Characterisation of fracture network and groundwater preferential flow path in the Table Mountain Group (TMG) sandstones, South Africa

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.

Septic System Impacts on Source Water: Two Novel Field Tracer Experiments in Fractured Sedimentary Bedrock

“…Fluctuations in concentrations may therefore be attributed to the influence of the fracture network. The connectivity of fractures, which is influenced by fracture geometry controls the distribution and magnitude of hydraulic conductivity within the three-dimensional fracture network [85]. Solute concentration peaks occurred at different times, suggesting that preferential flow through multiple connected fractures with different attenuation along their pathways may be contributing solute from the septic bed to the CMT monitoring well.…”

Effects of land use change on streamflow and stream water quality of a coastal catchment

“…Farmers in the area made use of in-channel dams on the Duiwe River and tributaries on both the Touws and Duiwe Rivers. There is limited use of borehole water (DWAF, 2004) since the quartzitic sandstones of the TMG, such as in the Touws and upper Duiwe catchments, are highly fractured and faulted, limiting the storage of groundwater (Lin et l., 2014). The changing land use to pastures in the lower Duiwe catchment coupled with gentler slopes also decrease runoff (Singh et al, 2014).…”

Investigating Seawater Intrusion in Republic of South Africa’s Heuningnes, Cape Agulhas Using Hydrogeochemistry and Seawater Fraction Techniques

“…A multiparameter water quality probe was used to take EC readings in the field. The formula TDS (mg/L) = 0.65 × EC (µS/cm) was used to indirectly determine the total dissolved solids (TDS) values of groundwater from the EC values [24]. Using the classification of [25], TDS values were utilized to demonstrate the salinization level.…”