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3rd EEGS Meeting
- Conference date: 09 Aug 1997 - 11 Aug 1997
- Location: Aarhus, Denmark
- ISBN: 978-94-6282-128-6
- Published: 09 August 1997
41 - 60 of 124 results
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3-D FE-modeling of a mass movement on basis of geophysical investigations
Authors E. Castillo and F. KohlbeckA Iandslide has been modeled by three different models utilizing the FE-Program BMINES. The combination of several geophysical methods provided the information about the 3D-geometry of the slip and the range of some material properties. Seismic refraction surveys, geoelectrical soundings and electromagnetic measurements have been used for the characterization of the slip, location, depth, and physical properties of material.
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Electrostatic measurements in complex artificial (anthropogenic) grounds
Authors C. Panissod, A. Jolivet and A. TabbaghThe electrostatic method constitutes a generalization of the well known electrical method. As the electrostatic poles are located in the air, not far from the ground, the method can be used whatever the type of ground surface (tarmac, slabs, concrete,...).
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An evaluation of electromagnetic methods for waste site assessment
Authors L. Pellerin, D. L. Alumbaugh and M. Cathy PfeiferA baseline study in electromagnetic (EM) exploration of the shallow subsurface (< 10 m) was performed at the Idaho National Engineering Laboratory (INEL) Cold Test Pit (CTP) for the purpose of identifying and evaluating existing commercial and experimental instrumentation, integrating those technologies with multidimensional interpretational algorithms, and identifying gaps in shallow subsurface EM imaging technology.
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Predictive mapping of mechanical properties of alterites through continuous electrical resistivity measurements
Authors J. C. Gourry, R. Wyns and F. LebertBasement rocks constitute 25% of the surface geology of France. Throughout the geological record, and particularly during the Early Cretaceous and Paleogene, these rocks underwent significant weathering to form alterites more than 50 m thick in places. Later erosion incised vaileys in the alterites, which is why, in schistose areas, one may find aggregate quarries very close to day workings (for brick manufacture), the former being in the valley bottoms (minimum weathering) and the latter on the plateaus (maximum weathering). The aim of this research work is to assess the mechanical properties of these surface alterites in order to draw up maps for use in civil engineering sectors, such as excavation work for major communicatjon routes (roads, etc.) and laying underground pipes and cables (gas, electricity, telecommunication lines).
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A high density sampling survey of shallow karst features using EM and magnetic profiling techniques
Authors R. J. Sporry, A. Marquesda Costa, G. Desta, J. Roy and W. A. HugensDuring field experiments on high density sampling shallow EM (Geonics EM31) surveying near Moura, Portugal, it was found that a local shallow terrain depression showed enhanced rainwater infiltration and high apparent conductivity values (Sporry et. al. 1995). Other conductivity anomalies suggested a pattem correlating with the general geological strike direction (NW-SE).
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Flow training dikes for the Wouri estuary in Doula. DC prospection of sand in shallow sea water
Authors S. N‘Seke, B. Bagnérès, R. Lagabrielle and J. -L. MattiuzzoThe Port of Douala, which is located high up the Wouri River Estuary, is reached by means of a 50 km long access channel. The 25 km upper part of this channel currently requires intense and costly maintenance dredging. 20 years of dredging experience gained through three previous programs bas led the Cameroon National Ports Authonty (CNPA) to consider that an altemative solution with higher investment costs (flow training dikes) and reduced maintenance (by more than 60%) is the most appropriate in terms of present benefits.
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Outlook on geophysical evaluation of the ground conditions in the Kruja medieval castle, Albania
Authors A. Frasheri, L. Kapllani, F. Dhima and S. PeçiThe Castle of Kruja is the symbol of the culture and Albanian history. This castie is related with the most glorious epoch of the Albanian National Hero Skanderbeg.
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Relations between hydrogeologic and geoelectric parameters. A case study: The Setúbal peninsula, Portugal
Authors R. M. D. Gonçalves, A. R. Andrade Afonso and L. A. Mendes VictorThe Setubal Peninsula is located southern of Lisbon City, in the midst of Portugal (fig. 1). This belt (area) belongs to the Tejo and Sado river basins and it's located between them. It comprises the most important aquifer system of the country. Geohydrological data from the thousand water extraction wells, and more than one hundred Vertical Electric Sounding (VES) surveys exist from that region (fig. 2). Merging of these different data yields better knowledge about constitution and protection of the system.
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Logging techniques measuring parameters of water flow in wells - a critical review
More LessDuring the prospecting of a hydrogeological structure, a series of boreholes (wells) is usually drilled with the goal to get sufficient information on aquifers, their depth position, and their reservoir properties.
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Lowering of the ground water table - does it affect the fresh/salt water interface, and can we measure it?
