The assessment of degradation state in Ecological Infrastructure and prioritisation for rehabilitation and drought mitigation in the Tsitsa River Catchment
- Authors: Mahlaba, Bawinile
- Date: 2022-04-06
- Subjects: Environmental degradation South Africa Eastern Cape , Restoration ecology South Africa Eastern Cape , Climate change mitigation South Africa Eastern Cape , Droughts South Africa Eastern Cape , South African National Biodiversity Institute , Sustainable development South Africa Eastern Cape , Watersheds , Ecological Infrastructure (EI) , Tsitsa River Catchment
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/202138 , vital:46470
- Description: Ecosystem degradation is a serious concern globally, including in South Africa, because of the potential adverse impacts on food security, livelihoods, climate change, biodiversity, and ecosystem services. Ecosystem degradation can result in flow alteration in the landscape through changes in the hydrological regime. The study adopts the South African National Biodiversity Institute (SANBI) Framework of Investing in Ecological Infrastructure (EI) to prioritise the restoration of degraded ecosystems and maintain ecosystem structures and functions. This study aims to assess how EI (specifically wetlands, grassland, abandoned cultivated fields, and riparian zone) can facilitate drought mitigation: to assess land degradation status and identify priority EI areas that can be restored to improve the drought mitigation capacity. Two assessment methods were used in this study. Firstly, the Trends.Earth tool was used to assess degradation and land cover change from the year 2000-2015 in Tsitsa catchment, through assessment of Sustainable Development Goal degradation indicator (SDG15.3.1) at a resolution of 300 m. The degradation indicator uses information from three sub-indicators: Productivity, Landcover and Soil Organic Carbon to compute degraded areas. The degraded areas need to be restored and rehabilitated to maintain the flow of essential ecosystems services provided by EI. The second assessment used the Analytical Hierarchy Process (AHP), which integrates stakeholder inputs into a multi-criteria decision analysis (MCDA). The AHP is a useful decision support system that considers a range of quantitative and qualitative alternatives in making a final decision to solve complex problems. As part of the AHP analysis, participatory mapping using Participatory Geographic Information System was conducted to obtain stakeholder inputs for prioritising restoration of the key EI categories (wetlands, grassland, abandoned cultivated fields, and riparian zone) in the catchment. During the participatory mapping, communities prioritised the key EI based on three criteria: (1) ecosystem health, (2) water provisioning and (3) social benefits. The AHP method was used in ArcGIS to prioritise suitable key EI restoration areas with high potential to increase water recharge and storage, contribute to drought mitigation and ecosystem services for the catchment. The prioritisation of EI for community livelihoods in the AHP analysis included all three main criteria. In comparison, the prioritisation of suitable key EI restoration areas for flow regulations was based on two criteria: ecosystem health and water provisioning. The land degradation indicator showed that approximately 54% of the catchment is stable, 41% is degraded land, and 5% of the area has improved over the assessment period (15 years). The degradation status in the EI suggests that more than half (>50%) of each EI category is stable, but there are areas showing signs of degradation, including 43% of grasslands degraded and 39% of wetlands, cultivated lands, and riparian zones also degraded. Degradation is dominant in the upper (T35B and T3C) and lower (T35K, T35L and T35M) parts of the catchments. The three criteria used by the stakeholders in the prioritisation process of the key EI were assigned 12 spatial attributes (the catchment characteristics about the study area in relation to the criteria) to indicate relevant information needed for selecting suitable restoration areas to enhance flow regulation. The AHP analysis results identified approximately 63% (17,703 ha) of wetlands, 88% (235,829 ha) of grasslands, 78% (13,608 ha) of abandoned cultivated fields and 93% (3,791 ha) of the riparian zones as suitable areas for restoration to mitigate drought impact through flow regulation. Also, the suitability results showed 63% (17,703 ha) of wetlands, 58% (2,203 ha) of riparian zones, 68% (11,745 ha) of abandoned cultivated fields and 46% (122,285 ha) of grasslands as suitable restoration areas for improving ecosystem services for community livelihoods. The AHP analysis identified more than 39-43% (of the degraded EI indicated by the Trends.Earth analysis) areas that are suitable for restoration, because key EI plays a significant role in flow regulation and people’s livelihoods, especially when they are managed, maintained, and restored to good health conditions. Therefore, the prioritized EI areas should be either maintained, managed, rehabilitated or restored. The major distinct causes of land degradation are woody encroachment in grasslands, invasion of alien plants on abandoned cultivated fields and soil erosion in the catchment. The most suitable EI areas recommended for restoration are those natural resources near local communities, which provide essential ecosystem services to sustain their livelihood. Therefore, degraded EI in the T35 catchments should be restored and maintained to improve livelihood and mitigate drought impacts. The study pointed out how the key selected ecological infrastructure can help mitigate the impacts of droughts and improve human livelihood. The study contributes towards the important concept of investing in ecological infrastructure to improve the social, environmental, and economic benefits. , Thesis (MSc) -- Faculty of Science, Institute for Water Research, 2022
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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.
