A comparison of the legal environmental sustainability requirements of those engaging in the mining cycle, with actual practice in the Carolina X11B quaternary catchment, Mpumalanga, South Africa
- Authors: Thomson, Gareth Peter
- Date: 2018
- Subjects: Mineral industries Environmental aspects South Africa Mpumalanga , Acid mine drainage , Mineral industries Safety measures , Watersheds South Africa , South Africa. National Environmental Management Act, 1998 , Water-supply Law and legislation South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/63481 , vital:28417
- Description: Mining is one of the most contentious water users. The mining sector has assumed that promises of economic growth and job creation will enable environmental concerns to be bypassed with as little interference as possible. More recently, the reality of legacy issues related to the inappropriate sign-off of mining sites has become increasingly clear, with acid mine drainage (AMD) being a prime example. There are also increasing concerns regarding uncontrolled prospecting. Climate change is one of the major issues faced in the 21st century, with predictions of heightened water stress for the Southern African region. This, coupled with increased population growth is putting a massive strain on the water resources currently available, making it vital to better protect and ensure the longevity of our water resources. The Carolina Crisis of 2012 highlighted the importance of protecting our water resources, and how easily they can be contaminated to a point where water is not usable. The Carolina crisis provided researchers with a suitable study site to better understand the role mining operations have in a catchment that has experienced a major pollution incident, and what changes have occurred since. In order to understand coal mining practice in relation to regulatory provisions, this project critically explored the processes involved within the mining sector, from ‘cradle-to-grave’, which is known as the coal mining life cycle. In addition, the composite suite of requirements of all the legislative provisions involved in the industry were investigated and the relationship between coal mining practice and environmental protection was explored. These elements were researched in the Upper Komati River Catchment specifically for catchment X11B, using Cultural Historical Activity Theory (CHAT), which gives a holistic understanding of mining as a human activity system. CHAT also sheds light on the issues, gaps and overlaps currently being experienced in the coal mining sector. The Thesis refers to case studies of where mining issues have caused environmental degradation. A complete mining lifecycle in terms of regulatory provisions was compiled, and major issues were uncovered with current legislation in the mining sector that can contribute to the degradation of water resources in South Africa. An integrated water resource quality management plan is needed in order to streamline conservation mandates, identify and reduce duplication of effort and specify roles and responsibilities of authorities involved with decision making process. A Decision Support System (DSS) has been proposed, which would involve adaptive, participatory and inclusive management.
- Full Text:
- Date Issued: 2018
Macroinvertebrate and diatom assemblage responses to pollution, with emphasis on salinity, in the Kat River, Eastern Cape South Africa
- Authors: Mgaba, Ntombekhaya
- Date: 2018
- Subjects: Water -- Pollution -- South Africa -- Kat River , Stream salinity -- South Africa -- Kat River , Sewage disposal plants -- South Africa , Environmental monitoring -- South Africa -- Kat River , Water quality -- South Africa -- Kat River , South African Scoring System version 5 (SASS5) , Macroinvertebrate Response Assessment Index (MIRAI)
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/63279 , vital:28389
- Description: Salinity has been implicated as one of the major contributors to deteriorating water quality of freshwater ecosystems around the globe. In South Africa, anthropogenic activities such as mining, agriculture, industry and wastewater treatment works (WWTWs) are the major sources of increasing salinity levels of freshwater resources. The main focus of this study was to assess the impact of salinity on water quality of the Kat River using macroinvertebrates and diatoms as bioindicators. Biomonitoring using macroinvertebrates and diatom communities and concurrent sampling of water physicochemical variables were conducted bi-monthly from December 2015 to November 2016.This period covered summer and winter, and the study was conducted at five selected sites (Sites 1, 2, 3, 4 and 5) along the length of the Kat River. For macroinvertebrates biomonitoring, the South African Scoring System version 5 (SASS5) and Macroinvertebrate Response Assessment Index (MIRAI) were applied to collect and analyse data, while the Taylor et al (2006) protocol for collecting and analysing diatom assemblages was modified and used for diatom collection and analysis. Water physicochemical variables, including hydrogen ion concentration (pH), electrical conductivity (EC), dissolved oxygen (DO), temperature, turbidity and stream flow were determined in situ using appropriate multiprobe meter and/or techniques. Nutrients (NO3-N, NO2-N, NH4-N and PO4-P) were analysed in the laboratory using appropriate analytical methods. All data were subjected to appropriate statistical analyses and statistical decisions were made at an alpha value of 0.05. Particularly, multivariate analyses of both macroinvertebrates and diatoms assemblages were conducted using canonical correspondence analysis and Bray-Curtis similarity analysis, while indicator species analysis was used to determine which species is/are more significant with respect to biomonitoring in the Kat River. Biotic diversity indices were also measured and used to discriminate between least and most impacted sites. The Kat River water quality was found to have experienced a varying degree of modification compared to Generic Resources Water Quality Objectives limits. Change in DO, stream flow, EC, nutrients and turbidity exerted the greatest influenced on the macroinvertebrates assemblage structure, with organisms at Sites 4 and 5 (downstream sites) showing more significant negative impact compared to organisms at Sites 1, 2 and 3 (upstream sites). Analysis of the diatom biomonitoring showed more negative impact at Sites 2, 4 and 5 compared to Sites 1 and 3. Fort Beaufort Wastewater Treatment Works and small-scale farming activities, as well as leaking of pipes carrying sewage, were found to be the likely major sources of anthropogenic activities responsible for the observed increased salinity and other pollutants in the Kat River. Overall, this study found macroinvertebrates (identified up to the family level) as good for biomonitoring to assess or predict water quality of the Kat River, while diatoms were found to be most suitable for biomonitoring to assess salinity in the Kat River.
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- Date Issued: 2018
Mining, agriculture and wetland ecological infrastructure in the Upper Komati catchment (South Africa): contestations in a complex social-ecological system
- Authors: Keighley, Tia-Kristi
- Date: 2018
- Subjects: Wetland ecology -- Komati River Watershed , Coal mines and mining -- Environmental aspects -- Komati River Watershed , Agriculture -- Environmental aspects -- Komati River Watershed , Acid mine drainage -- Komati River Watershed , Water quality -- Physiological effect -- Komati River Watershed , Wetland conservation -- Komati River Watershed , National Freshwater Ecosystem Priority Areas (NFEPAs)
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/63810 , vital:28491
- Description: Wetlands provide a wide variety of natural benefits (ecosystem services) from the natural environment to human populations, making them key examples of ecological infrastructure. However, the use of wetlands and their associated catchments is often contested by different users, making them nodes of conflict. Thus, there is a range of pressures on many wetlands which can ultimately lead to degradation or destruction. This study investigated the X11B quaternary catchment in the Upper Inkomati basin, Mpumalanga, South Africa. This catchment is characterised by a network of wetlands and streams that provide catchment residents with water. The sub-catchment is heavily used, dominated by the agricultural sector and coal mining. To understand the contestation, a contextual analysis was carried out. Selected wetland conditions and ecosystem services, along with user perceptions and the value of wetland-use, were assessed. Wetlands were observably in a relatively healthy condition. The resilience of wetlands and the efficiency of the ecosystem services they offer, especially in mediating water quality, were clear. The early results indicated a healthy landscape despite multiple-user impact from human activity. The health scores and provision of ecosystem services, along with the identified National Freshwater Ecosystem Priority Areas (NFEPAs) and red-listed fauna and flora, provide a substantial grounding for advocating the conservation of the wetlands of the contested X11B catchment. When water quality measures were added to the wetland health and ecosystem service assessment, low pH levels and high electrical conductivity were recorded. Both measures indicate coal mining impacts, more specifically Acid Mine Drainage (AMD) impacts, since AMD typically has sulphate as the dominant salt ion, and high concentrations of trace elements and metal ions. Concentrations breaching the recommended resource quality objectives (RQOs) of trace elements and ions, found in fertilizers and pesticides, were recorded in most sites, suggesting agricultural impacts on the landscape’s hydrology. Further, these agricultural impacts would add to the compromising effect of the wetlands’ capacity to remove pollutants from the water body. Livestock farming on all sites were also near wetlands which may have limited the vegetation cover of grazed land, so increasing runoff and the volume of water entering wetlands and compromising their ecosystem services. Poor water quality has implications for biophysical processes, which play an important role in the functioning of wetlands, for the benefit of users. Without the water quality measures, ecosystem health and ecosystem service methodology used suggested a healthy catchment. However, simple field water quality measures indicated past and present mining