>Magister Scientiae - MSc / Crystalline basement aquifers are an important source of water supply in sub-Saharan Africa for various purposes. These aquifers are characterized by fractured rock networks which form pathways for groundwater recharge, flow, and discharge in subterranean groundwater areas. The fractured rock networks in these areas form fractured rock aquifers which in some cases are protected or reserved. In South Africa, various aquifers with these characteristics have been declared as subterranean groundwater control areas. The physical characteristics of these hydrogeological settings remains crucial in sustaining ecosystems and supporting socio-economic practices such as irrigation, among others. However, the role of fracture connectivity in crystalline basement aquifers remains poorly understood despite the well-established knowledge about the hydrogeological characteristics of such areas. / 2022

Stockholm archipelago is a combination of coastal and young glaciated conditions on hard rock geology with almost no primary porosity and very limited secondary porosity. Therefore the aquifer is both of limited capacity and exposed to salinity problem. In this context importance of fractures and soil cover is magnified. Lineaments are representatives of fractures in remote sensing. Fracture mapping in study area proves close correspondence between orientation of fractures and nearly located lineaments. Especially in this type of terrain, lineaments normally occur together with many other interesting hydrogeological features such as topographic attributes, soil, and vegetation; however, still each of these factors has its own effect on the groundwater situation. Through employment of geostatistical analysis and a modified variant of the RV (Risk Variable) method, called the PV (Probability Value) method, different attributes are rated by importance. The results show, soil cover is the most influencing factor then rock type and distance from lineaments; other factors are classified after them. It is discovered that the center of lineaments may not be the most suitable site to extract water because of being clogged by fills. This is particularly the case for shear fractures in which clay can be internally formed due to friction. Based on the statistical results a model is made in GIS environment in order to create hydrogeological maps. Such maps, after validation, can be used for any other area with similar properties even with missing or very limited data from boreholes. These maps definitively are only probability maps projecting areas with higher and lower prospect of aquifer potential and cannot guarantee high capacity in every borehole drilled in designated areas due to high heterogeneity of fractured rock system. Analysis of chemical data from wells proves a correlation between fracture orientations and topography with salinization and groundwater flow. Groundwater flow in the surroundings seems to be essential for feeding the aquifer as most of the wells with increased salt content have also low capacities.