- Title
- Groundwater exploration using borehole and geophysical techniques in the east of Raymond Mhlaba Local Municipality (formerly Nkonkobe Local Municipality) in the Eastern Cape Province, South Africa
- Creator
- Xanga, Sithule
- Subject
- Groundwater ecology
- Subject
- Geophysical instruments
- Subject
- Borehole gravimetry
- Date
- 2021-07
- Type
- Master's theses
- Type
- text
- Identifier
- http://hdl.handle.net/10353/22643
- Identifier
- vital:52616
- Description
- The study area lies in the eastern portion of Raymond Mhlaba Local Municipality (RMLM), formerly known as Nkonkobe Local Municipality within the Eastern Cape Province of South Africa in the southeastern portion of the main Karoo Basin. Its northen part is mountainous with high altitude of about 1500 m with dense vegetation, whereas the southern part attains low altitude of about 600 m with sparse vegetation. The entire study area is covered on the surface by the Beaufort Group sediments comprised of three geological formations namely Middleton Formation, Balfour Formation members (Oudeberg, Daggaboersnek, Baberskrans, Elandsberg, and Pilangkloof), and the Katberg Formation. Karoo igneous bodies (dolerite dykes and sills) intruded the sediments causing fracturing. The area receives mean annual precipitation of about 54 mm. It is semi-arid to dry with insufficient surface water resources and hence the need for this research to explore for potential groundwater. Many techniques were employed to reveal the surface and subsurface geology, including groundwater potential areas using climate data, vegetation cover, borehole data analysis, geological field mapping, rock samples collection for petrographic analysis, a density-porosity determination, magnetic data analysis, and electrical resistivity tomography. The study area was divided into seven sub-regions, SR1 to SR7. The climate data showed that the area experiences high monthly average temperatures of about 21.6 °C during the summer, and is a semi-arid to dry region. Vegetation cover is dense in the mountainous northern part of the study area. It receives comparatively high rainfall, experiences less evapotranspiration than the southern part the low altitude, receives less rainfall, and has relatively high temperatures and evapotranspiration. A total of 385 boreholes from the Department Water and Sanitation were analysed and these showed that sub-regions SR1 up to SR7 had average borehole depths ranging from 51.9 to 67.7 m, water strike depths from 13.8 to 21.7 m and yields from 0.8 to 1.9 L/s. Sub-regions SR2, SR4, SR5, while SR7 have an average yield ≥ 1.4 L/s up to 1.9 L/s and are classified in this study as having a good or high groundwater yield potential. Fifteen thin sections were studied indicating that the Beaufort Group has mudstone, shale and fine-grained sandstone. The latter was dominant in the studied thin sections with 70 – 80 % quartz, 15 – 20 % groundmass, 5 – 10 % of feldspars, 2 – 5 % biotite, and some had vein like cracks filled with clay cement. Laboratory studies show average dry densities for the formations vary from 2.44 to 2.65 g/cm3, and porosities range from 1.6 to 4.0 %. Magnetic grid data obtained from the Council for Geoscience (CGS) were reduced to the pole, first vertical derivative and analytic signal maps were generated to delineate magnetic sources in the sediments. The magnetic anomalies showed lineaments and ring-shaped patterns that were interpreted to be due to Karoo dykes and sills, respectively. Some of these intrusions are mapped on the geological map and quite a number are not mapped as they are under sediment cover. The intrusions are important in groundwater exploration as they would have caused fracturing of surrounding formations causing increased secondary porosity and permeability. Further, they are groundwater localisers. Electrical resistivity tomography (ERT) was carried out at 12 selected sites using the dipoledipole and Wenner-Schlumberger arrays, with a maximum cable length of 360 m was used with an approximate maximum depth of investigation of 70 m. Most of the sites’ inverted models show a low resistivity top layer of about 10 m thickness, which is inferred to be topsoil with moisture/water and or clayey content. A high resistivity second layer underneath the top layer, and is interpreted to be slightly weathered sandstone at its top grading into compact sandstones at the bottom of the investigation depth. Four site results show models with an intermediate layer between the top and bottom layers consisting of moderate resistivity values due to mudstones. Most of the models have vertical, narrow, low resistivity zones extending from the surface to the bottom layer, interpreted as fracturing. The top layer could be an unconfined aquifer during the wet months but is likely to dry up during the dry, hot months. The inferred fractures that extend deeper from the surface could be good groundwater targets to drill boreholes. Dolerite intrusions can act as natural groundwater barriers depending on their orientation hence such structures are the main targets when searching for groundwater. Vegetation cover observed on satellite images of remote sensing can be used along with other techniques to explore for groundwater. It is recommended that future ERT surveys should measure both electrical resistivity and induced polarization chargeability to discriminate between water and clay influence.
- Description
- Thesis (MSc) -- Faculty of Science and Agriculture, 2021
- Format
- computer
- Format
- online resource
- Format
- application/pdf
- Format
- 1 online resource (xvi, 182 pages)
- Format
- Publisher
- University of Fort Hare
- Publisher
- Faculty of Science and Agriculture
- Language
- English
- Rights
- rights holder
- Rights
- All Rights Reserved
- Rights
- Open Access
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Collections
UFH Department of Geology
| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | SOURCE1 | Xanga MSc Geology Dissertation.pdf | 14 MB | Adobe Acrobat PDF | View Details Download |