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Hydrogeological conceptual model of Sete Lagoas (MG) and associated implications of urban development in Karst region

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Author(s):
Paulo Henrique Ferreira Galvão
Total Authors: 1
Document type: Doctoral Thesis
Press: São Paulo.
Institution: Universidade de São Paulo (USP). Instituto de Geociências (IG/BT)
Defense date:
Examining board members:
Ricardo Hirata; Jose Luiz Albuquerque Filho; Augusto Sarreiro Auler; Didier Gastmans; Ivo Karmann
Advisor: Ricardo Hirata
Abstract

This research integrated geological, hydrogeological, geochemical, and stable isotope studies conducted in the municipality of Sete Lagoas (MG), Brazil, in order to understand the water circulation in a karst terrain and to propose alternatives for a better water use, aiming to avoid geotechnical problems. The area is constituted by Neoproterozoic limestones from the Sete Lagoas Formation, where karst conduits were developed, giving origin to the homonymous aquifer, which is covered by Cenozoic unconsolidated sediments and, occasionally, by Neoproterozoic metasedimentary rocks from the Serra de Santa Helena Formation. It was observed that in this aquifer the primary porosity is very low and the secondary porosity (micro -fractures) is also reduced, due to the filling by calcite. The great volume of groundwater migrates through the tertiary porosity characterized by two dominant solutionally enlarged bedding planes and, to a lesser extent, by sub-vertical enlarged fractures. The recharge, related to rainfall occurring from October to December, takes place through sinkholes, caves entrances, and where the limestones are under the Cenozoic sediments. A detailed study evaluating the scale effects also allowed the establishment of permeability distributions of the Sete Lagoas Aquifer. Other results obtained also established that the groundwater extractions are associated to karst geotechnical events located in the urbanized area of the municipality. The high groundwater extractions make the shallowest solutionally enlarged bedding plane, in some points, entirely in the unsaturated zone, causing geotechnical events. A geotechnical map identifies five levels of risk, based on the lithology and the groundwater level interaction. This type of mapping should guide the groundwater extractions and caring the urban land occupation in Sete Lagoas, preventing or delaying the occurrence of new subsidences or collapses. (AU)

FAPESP's process: 12/12846-9 - HYDROGEOLOGICAL CHARACTERIZATION AND AN IMPLEMENTATION OF A MANAGEMENT MODEL FOR UNDERGROUND WATER RESOURCES IN AQUIFERS KARST, SETE LAGOAS CITY (MG)
Grantee:Paulo Henrique Ferreira Galvão
Support type: Scholarships in Brazil - Doctorate