Preface
The study of fractured (hard rock) aquifers is increasingly pressing because they occupy vast areas of all continents, and the dependence on this type of aquifer for water supply is growing fast. In hard rocks, groundwater flows through void spaces that are present in fractures that form a connected network; its characterization requires knowledge of structural geology and rock mechanics. This book shows how these disciplines reveal the logical organization of a fracture network and helps to build more realistic conceptual models of groundwater systems.
The ability of hard rocks to supply water depends on the fracture connectivity and transmissivity, which are related to the size and orientation of fractures, as well as the width of the opening between fracture walls (i.e., aperture). These characteristics are constrained by the principles of structural geology and rock mechanics. This book provides insight regarding questions such as: How does the geometry of different fracture types influence fracture aperture and connectivity? How do tectonic regimes (compressive, extensional and strike slip) influence the general configuration of a fracture network? How does the brittle deformation history of a region affect the architecture and connectivity of the fracture system? How does the current in-situ stress field affect the aperture of fractures?
Different rock types such as sedimentary, volcanic, metamorphic and intrusive rocks have their own typical discontinuities and previously existing structures. These influence how the in-situ stresses contribute to developing their fracture network architectures. Conceptual models of fracture networks, their connectivity, and preferential groundwater flow pathways in different geological settings are presented and explained.
The heterogeneous distribution of fracture porosity in hard rock aquifers pose significant scientific and methodological challenges. One way of overcoming difficulties is to, when possible, conduct detailed fracture surveys on large rock exposures and apply the fundamental principles of structural geology and rock mechanics to develop a conceptual model of the fracture system. Such surveys provide an essential two- and three- dimensional complement to borehole data revealing the fracture-network geometry. As more surveys are conducted, knowledge on how fracture systems affect the groundwater flow and transport properties of rocks will gradually be expanded.