impacts. Therefore, the mandatory use of water chemistry is recommended in the assessment of wetlands in catchments with past and present mining activity taking place. Without this, repercussions would include wetland loss, and a more thorough investigation into the water quality and its effects on the wetland ecosystems is suggested. Further ecological investigation of water chemistry (heavy metals, ions, nutrients and trace elements) and macroinvertebrate assemblages identified links to water chemistry impacts on macroinvertebrate abundance and diversity. Abundance results based on the presence, absence and abundance of macroinvertebrates at the different sites did not reveal any clear patterns associated with different landscape users. Diversity, on the other hand, was related to land-use, where sites with high mining use had lower macroinvertebrate diversity than other sites. Related, concurrent, hydro-pedology research produced a more comprehensive understanding of the impact of mining on hydro-connectivity that clearly indicates mining as the cause of long-term deterioration of functional wetland health in a way that is practically impossible to restore. This study suggests that wetlands provide a strong ecosystem service of intermittent resetting of the wetland sediment adsorptive capacity for toxic metal and other salt ions. The hypothesis arising from the work is that, in the case of another heavy rainfall event, the town of Carolina risks another AMD crisis. As sediments are likely to be accumulating and saturated with toxic metal ions. Further AMD-related changes in acidity will increase the mobilisation of adsorbed ions. Future flooding and flushing of wetlands will therefore once again move toxic metal ions through the system, and possibly re-contaminate the Boesmanspruit dam. The value of the study is in delivering specific evidence on the impacts of mining (and to a lesser extent agriculture) on wetland quality. Overall, this study, combined with additional research, indicates that in the X11B catchment, mining impacts are long-term and more serious than agriculture. In terms of contestation the research indicates that reliance on bio-physical data and knowledge is inadequate in resolving conflict between coal mining and other land- and water-users. The study demonstrates the necessity of insight into the social system and the value of a transdisciplinary approach in addressing land-use conflicts and wetland protection.
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- Date Issued: 2018
Modelling plant water use of the grassland and thicket biomes in the Eastern Cape, South Africa: towards an improved understanding of the impact of invasive alien plants on soil chemistry, biomass production and evapotranspiration
- Authors: Gwate, Onalenna
- Date: 2018
- Subjects: Grasslands -- South Africa -- Eastern Cape , Invasive plants -- South Africa -- Eastern Cape , Rangelands -- South Africa -- Eastern Cape , Range ecology-- South Africa -- Eastern Cape , Rangelands -- Water-supply , Rangelands -- Weed control , Evapotranspiration , Plant-water relationships
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/54800 , vital:26617
- Description: It is imperative to understand the strong coupling between the carbon capture process and water use to sustainably manage rangelands. Woody encroachment is undermining rangelands grass production. Evapotranspiration (ET) highlights the links between ecosystem carbon capture process and water use. It forms the biggest flux of the hydrological cycle after precipitation yet it is not well understood. The Grassland and the Albany Thicket (AT) biomes in the Eastern Cape, South Africa, provide an interesting space to study the dynamics in rangelands biomass production and the associated water use. Therefore, the main purpose of this study was to contribute towards management of rangelands by understanding the dynamics in rangeland grass production and water use. To achieve this aim, the impact of Acacia mearnsii, an invasive alien plant, on soil chemical properties and rangelands grass production was investigated. This was achieved by analysing the biophysical attributes of A. mearnsii as they related to grass production. Secondly, selected soil variables that could be used as a prognosis for landscape recovery or deterioration were evaluated. In addition, aboveground grass biomass was measured in areas cleared of A. mearnsii and regression equations were prepared to help model aboveground grass biomass in areas cleared of A. mearnsi. The thesis also explored dynamics in water vapour and energy fluxes in these two biomes using an eddy covariance system. Consequently, water vapour and energy fluxes were evaluated in order to understand landscape water use and energy partitioning in the landscape. The study also tested the application of Penman-Monteith equation based algorithms for estimating ET with micrometeorological techniques used for validation. Pursuant to this, the Penman- Monteith-Leuning (PML) and Penman-Monteith-Palmer (PMP) equations were applied. In addition, some effort was devoted to improving the estimates of ET from the PMP by incorporating a direct soil evaporation component. Finally, the influence of local changes in catchment characteristics on ET was explored through the application