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Hydrogeology of basement aquifers in the Limpopo Province
Expanded Title:Almost the whole continent of Africa is underlain by crystalline Basement rocks, albeit in places under a thick cover of more recent material. Consequently, crystalline Basement rocks form the largest of the four major aquifer domains or “hydrogeological provinces” found in sub-Saharan Africa, covering about 40% of the region’s 23.6 million square kilometres. Crystalline Basement aquifers differ in important ways from other aquifer types, and demand specific knowledge and techniques if groundwater is to be extracted and managed efficiently. The study covered two distinct geological and morpho-structural domains within the Limpopo Province, the Limpopo Plateau in the west and the Letaba Lowveld in the east, together covering about 23 500 km2. The basement rocks of the Limpopo Province are structurally complex, shaped by multiple tectono-metamorphic events spanning at least 600 million years. The borehole dataset compiled for the study consisted of over 8 000 boreholes contained in the Groundwater Resources Information Project (GRIP) Limpopo database of the South African Department of Water Affairs. Approximately 3 000 of these boreholes have been hydraulically tested and the lithology has been recorded for 1 200. The basement lithologies of the study area are characterised by a generally thin regolith overlying a primarily structurally controlled fractured aquifer. Compared to the Letaba Lowveld, the Limpopo Plateau is generally characterized by deeper boreholes due to deeper water strikes, water levels, weathering and fracturing depths. Geology has a clear influence, with boreholes exploiting intergranular aquifers composed of highly permeable material showing generally higher yields. Other identified favourable groundwater targets are the metamorphic aureoles of younger granite intrusions and complexes. Despite the local importance of the regolith as a recharge and storage mechanism for the underlying fractured bedrock, no correlation between borehole yields and depth of weathering was found. A differentiated pattern of lineament, shear zone and dyke orientations in the different domains let to a more complex conceptual model of groundwater occurrence and borehole productivity. This conceptual model is inconsistent with the predicted regime based on regional stress field data and suggests that local variations have a strong influence on groundwater occurrence.
Date Published:01/03/2011
Document Type:Research Report
Document Keywords:Hydrology, Ground Water
Document Format:Report
Document File Type:pdf
Research Report Type:Standard
WRC Report No:1693/1/10
ISBN No:978-1-4312-0082-5
Authors:Witthüser KT; Holland M; Rossouw TG; Rambau E; Bumby AJ; Petzer KJ; Dennis I; Beekman H; van Rooy JL; Dippenaar MA; de Wet LM
Project Leader:Witthüser KT
Project No:K5/1693
Document Size:60 984 KB
Attachments:Executive Summary 1693.pdf
Table of contents 1693.pdf
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