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Pitfalls in the geological characterization of alluvial deposits; site investigation for reactive barrier installation at Aznalcollar, Spain

J. M. Salvany, J. Carrera, J. Bolzicco and C. Mediavilla
Pitfalls in the geological characterization of alluvial deposits; site investigation for reactive barrier installation at Aznalcollar, Spain
Quarterly Journal of Engineering Geology and Hydrogeology (May 2004) 37 (2): 141-154

Abstract

The alluvial deposits of the Agrio River in SW Spain have been studied using terrace mapping, boreholes, trenching and vertical electrical sounding to select an adequate place for a Permeable Reactive Barrier. Geological and hydrogeological data available prior to the barrier construction suggested a simple geological model based on three terraces, the most modern being deeper than the oldest. The barrier was accordingly trenched through the youngest terrace. However, excavation of the barrier and subsequent subsoil data demonstrated that the internal structure of the Agrio alluvial deposits does not follow such a simple model. A revised model, less favorable to the existing barrier design, revealed the oldest terrace to be deeper than the youngest, and to form a paleochannel oblique to the surface terraces and river trends. The study methods used are standard, but proved to have insufficient resolution to detect key features of the alluvial geology. It is concluded that such characterization methods, though widely used, are not appropriate where alluvial terraces may display complex internal structures not reflected in the modern surface geomorphology. In hindsight, the study area should have been larger, so as to encompass at least the width of the alluvial plain and to extend for a hundred meters or so up and downstream from the proposed barrier location. Lithological logs of the boreholes should have been carefully described from both cuttings and downhole geophysical logs, which would have allowed more accurate delineation of the stratigraphy of the alluvial deposit. Subsequent geophysical methods should have been calibrated to this stratigraphy to characterize the internal structure and basal contact of the alluvial deposit.


ISSN: 1470-9236
EISSN: 2041-4803
Coden: QJEGA7
Serial Title: Quarterly Journal of Engineering Geology and Hydrogeology
Serial Volume: 37
Serial Issue: 2
Title: Pitfalls in the geological characterization of alluvial deposits; site investigation for reactive barrier installation at Aznalcollar, Spain
Affiliation: Universitat Politecnica de Catalunya, Dep. Enginyeria del Terreny, Barcelona, Spain
Pages: 141-154
Published: 200405
Text Language: English
Publisher: Geological Society of London, London, United Kingdom
References: 36
Accession Number: 2005-040837
Categories: Engineering geologyEnvironmental geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., geol. sketch map
N37°15'00" - N37°15'00", W06°19'60" - W06°19'60"
Secondary Affiliation: Instituto Geologico y Minero de Espana, ESP, Spain
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from The Geological Society, London, London, United Kingdom
Update Code: 200525
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