Structural hydrogeology of the Kénogami Uplands, Québec, Canada

Daphné Silva Pino, Thèse de Maîtrise.

Projet de Maïtrise en Sciences de la Terre sous la supervision du Pr. Alain Rouleau.

Description du projet

Characterizing the fracture network is a very significant component of investigations on fractured aquifers, as the secondary porosity controls the groundwater flow. It is also important to analyze the types of interactions between the fractures, e.g., the types of terminations and the dominancy of a certain fracture set, since such information helps to understand the tectonic events that were responsible for the generation of the fracture systems in the aquifer. Moreover, the current stress field is usually the most significant in controlling fracture aperture, which plays a major role in groundwater flow. 

The main objective of this research project is to characterize an aquifer in fractured crystalline rocks with a fairly homogeneous lithology, defining a hydrogeological model of the study area, through structural surveys at different scales and hydrogeologic data analyses. This study will be carried out in the Kénogami uplands, within the Saguenay graben, Quebec. This research shall help answering the following questions: 1) Is there a structured fracture system in the bedrock, that is, is it possible to identify preferential fracture orientations? 2) Can fracture systems be defined at different scales (e.g. regional and local ones)? If yes, are there any relationships between them? 3) Can any correlation between the fracture system(s) and the past and present stress fields be identified? 4) Is there a relationship between the hydrogeological properties obtained from boreholes and the fracture system(s)? 

There are three major steps in the present study. The first one consists of analyzing aerial photographs in order to identify lineaments and to select potential sites for fracture observation. The second phase includes field works, such as: general and detailed structural surveys on rock outcrops, which can be vertical walls or horizontal exposures; and geophysical logging, with particular interest in the acoustic televiewer. The third step combines the analysis of all data collected in the field, their comparison with the available hydraulic information from wells located in the crystalline rocks in the study area, and also the evaluation of differences and/or similarities among data from different scales. This shall finally allow characterizing the fractured aquifer and formulate a hydrogeological model for the study area. 

It is expected that this study will help to increase the comprehension about the fracture network where groundwater flows. More specifically, it shall provide a good characterization of the aquifer in fractured crystalline rocks in the Saguenay – Lac Saint-Jean region, allowing to describe how the fractures in bedrock affect the groundwater flow. Keywords: fractured aquifer, structural geology, hydrogeology

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