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Determining the hydrological functioning of the palmiet wetlands in the Eastern and Western Cape South Africa
- Authors: Smith, Caitlin
- Date: 2019
- Subjects: Wetlands -- South Africa -- Eastern Cape , Wetland ecology -- South Africa -- Eastern Cape , Wetland management -- South Africa -- Eastern Cape , Prioniaceae -- South Africa -- Eastern Cape , Prionium serratum -- South Africa -- Eastern Cape
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/95956 , vital:31218
- Description: Wetlands provide a range of supporting, regulating and provisioning ecosystem services, including hydrological benefits such as flood attenuation and sustaining base flows. Despite their value, wetlands are one of the most vulnerable ecosystems in South Africa. Palmiet wetlands in the Eastern and Western Cape are particularly threatened. Palmiet (Prionium serratum) is a robust perennial plant that is endemic to wetlands and rivers located in the sandstones and quartzites of the Table Mountain Group (TMG), in the Eastern and Western Cape as well as the Natal Group sandstones in KwaZulu-Natal. Palmiet is described as an ecosystem engineer because of its ability to alter its environment and create large valley-bottom wetlands. The Krom River is an important water source for the city of Port Elizabeth and there has been a decline in palmiet wetlands along the Krom River as a result of alien vegetation invasion, agricultural activity, and gully erosion. Working for Water has been clearing alien vegetation and Working for Wetlands has been installing rehabilitation structures in the Krom River catchment for a number of years. There are, however, serious knowledge gaps in the understanding of palmiet wetland structure and function, particularly in respect of the hydrological functioning of these wetland systems. The aim of this study was to investigate the hydrology (surface and groundwater) behind these wetland systems. The investigation focussed on small-scale dynamics of the palmiet wetland system in order to increase general understanding of the surface water and groundwater processes of these wetland systems. Field work was concentrated on the Kompanjiesdrif and Krugersland palmiet wetlands in the upper K90A Krom River catchment. The investigation involved the installation of piezometers, water quality and stable isotope sampling and analysis, an Electrical Resistivity Tomography survey, and hydrological and mixing cell modelling. The results of the investigation indicate that the hydrological functioning of palmiet wetlands is closely linked with high sub-surface discharges typically associated with TMG aquifers. It is proposed that the palmiet wetlands are sustained by significant amounts of sub-surface water (both groundwater and interflow) moving through preferential flow paths in the alluvial fans and tributaries, which are in turn sustained by groundwater discharge from the surrounding sandstones and quartzites of the Nardouw Sub-group and Peninsula Formation. The palmiet wetlands clearly retain a significant amount of water, leading to the maintenance of prolonged flows, and a larger baseflow. However, it is hypothesised that the occurrence of palmiet as the dominant species in these wetlands is due to the sustained low flows related to catchment geology and high hydrological connectivity between the catchment and the wetland that is enabled by flow paths that allow the free flow of water from the catchment to the wetland. It is further proposed that palmiet is possibly more reliant on a consistent water supply for its existence and survival than it is on acidic nutrient-poor water and soils as stated by other authors.
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