Authors T. Vangkilde-Pedersen, H. Olsen and P. M. DuchThe Danish supply of potable water is mainly based on ground water. During construction work in areas with a shallow ground water table, temporary lowering of the water table is often necessary. In coastal regions, if the lowering of the water table is close to existing water abstraction sites, the ground water quality can be threatened by changes in the depth to the freshwater/saltwater interface. With an example from Vestamager near Copenhagen, Denmark a combination of geophysical methods for monitoring the freshwater/saltwater interface is demonstrated. The example ilustrates the advantages of combining geophysical well logging in observation wells with time domain electromagnetic (TDEM) soundings.
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The fresh and salt water distribution in the unconfined aquifer in northern Flanders
Authors W. De Breuck, E. Beeuwsaert and K. WalraevensThe interface between fresh and salt water in the unconfined aquifer of Zealand Flanders (The Netherlands) and the adjacent area in Belgium has been mapped by means of a resistivity survey controlled by many well observations, The interface corresponds with an interpreted formation resistivity equal to or less than 6 Ωm. The distribution pattern of fresh and salt water is tightly linked to the geological evolution of the area. Especially the latest phase of the Dunkirk transgression and the historical inundations have had a thorough influence.
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Seismic investigations of glacial structures in Northern Germany
Authors H. Wiederhold and G. CaspersShallow subsurface structures in Northem Germany and adjacent areas are characterized by glacial erosion and deposition. Thus, a system of up to 400 m deep channels mainly formed during the glaciation of the Elster period and filled with sediments afterwards is known and today of special interest for hydrological questions. Other glacial depressions, especially hollows with no outlet, are excellent sediment traps and afford optimum conditions for the study of stadial and interstadial deposits and thus, the reconstruction of climate and vegetation development during glacial epochs.
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Contribution from EM surveys to a regional groundwater resource quantification project in a hard rock area
Authors J. Roy, M. W. Lubczynski, R. J. Sporry and W. A. HugensThis note is dealing with two key concepts: the quantification of groundwater (GW) resources on one hand and the use of electromagnetic (EM) techniques on the other; these are the objects of this introduction.
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Detection of a volcanic aquifer by TDEM soundings
Authors G. Pagano, A. Menghini and S. FlorisThe purpose of this presentation is to show the great power of resolution of Time Domain Electromagnetics Methods in volcanics areas, in comparison with classic electric methods.
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Hydrogeophysical mapping with the transient electromagnetic sounding method
Authors L. H. Poulsen and N. B. ChristensenThe transient electromagnetic sounding method is an effective reconnaissance exploration tool for mapping good conductors like day and salt water. In the Bredebro area in Southem Jutland, Denrnark, the method has been used for mapping an aquifer situated in a Tertiary valley system eroded out in heavy day. The area was previously mapped with gravity measurements and this investigation indicated the presence of a Tertiary valley system. The transient electromagnetic investigation has confmed the location of the Tertiary valley found in the gravity investigation and added more information about the boundaries of the valley system.
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Hydrogeological investigations in the Bulawayo region, Matabeleland, Zimbabwe
Authors B. Lorentzen, Z. Dladla, P. Gwaze, T. Dahlin and N. B. ChristensenWithin the framework of hydrogeological studies for additional water supply for the city of Bulawayo, Zimbabwe, a cooperation between the University of Zimbabwe, Lund Technical University, Sweden, and the University of Aarhus, Denmark, with support from the Swedish International Development Agency has led to a geophysical survey of the large Kalahari and Karoo sedimentary basins in North Matebeleland, for the purpose of assessing water resources.
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1D joint inversion of radiomagnetotellluric (RMT) and transient-electromagnetic (TEM) data: an application for groundwater prospection in Grundfør, Denmark
Authors W. Schwinn and B. Tezkanin many parts of Europe the resources of ground water are short. A lot of these resources have a risk of contamination through agricultural activity, industry, waste deposits or salt water.
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Joint interpretation of radiomagnetotelluric and CVES measurements in the Grundfør area, Denmark
Authors M. K. Lauridsen and N. B. ChristensenThe radiomagnetotelluric (RMT) method has been used to collect data in the Grunfør area in Denmark to estimate the potential of the method under Danish conditions. The Grundfør area was chosen because it has been intensively mapped with several geophysical methods in connection with the Danish Environmental Research Programme. The results of previous measurements thus form a good basis for comparison.
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Three-dimensional geological model of the complex aquifers in an incised Quaternary valley in Jylland, Denmark
By P. GravesenDeep buried Quatemary valley systems incised into older pre-Quaternaiy deposits exist in many glaciated areas in northern Europe and North America and in the offshore areas of the North Sea basin and the Baltic Sea Basin. The valleys can reach several hundreds of meters below ground surface and they are fihled with diamictons and meltwater deposits. In Denmark the vaileys mainly occur in Jylland where i.e. Lykke-Andersen (1986) has investigated the structures and the formation of the vaileys.
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Statistical modelling of partial clay cover
By M. HansenOne of the major controlling factors for groundwater recharge in area of partial day cover is the distribution of the day bodies. In order to evaluate the distribution of a partial day cover in the Grundfør—Hinnerup area (Figure 1) and to quantify the probable distribution of the day cover a series of statistical simulations of the day distribution has been made.
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