| 1. |
- Corriols, Marvin, et al.
(author)
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Geophysical characterization of the Leon-Chinandega aquifer, Nicaragua
- 2008
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In: Hydrogeology Journal. - : Springer Science and Business Media LLC. - 1431-2174 .- 1435-0157. ; 16:2, s. 349-362
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Journal article (peer-reviewed)abstract
- Electrical geophysical surveys in the mode of vertical electrical soundings (VES) and continuous vertical electrical soundings (CVES) were conducted in the Leon-Chinandega plains, northwestern Nicaragua, in order to obtain detailed information about the geometry of the different hydrogeological layers in the aquifer and depth to the basement. A total of 51 VES were carried out within the plains. The results show a complex structure towards the north east of the area, and the southwestern part of the plains presents a smoother stratification. The geoelectrical measurements and borehole information indicate that the basement topography is characterized by hills and deep valleys with highly variable basement depths. Fifty CVES where done in a smaller area in the center of the plain. The resistivity data yielded considerable information revealing the existence of two main geo-electrical units. The combined interpretation of geological and geophysical data shows an environment typical of sedimentary volcanic coastal plains. The information collected during this investigation provides valuable data for estimating the fresh-water resources of the Leon-Chinandega aquifer system and for development of a groundwater management plan.
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| 2. |
- Mendoza, Jose Alfredo, et al.
(author)
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Aquifer interactions with a polluted mountain river of Nicaragua
- 2008
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In: Hydrological Processes. - : Wiley. - 1099-1085 .- 0885-6087. ; 22:13, s. 2264-2273
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Journal article (peer-reviewed)abstract
- The interactions between a stream and nearby shallow aquifers were investigated in a mountain basin being polluted by mercury released during mining in central Nicaragua. Hourly data series of water levels and temperatures were analysed using cross-correlation. Resistivity imaging was used to map the subsurface and to complement the hydrological data interpretation. The results show the complex hydrogeological conditions that characterize the region, with weathering and fractured rock as main contributors to groundwater transport. The resistivity images suggest the presence of two vertical dykes perpendicular to the stream, and zones rich in clay. The data series indicate a rapid response from the aquifers to recharge events, followed by immediate discharge on a yearly basis. Furthermore, alternating periods of stream infiltration and aquifer discharge were identified. This work demonstrates that surface water pollution is a threat to groundwater quality in the area.
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| 3. |
- Corriols, Marvin, et al.
(author)
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Aquifer investigations in the Leon-Chinandega plains, Nicaragua, using electromagnetic and electrical methods
- 2009
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In: Near Surface Geophysics. - 1873-0604. ; 7:5-6, s. 413-425
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Journal article (peer-reviewed)abstract
- The Leon-Chinandega plains are located in the north-western part of Nicaragua and represent the most important groundwater reservoir of the country. The aquifer is comprised of three hydrogeological units. The top unit is an unconfined alluvial and below a more consolidated volcanic aquifer is found. These aquifers rest on an ignimbrite unit that acts as the basement of the aquifer. The plains are mainly used for agricultural purposes and most of the irrigation comes from upper aquifer wells (not deeper than 70 m) allocated within the shallow unconfined aquifer. Transient electromagnetic soundings (TEM) and continuous vertical electrical soundings (CVES) were carried out in order to obtain information regarding the geology of the study area. Two TEM profiles extending from the Pacific coast towards the volcanic chain were carried out with an approximate separation between soundings of 250 metres. A grid of TEM soundings was also performed in an area located between the towns of Posoltega and Quezalguaque. CVES were carried out in different areas of the plains in order to obtain detailed information on the geology and distribution of the shallow aquifer. This information was later correlated with information available from wells in the area. One of the objectives of this investigation was to test and evaluate the applicability of the TEMfast48 equipment in the study area. In the plains area the TEM method shows very good results where a general geophysical model of mostly a three-layered earth can be obtained. In the coastal areas the models are more irregular and complex. The results from the CVES generally agree with the TEM models but present more details, especially in areas of complex geology. The penetration depth for the TEM soundings reached almost 100 m at most, depending on the depth to a low resistivity layer. In some areas the depth to the basement was estimated with long-layout CVES. In general, it was possible to obtain consistent geoelectrical models of the area and the methods complement each other well. The geoelectrical models are an excellent addition to other investigation methods as they provide an overview of the aquifer system and can serve as a basis for refining the conceptual and numerical models of the aquifer system. This information is expected to become very valuable for the exploration, management and protection of the groundwater resources in the Leon-Chinandega plains to ensure sustainability of the resource.
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| 4. |
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| 5. |
- Parrales, Rainer, et al.
(author)
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Site investigation with combined methods in a faulted area in Managua, Nicaragua - a pre-study
- 2003
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In: Procs. 9th Meeting Environmental and Engineering Geophysics, Prague, Czech Republic, 31 August-4 September 2003.
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Conference paper (peer-reviewed)abstract
- Geophysical methods are increasingly being applied to geotechnical investigations, as they can identify material properties and material boundaries, as well as variations in space and time of relatively large volumes of soil. Another advantage is that many of these methods are non-intrusive. The combination of several methods and the verification of their results by sampling and correlating with geotechnical methods are advisable in order to improve the reliability of geophysical investigations. In this case we used the following geophysical methods; combined resistivity and time domain induced polarisation (IP) two-dimensional imaging (CVES), seismic refraction plus multi-channel analysis of surface waves (MASW). The geophysical results are compared to a geologically documented trench, which had been dug 5m south of the geophysical line with a N65°W orientation. The trench intercepted an active fault zone. The geological study determined that the intercepted fault zone corresponds to the Escuela Fault System, one of a many of the complex faulting system within the so-called Managua Graben.
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| 6. |
- Dahlin, Torleif, et al.
(author)
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Multiple-gradient array measurements for multichannel 2D resistivity imaging
- 2006
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In: Near Surface Geophysics. - 1873-0604. ; 4:2, s. 113-123
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Journal article (peer-reviewed)abstract
- Two-dimensional resistivity imaging using multiple gradient, Wenner and dipole-dipole electrode arrays was carried out at two field sites in Sweden and one in Nicaragua, with the objective of confirming the practical applicability of results obtained with numerical modelling. The results support earlier numerical modelling studies that concluded that the gradient array, using multiple current electrode combinations, has resolution as good as or better than the commonly used Wenner array. The array behaved well in terms of sensitivity to noise at the test sites, and the results obtained generally agree with dipole-dipole array results, although the latter at two of the sites gave resistivities that differed significantly from the other arrays in the deeper parts of the inverted models. A formula proposed for pseudosection plotting works well for data quality assessment, where it can be an advantage to make separate plots for each m-factor (the distance between the midpoints of the current and potential electrode pairs) or for each a-spacing. The gradient array is well suited for multichannel data acquisition, and can significantly increase the speed of data acquisition in the field and at the same time give higher data density, but it is also an attractive option for single-channel data acquisition. The Wenner array, on the other hand, is not suitable for measuring in more than one channel. Compared to the dipole-dipole array, it offers lower sensitivity to noise which may be a major advantage in real data acquisition, and the remote electrode needed for the pole-dipole array is avoided, which is often a significant advantage for field logistics.
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