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Aquifer investigations in the Leon-Chinandega plains, Nicaragua, using electromagnetic and electrical methods

Corriols, Marvin LU ; Nielsen, Mette Ryom; Dahlin, Torleif LU and Christensen, Niels B. (2009) In Near Surface Geophysics 7(5-6). p.413-425
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... (More)
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. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Near Surface Geophysics
volume
7
issue
5-6
pages
413 - 425
publisher
EAGE
external identifiers
  • wos:000270895200011
  • scopus:77951064768
ISSN
1873-0604
language
English
LU publication?
yes
id
ed8cd3e9-9336-41a5-864b-7f16843d93c2 (old id 1505999)
date added to LUP
2009-11-23 16:30:32
date last changed
2017-08-20 03:44:58
@article{ed8cd3e9-9336-41a5-864b-7f16843d93c2,
  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.},
  author       = {Corriols, Marvin and Nielsen, Mette Ryom and Dahlin, Torleif and Christensen, Niels B.},
  issn         = {1873-0604},
  language     = {eng},
  number       = {5-6},
  pages        = {413--425},
  publisher    = {EAGE},
  series       = {Near Surface Geophysics},
  title        = {Aquifer investigations in the Leon-Chinandega plains, Nicaragua, using electromagnetic and electrical methods},
  volume       = {7},
  year         = {2009},
}