of a variant of the Budyko framework and investigating dynamics in the evaporative index as well as applying tests for trends and shifts on ET and rainfall data to detect changes in mean quaternary catchment rainfall and ET. Results revealed that A. mearnsii affected soil chemical properties and impaired grass production in rangelands. Hence, thinning of canopies provided an optimal solution for enhanced landscape water use to sequestrate carbon, provide shade, grazing, and also wood fuel. It was also shown that across sites, ET was water limited since differences between reference ET and actual ET were large. ET was largely sensitive to vapour pressure deficit and surface conductance than to net radiation, indicating that the canopies were strongly coupled with the boundary layer. Rangeland ET was successfully simulated and evaporation from the soil was the dominant flux, hence there is scope for reducing the so-called ‘unproductive’ water use. Further, it was shown that the PML was better able to simulate ET compared to the PMP model as revealed by different model evaluation metrics such as the root mean square error, absolute mean square error and the root mean square observations standard deviation ratio. The incorporation of a soil evaporation component in the PMP model improved estimates of ET as revealed by the root mean square error. The results also indicated that both the catchment parameter (w) and the evaporative index were important in highlighting the impacts of land cover change on ET. It was also shown that, despite changes in the local environment such as catchment characteristics, global forces also affected ET at a local scale. Overall, the study demonstrated that combining remote sensing and ground based observations was important to better understand rangeland grass production and water use dynamics.
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- Date Issued: 2018
Quantification of water resources uncertainties in two sub-basins of the Limpopo River basin
- Authors: Oosthuizen, Nadia
- Date: 2018
- Subjects: Hydrologic models -- Limpopo River Watershed , Water-supply -- Limpopo River Watershed , Water-supply -- Management , Sustainable development , Rain and rainfall -- Mathematical models , Runoff -- Mathematical models , Reservoirs -- Limpopo River Watershed
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/63267 , vital:28388
- Description: The demand for water is rapidly growing, placing more strain on access to the resources and subsequently its management. For sustainable management, there is a need to accurately quantify the available water resources. Unfortunately, the data required for such assessments are frequently far from sufficient in terms of availability and quality, especially in southern Africa. In the absence of historical observed data, models are generally used to describe the different hydrological processes and generate data and information that will inform management and policy decision making. Ideally, any hydrological model should be based on a sound conceptual understanding of the processes in the basin and be backed by quantitative information for the parameterization of the model. Such data is however, often inadequate in many sub-basins necessitating the incorporation of the uncertainty related to the estimation process. Model parameter estimation and input data are significant sources of uncertainty that should be quantified. Also, in southern Africa water use data are unreliable because available databases consist of licensed information and actual use is generally unknown. In this study, the water resources of two sub-basins of the Limpopo River basin – the Mogalakwena in South Africa and the Shashe shared between Botswana and Zimbabwe – are estimated. The study assessed how uncertainties in the Pitman model parameterisation and input water use data affect the estimation of surface water resources of the selected sub-basins. Farm reservoirs and irrigated areas data from various sources were collected and used to run the Pitman model. Results indicate that the total model output uncertainty is higher for the Shashe sub-basin which is more data scarce than the Mogalakwena sub-basin. The study illustrates the importance of including uncertainty in the water resources assessment process to provide baseline data for decision making in resource management and planning. The study reviews existing information sources associated with the quantification of water balance components and gives an update of water resources of the sub-basin. The flows generated by the model at the outlet of the basin were between 22.6 Mm3 and 24.7 Mm3 per month when incorporating uncertainty to the main physical runoff generating parameters. The total predictive uncertainty of the model increased to between 22.2 Mm3 and 25.0 Mm3 when anthropogenic water use data such as small farm and large reservoirs and irrigation were included. The flows generated for Shashe was between 11.7 Mm3 and 14.5 Mm3 per month when incorporating uncertainty to the main physical runoff generating parameters. The predictive uncertainty of the model changed to 11.7 Mm3 and 17.7 Mm3 after the water use uncertainty was added. However, it is expected that the uncertainty could be reduced by using higher resolution remote sensing imagery.
