhelms the freshwater regions. Layering confirmed groundwater resource and salination patterns as those of basic models reflective of small island hydrology, except that salination and the freshwater boundary were less distinctive due to the relatively high thickness of the dispersion zone. The use of different sounding parameters in line 7 provided useful information about the nature of the deep basement unit and thickness of the overlying unconsolidated quaternary sediment.</p>

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confidence: 66%

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confidence: 99%

Mapping Saltwater Intrusion using Transient ElectroMagnetic Data in Maopa, Central Province, Papua New Guinea

Verave¹

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“…In addition, head fluctuations detected at a well in the mixing zone between fresh and salt water can be much higher than those taking place in the actual aquifer (Shalev et al, 2009). Direct salinity measurements can be complemented by geophysical campaigns (e.g., Beaujean et al, 2014;El-Kaliouby & Abdalla, 2015;Kourgialas et al, 2016;Pidlisecky et al, 2015). Salinity data associated with an Integrated Depth Sampling approach represent an integral value along a borehole screen and may not be suitable to fully constrain a SWI model.…”

Section: Challenges Of Parameter Estimation In Density-dependent Flowmentioning

confidence: 99%

Data Assimilation in Density‐Dependent Subsurface Flows via Localized Iterative Ensemble Kalman Filter

Xia

Tong

et al. 2018

Water Resources Research

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Parameter estimation in variable‐density groundwater flow systems is confronted with challenges of strong nonlinearity and heavy computational burden. Relying on a variant of the Henry problem, we evaluate the performance of a domain localization scheme of the iterative ensemble Kalman filter in the framework of data assimilation settings for variable‐density groundwater flows in a seawater intrusion scenario. The performance of the approach is compared against (a) the corresponding domain localization scheme of the ensemble Kalman filter in its standard formulation as well as (b) a covariance localization scheme of the latter. The equivalent freshwater head, hf, and salinity, Sa, are set as the target state variables. The randomly heterogeneous field of equivalent freshwater hydraulic conductivity, Kf, is considered as the system parameter field. Density‐independent and density‐driven flow settings are considered to evaluate the assimilation results using various methods and data. When only hf data are assimilated, all tested approaches perform generally well and a localization scheme embedded in the iterative ensemble Kalman filter appears to consistently outperform the domain localized version of the standard ensemble Kalman filter (EnKF) in a density‐driven scenario; Dirichlet boundary conditions tend to show a more pronounced negative effect on estimating Kf for density‐independent than for density‐dependent flow conditions; hf data are more informative in a density‐dependent than in a density‐independent setting. The sole use of Sa information does not yield satisfactory updates of hf for the covariance localization scheme of the standard EnKF, while the sole use of hf does. The domain localization scheme leads to difficulties in the attainment of global filter convergence when only Sa data are used. A covariance localization scheme associated with a standard EnKF can significantly alleviate this issue.

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“…In the geophysical exploration area, the electromagnetic method instrument has an important role [1][2][3][4]. The method is used in coal mine, metallic minerals, and geological mapping, etc.…”

Section: Introductionmentioning

confidence: 99%

Input Power Factor Control of Matrix Converter Based Transmitter for Transient Electromagnetic Sounding

Li¹

2018

Preprint

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Three-phase to single-phase matrix converter (TSMC) is used as the transmitter for transient electromagnetic method (TEM) instrument, instead of an AC-DC converter and an H-bridge inverter.The transmitter produces excitation current for primary field. The output current has a waveform with a bipolar square of half duty cycle, which is required by TEM. The space vector PWM based on input currents is discussed in detail. The control method of input power factor is proposed for TSMC. The simulation model of TSMC is established and the simulations of different conditions are completed.The simulation results show the controllability of the input power factor is illustrated.

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Application of time-domain electromagnetic method in mapping saltwater intrusion of a coastal alluvial aquifer, North Oman

Cited by 35 publications

References 9 publications

Mapping Saltwater Intrusion using Transient ElectroMagnetic Data in Maopa, Central Province, Papua New Guinea

Mapping Saltwater Intrusion using Transient ElectroMagnetic Data in Maopa, Central Province, Papua New Guinea

Data Assimilation in Density‐Dependent Subsurface Flows via Localized Iterative Ensemble Kalman Filter

Input Power Factor Control of Matrix Converter Based Transmitter for Transient Electromagnetic Sounding

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