A hydrogeological investigation of Grahamstown, assessing both the dynamics and quality of the local groundwater system
- Authors: Smetherham, Kyle Norman
- Date: 2019
- Subjects: Hydrogeology -- South Africa -- Makhanda , Water quality -- South Africa -- Makhanda , Groundwater -- Quality -- South Africa -- Makhanda
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/94444 , 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.
- Full Text:
- Date Issued: 2019
- Authors: Smetherham, Kyle Norman
- Date: 2019
- Subjects: Hydrogeology -- South Africa -- Makhanda , Water quality -- South Africa -- Makhanda , Groundwater -- Quality -- South Africa -- Makhanda
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/94444 , 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.
- Full Text:
- Date Issued: 2019
The ecological impacts of pollution on a river ecosystem: a community index and stable isotope approach
- Authors: Gininda, Simphiwe Linah
- Date: 2017
- Subjects: Water -- Pollution -- Bloukrans River , Water quality -- South Africa -- Makhanda , Stream ecology -- South Africa -- Makhanda , South African Scoring System , Sewage disposal in rivers, lakes, etc. -- South Africa -- Makhanda , Agricultural ecology -- South Africa -- Makhanda , Agricultural pollution -- South Africa -- Makhanda
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/7993 , vital:21331
- Description: For decades, urbanized rivers have been modified to meet the needs of constantly expanding human populations in many countries around the world. The Bloukrans River in Grahamstown is one of the polluted and structurally modified urban rivers in South Africa, and there is no published information regarding its water quality and ecological status. Water quality is threatened by human activities including the disposal of treated and raw sewage, livestock farming, and agriculture. This study was conducted to determine the ecological status of the river by assessing its biological, chemical, and physical components in relation to man-mediated activities. Biological responses of macroinvertebrates were used to assess changes in water quality through space and time based on the South African Scoring System version 5 and the Average Score per Taxon water quality indices. The results showed poor water quality due to high nitrate and ammonium concentrations derived from sewage, and channel modifications by agricultural activities and dumping of solid waste. Channel width, water depth, dissolved oxygen, nitrate, and ammonium concentrations were the main drivers of macroinvertebrate distribution patterns and had the most influence on the variability in macroinvertebrates taxa richness, diversity and abundance. Diatoms were also used to assess water quality, specifically to indicate the trophic status of the river based on changes in the Trophic Diatom Index. The results suggested that the Bloukrans River was eutrophic during the course of this study. However, the trophic status varied with freshwater input, resulting in mesotrophic conditions during flooding and eutrophication in dry seasons. Changes in pH, phosphate concentration, water velocity (current speed), and temperature influenced the distribution of diatoms in the Bloukrans River. However, only pH was important at the community level and significantly influenced diatom abundances. Stable nitrogen isotope ratios (S15N) of autotrophs and primary and secondary consumers revealed noticeable differences between tissues of organisms exposed to treated sewage and those without any exposure. The S15N values in biota occurring above the sewage treatment discharge point were low, and those collected below the sewage point were higher. Although fertilizer derived nitrogen is generally depleted in 15N, agriculture-derived nitrogen could not be excluded as a possible source since animals at the sample site that was most affected by agricultural activities had the highest S15N values. This study provided valuable information on the ecological status of the Bloukrans River and identified the major activities associated with reduced biodiversity and water quality.
- Full Text:
- Date Issued: 2017
- Authors: Gininda, Simphiwe Linah
- Date: 2017
- Subjects: Water -- Pollution -- Bloukrans River , Water quality -- South Africa -- Makhanda , Stream ecology -- South Africa -- Makhanda , South African Scoring System , Sewage disposal in rivers, lakes, etc. -- South Africa -- Makhanda , Agricultural ecology -- South Africa -- Makhanda , Agricultural pollution -- South Africa -- Makhanda
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/7993 , vital:21331
- Description: For decades, urbanized rivers have been modified to meet the needs of constantly expanding human populations in many countries around the world. The Bloukrans River in Grahamstown is one of the polluted and structurally modified urban rivers in South Africa, and there is no published information regarding its water quality and ecological status. Water quality is threatened by human activities including the disposal of treated and raw sewage, livestock farming, and agriculture. This study was conducted to determine the ecological status of the river by assessing its biological, chemical, and physical components in relation to man-mediated activities. Biological responses of macroinvertebrates were used to assess changes in water quality through space and time based on the South African Scoring System version 5 and the Average Score per Taxon water quality indices. The results showed poor water quality due to high nitrate and ammonium concentrations derived from sewage, and channel modifications by agricultural activities and dumping of solid waste. Channel width, water depth, dissolved oxygen, nitrate, and ammonium concentrations were the main drivers of macroinvertebrate distribution patterns and had the most influence on the variability in macroinvertebrates taxa richness, diversity and abundance. Diatoms were also used to assess water quality, specifically to indicate the trophic status of the river based on changes in the Trophic Diatom Index. The results suggested that the Bloukrans River was eutrophic during the course of this study. However, the trophic status varied with freshwater input, resulting in mesotrophic conditions during flooding and eutrophication in dry seasons. Changes in pH, phosphate concentration, water velocity (current speed), and temperature influenced the distribution of diatoms in the Bloukrans River. However, only pH was important at the community level and significantly influenced diatom abundances. Stable nitrogen isotope ratios (S15N) of autotrophs and primary and secondary consumers revealed noticeable differences between tissues of organisms exposed to treated sewage and those without any exposure. The S15N values in biota occurring above the sewage treatment discharge point were low, and those collected below the sewage point were higher. Although fertilizer derived nitrogen is generally depleted in 15N, agriculture-derived nitrogen could not be excluded as a possible source since animals at the sample site that was most affected by agricultural activities had the highest S15N values. This study provided valuable information on the ecological status of the Bloukrans River and identified the major activities associated with reduced biodiversity and water quality.
- Full Text:
- Date Issued: 2017
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