Analysis of the karst aquifer structure of the Lamalou area (He ´rault, France) with ground penetrating radar Walid Al-fares a,b , Michel Bakalowicz a , Roger Gue ´rin c, * , Michel Dukhan d a Universite ´ Montpellier II, CNRS Hydrosciences, c.c. MSE, 2 place Euge `ne Bataillon, 34095 Montpellier Cedex 5, France b AECS, B.O.Box 6091, Damascus, Syria c UMR 7619 Sisyphe, De ´partement de Ge ´ophysique Applique ´e, Universite ´ Pierre et Marie Curie (Paris 6), case 105, 4 place Jussieu, 75252 Paris Cedex 05, France d IRD, 911 avenue Agropolis, 34000 Montpellier, France Received 4 October 2001; accepted 23 August 2002 Abstract The study site at Lamalou karst spring (Hortus karst plateau) is situated 40 km north of Montpellier in France. It consists of a limestone plateau, drained by a karst conduit discharging as a spring. This conduit extends for a few dozen meters in fractured and karstified limestone rocks, 15 to 70 m below the surface. The conduit is accessible from the surface. The main goal of this study is to analyze the surface part of the karst and to highlight the karstic features and among them the conduit, and to test the performances of ground penetrating radar (GPR) in a karstic environment. This method thus appears particularly well adapted to the analysis of the near-surface ( < 30 m in depth) structure of a karst, especially when clayey coating or soil that absorbs and attenuates the radar is rare and discontinuous. A GPR pulseEKKO 100 (Sensors and Software) was used on the site with a 50- MHz antenna frequency. The results highlight structures characterizing the karstic environment: the epikarst, bedding planes, fractured and karstified zones, compact and massive rock and karrens, a typical karst landform. One of the sections revealed in detail the main conduit located at a depth of 20 m, and made it possible to determine its geometry. This site offers possibilities of validation of the GPR data by giving direct access to the karstic conduits and through two cored boreholes. These direct observations confirm the interpretation of all the GPR sections. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Ground penetrating radar (GPR); Karst; Cave; Epikarst; Karst plateau; South of France 1. Introduction In hydrogeology, ground penetrating radar (GPR) is applied to locate fractured or karstified zones, faults and cavities (Beres and Haeni, 1991; Holub and Dumi- trescu, 1994; Robert and de Bosset, 1994; McMechan et al., 1998; Beres et al., 2001), in aquifers (Sellmann et al., 1983; Arcone et al., 1998) as well in the study of the water contamination (Benson, 1995; Atekwana et al., 2000). Several studies also showed that this method of prospecting becomes, in certain cases, a more effective means in the study of karst than other geophysical methods like microgravity and electrical resistivity (Yelf and Creswell, 1988; Chamberlain et al., 2000). For a review of GPR investigations for karst, see also 0926-9851/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0926-9851(02)00215-X * Corresponding author. Tel.: +33-1-44-27-45-91; fax: +33-1- 44-27-45-88. E-mail address: [email protected] (R. Gue ´rin). www.elsevier.com/locate/jappgeo Journal of Applied Geophysics 51 (2002) 97 – 106
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Analysis of the Karst Aquifer Structure of the Lamalou Area
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Analysis of the karst aquifer structure of the Lamalou area
(Herault, France) with ground penetrating radar
Walid Al-faresa,b, Michel Bakalowicza, Roger Guerinc,*, Michel Dukhand
aUniversite Montpellier II, CNRS Hydrosciences, c.c. MSE, 2 place Eugene Bataillon, 34095 Montpellier Cedex 5, FrancebAECS, B.O.Box 6091, Damascus, Syria
cUMR 7619 Sisyphe, Departement de Geophysique Appliquee, Universite Pierre et Marie Curie (Paris 6),
case 105, 4 place Jussieu, 75252 Paris Cedex 05, Franced IRD, 911 avenue Agropolis, 34000 Montpellier, France
Received 4 October 2001; accepted 23 August 2002
Abstract
The study site at Lamalou karst spring (Hortus karst plateau) is situated 40 km north of Montpellier in France. It consists of a
limestone plateau, drained by a karst conduit discharging as a spring. This conduit extends for a few dozen meters in fractured
and karstified limestone rocks, 15 to 70 m below the surface. The conduit is accessible from the surface. The main goal of this
study is to analyze the surface part of the karst and to highlight the karstic features and among them the conduit, and to test the
performances of ground penetrating radar (GPR) in a karstic environment. This method thus appears particularly well adapted to
the analysis of the near-surface ( < 30 m in depth) structure of a karst, especially when clayey coating or soil that absorbs and
attenuates the radar is rare and discontinuous. A GPR pulseEKKO 100 (Sensors and Software) was used on the site with a 50-
MHz antenna frequency. The results highlight structures characterizing the karstic environment: the epikarst, bedding planes,
fractured and karstified zones, compact and massive rock and karrens, a typical karst landform. One of the sections revealed in
detail the main conduit located at a depth of 20 m, and made it possible to determine its geometry. This site offers possibilities of
validation of the GPR data by giving direct access to the karstic conduits and through two cored boreholes. These direct
observations confirm the interpretation of all the GPR sections.
D 2002 Elsevier Science B.V. All rights reserved.
Keywords: Ground penetrating radar (GPR); Karst; Cave; Epikarst; Karst plateau; South of France
1. Introduction
In hydrogeology, ground penetrating radar (GPR) is
applied to locate fractured or karstified zones, faults
and cavities (Beres and Haeni, 1991; Holub and Dumi-
trescu, 1994; Robert and de Bosset, 1994; McMechan
et al., 1998; Beres et al., 2001), in aquifers (Sellmann et
al., 1983; Arcone et al., 1998) as well in the study of the
water contamination (Benson, 1995; Atekwana et al.,
2000). Several studies also showed that this method of
prospecting becomes, in certain cases, a more effective
means in the study of karst than other geophysical
methods like microgravity and electrical resistivity
(Yelf and Creswell, 1988; Chamberlain et al., 2000).
For a review of GPR investigations for karst, see also
0926-9851/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved.