- Title
- A hydrogeological investigation of Grahamstown, assessing both the dynamics and quality of the local groundwater system
- Creator
- Smetherham, Kyle Norman
- ThesisAdvisor
- Hughes, Denis
- ThesisAdvisor
- Tanner, Jane
- Subject
- Hydrogeology -- South Africa -- Makhanda
- Subject
- Water quality -- South Africa -- Makhanda
- Subject
- Groundwater -- Quality -- South Africa -- Makhanda
- Date
- 2019
- Type
- text
- Type
- Thesis
- Type
- Masters
- Type
- MSc
- Identifier
- http://hdl.handle.net/10962/94444
- Identifier
- vital:31045
- Description
- In many parts of South Africa, complete allocation of surface water reservoirs together with current drought conditions has led to serious water shortages and subsequent awareness regarding the importance to save water. Grahamstown is no different, with water problems relating to low supply and high demand being compounded by insufficient treatment capacity and aging infrastructure. Groundwater is an alternative water resource that could potentially act as a supplementary and/or emergency supply to the town, reducing the reliability on surface reservoirs. Groundwater however, is a hidden resource and requires an understanding of various aquifer properties and continuous monitoring and modelling so not to permanently disrupt the natural system but rather achieve sustainable management. Grahamstown is situated towards the northern extent of the Cape Fold Belt (CFB) system, within a synclinal fold structure. The local geology forms two local aquifer systems beneath Grahamstown that directly influence both the dynamics and quality of the groundwater. These underground reservoirs are the Witpoort and Dwyka aquifers and can be described as a semi-confined, fractured, quartzitic sandstone aquifer and an unconfined, fractured, tillite aquifer, respectively. Separating these aquifer systems is a shale aquitard, although due to the fractured nature of the rocks in the region there is most likely some groundwater interaction between them. Evaluation of geological formations together with the monitoring of 31 local boreholes presented a valuable conceptualisation of the local system and allowed for the application of methods to estimate recharge. Recharge estimation is one of the most crucial factors when managing aquifer systems as it can be used to determine what proportion of rainfall contributes to the subsurface reservoir and therefore, the sustainable amount that can be extracted. Various methods have been developed to estimate recharge, however due to the uncertainty surrounding groundwater systems, especially fractured aquifers, it was important to apply multiple methods to validate results. The water-table fluctuation (WTF) and cumulative rainfall departure (CRD) are two methods that were used in the present study to determine recharge. These methods rely on water-table changes in boreholes and specifically how they respond to rainfall events. Along with the WTF and CRD methods, a modelling approach was also used to estimate recharge which focused on the dynamics of a natural groundwater outlet, termed the Fairview Spring. This natural spring system is located just outside the main town of Grahamstown, within the Witpoort aquifer system, and is an important water resource to many residents due to poor supply and quality of municipal water. Monitoring the discharge of this spring allowed for the development of a model which attempts to recreate the discharge conditions observed. Along with groundwater recharge, other processes added to the model include evapotranspiration, storage, interflow spring outflow and groundwater outflow. Several different model simulation scenarios provided valuable insight into the greater groundwater dynamics. In terms of groundwater quality, nine borehole samples and one spring sample were analysed for major ions (Ca, Na, K, Cl, Mg, SO4, HCO3), metals (Cu, Fe, Mn) as well as pH and electrical conductivity. Overall electrical conductivity levels and major ion concentrations were lower in the Witpoort aquifer indicating a better groundwater quality compared to that of the Dwyka aquifer. Of the three metals included in the analysis, Mn proved to be the most significant and the highest concentrations were produced for samples that intersected the shale aquitard unit, suggesting that Mn-containing groundwater is drawn from this geological layer. Development of a supplementary and/or emergency groundwater supply requires careful consideration of the geology, quantity, quality, and recharge in the study site. All these aspects were assessed as well as deliberation into the potential infrastructural costs involved. Through conceptualisation of the system; evidence gathered during basic monitoring; and a simple spring model, the current study aimed to explore certain management strategies and recommend potential options going forward. The hidden nature of the resource together with the heterogeneity of fracture networks creates an inevitable uncertainty surrounding the system. Proper development and management of the aquifer can only be achieved if the system is continually monitored, modelled and utilised sustainably.
- Format
- 142 pages, pdf
- Publisher
- Rhodes University, Faculty of Science, Institute for Water Research
- Language
- English
- Rights
- Smetherham, Kyle Norman
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Collections
RU Institute for Water Research, including the Unilever Centre for Environmental Water Quality (IWR)
| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | SOURCE1 | SMETHERHAM-MSc-TR19-137.pdf | 5 MB | Adobe Acrobat PDF | View Details Download |