HR: 11:35h
AN: H42B-06 INVITED     [Abstracts]
TI: Large-scale hydrogeophysical characterization for sustainable groundwater development in a semi-arid terrain in NE Brazil using a combined TEM-AMT approach
AU: * Fontes, S L
EM: sergio@on.br
AF: Observatório Nacional, Gal José Cristino 77, Rio de Janeiro, RJ 20921 400, Brazil
AU: Meju, M A
EM: m.meju@lancaster.ac.uk
AF: Lancaster University, Lancaster LA1 4YW, Lancaster, LA1 4YW, United Kingdom
AU: La Terra, E F
EM: laterra@on.br
AF: Observatório Nacional, Gal José Cristino 77, Rio de Janeiro, RJ 20921 400, Brazil
AU: Nascimento, F
EM: flavia_nas@yahoo.com.br
AF: Observatório Nacional, Gal José Cristino 77, Rio de Janeiro, RJ 20921 400, Brazil
AB: Accurate identification of groundwater sources in granular deposits and crystalline basement and preventative mapping of their recharge zones to aid sustainable development are major issues in semi-arid terrains. We propose that combined TEM-AMT surveying has the potential to contribute towards finding solutions to both problems and demonstrate this using a major case study in semiarid northeast Brazil. Combined TEM-AMT and TEM-CSAMT surveys were carried out along several profiles (totaling around 220 line km) at the southeastern margin of Parnaiba basin in NE Brazil to determine structural controls on groundwater distribution, pin-point zones for drilling and delineate potential recharge zones. The profiles transect sedimentary and bordering Precambrian crystalline terrains and in particular, cut across linear basin-border grabeform structures suggested by previous aeromagnetic surveys. Localised studies in wholly crystalline terrains were also conducted near several small communities. The AMT-CSAMT data were corrected for static shift using collocated TEM soundings. Two-dimensional regularized inversion of AMT-CSAMT data was carried out for all profiles. For the basin-margin studies, the contact between the sedimentary and crystalline basement rocks was well imaged on all profiles and graben-like structures mapped near the basin borders on some of the transects are suggested for deep drilling for groundwater. 2D inversion results from TEM-CSAMT measurements on 6 profiles were able to map important fault structures cutting across the basin which appear to connect sedimentary aquifers with fracture-zone basement aquifers in the area and are interpreted as important recharge zones. This finding is supported by evidence from very productive wells located along these fault structures. We suggest that the combined TEM- AMT approach is the way forward for such semi-arid environments.
DE: 1835 Hydrogeophysics
DE: 1859 Rocks: physical properties
DE: 1895 Instruments and techniques: monitoring
SC: Hydrology [H]
MN: 2007 Joint Assembly