Abstract
Characterisation of fractured rocks and evaluation of fracture connectivity are essential for the study of subsurface flow and transport in fractured rock aquifers. In this study, we use a new method to present fracture networks and analyse the connectivity of the fractures, based on the technique of randomly-generated realisations. The application of the method aims to provide more detailed insights into the flow path and dynamics for sustainable utilisation of groundwater in the Table Mountain Group (TMG) aquifers, South Africa. Focusing on a representative wellfield in the TMG, the interpretation and integration of fracture data derived from field measurements, existing geological maps and remotely-sensed imagery, and observed responses of hydraulic tests, led to the development of a conceptual model for fracture network characterisation, which forms the basis of fracture connectivity analysis. The result shows that the a dominant number of the interconnected fractures are in the form of separated fracture clusters (networks) which is considered to be a common connectivity pattern in the TMG rocks and alike. The result also suggests that the connectivity pattern is collectively dependent on such factors as orientation, length, and density of fractures and implies that in a study domain only a small part of the fractures are responsible for flow circulation.
Highlights
Understanding, describing, and quantifying groundwater flow and chemical transport in fractured rocks require effective approaches to characterising fracture media
Based on the assumption that groundwater in the Table Mountain Group (TMG) sandstones is circulated through fracture networks, and in light of the field evidence, fractures were generated with the data derived from field measurements and remote sensing
This realisation is used to present, at a site scale, the geometric interconnection of fractures with length ranging from meters to tens of meters, and subsequently to yield a conceptual model that may be applied to the study of aquifer properties
Summary
Understanding, describing, and quantifying groundwater flow and chemical transport in fractured rocks require effective approaches to characterising fracture media. Fractures may act as conduits or barriers to groundwater flow, depending on their geometric and physical properties; of these, the connectivity of fractures is a critical factor controlling subsurface flow and transport (Margolin et al, 1998). Fracture connectivity is a measure of the interconnection of fractures and fracture networks. It controls the magnitude and distribution of hydraulic conductivity in the network and in the larger fractured aquifer system. 395), ‘ the term connectivity has no generally accepted definition, it is normally used to describe the subjective appearance of a fracture network. Chiles and De Marsily (1993) point out that fluid flow through fractures requires connectivity; ‘...if the fractures are not connected or form small clusters, no flow is possible, whereas if the fractures are highly connected, the system behaves like a continuous medium’ Connected networks are more permeable.’ Chiles and De Marsily (1993) point out that fluid flow through fractures requires connectivity; ‘...if the fractures are not connected or form small clusters, no flow is possible, whereas if the fractures are highly connected, the system behaves like a continuous medium’
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