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- Date Issued: 2018
The ecological risk of acid mine drainage in a salinising landscape
- Authors: Vellemu, Emmanuel Captain
- Date: 2018
- Subjects: Acid mine drainage Environmental aspects South Africa Mpumalanga , Salinization South Africa Mpumalanga , Water salinization South Africa Mpumalanga , Water quality South Africa Mpumalanga , Aquatic animals Effect of water quality on South Africa Mpumalanga , Freshwater ecology South Africa Mpumalanga
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/60563 , vital:27797
- Description: Acid mine drainage (AMD) and increasing salinity of freshwater ecosystems pose serious threats to water quality in water-stressed South Africa. These threats are exacerbated by mining activities, mainly gold and coal from both active and abandoned mines that continue to release acidic water that is rich in toxic metals and high sulphate concentrations. Therefore, the overarching hypothesis for this study was that “the combination of AMD and sulphate salts confers high ecological risk to the aquatic biota”. The study employed both laboratory and field investigations to test this hypothesis and provide appropriate tools to protect freshwater ecosystems from increasing anthropogenic impacts. Firstly, a laboratory investigation was carried out to develop risk-based water quality guidelines (WQGs) for sulphates and treated AMD (TAMD) using the species sensitivity distributions (SSDs) technique. Five South African freshwater species belonging to five different taxonomic groupings, including Adenophlebia auriculata (insect), Burnupia stenochorias (mollusc), Caridina nilotica (crustacea), Pseudokirchneriella subcapitata (algae) and Oreochromis mossambicus (fish) were exposed to varying concentrations of sodium sulphate (Na2SO4), magnesium sulphate (MgSO4) and calcium sulphate (CaSO4), as well as TAMD in separate ecotoxicological experiments, applying short-term (96 h) non-renewal and long-term (240 h) renewal exposure test methods. Secondly, a novel trait-based approach (TBA) was also used to predict the vulnerability of taxa to treated acid mine drainage (TAMD). The TBA used a combination of carefully selected traits of organisms that are mechanistically linked to TAMD for their potential vulnerability predictions. Leptoceridae (caddisflies) and Leptophlebiidae (mayflies) were selected taxa for evaluation of the trait-based vulnerability predictions to TAMD for laboratory toxicity exposures. This was followed by a field investigation to assess macroinvertebrates assemblage responses, abundance and richness to a TAMD-impacted stream using the South African Scoring System version 5 (SASS5) protocol. Outcomes form the above three sources were combined in a multi-criteria analysis (MCA) to develop an appropriate water quality management strategy in a form of a trait-based decision-making support tool. Results of the risk-based WQGs revealed that Na2SO4 was the most toxic of the tested salts. A concentration of 0.020 g/L Na2SO4, 0.055 g/L CaSO4, and 0.108 g/L MgSO4 or a combined sulphate salts limit of 0.067 g/L were derived as long-term WQGs to protect over 95% of the population species in a natural environment considered as relatively pristine. This means that the generic 0.25 g/L sulphate compliance limit for South African freshwater systems is under-protective. Burnupia stenochorias was the most sensitive to AMD after long-term exposures, and it was adjudged as a good indicator of AMD along with P. subcapitata. Long-term scenario-specific WQG for AMD for the protection of over 95% of the population species was derived as 0.014%. Results of the TBA revealed that the relative abundance and diversity of taxa at a site that received direct impact from TAMD generally corresponded to trait-based predictions. The site that received direct TAMD was largely dominated by members of the Corixidae and Naucoridae families. However, Leptoceridae was more vulnerable to TAMD than Leptophlebidae contrary to predictions. Its assemblage did not match the predictions although Leptophlebiidae corresponded to predictions in terms of its assemblage and diversity. As water quality improved further downstream of the TAMD source, macroinvertebrates assemblage and diversity also improved as predicted. However, it is important to note that other equally important traits that were not studied might influence the response of organisms during toxicity test exposures. The MCA findings suggest that the trait-based decision-making support tool is a useful management strategy for the predicting vulnerability of taxa aquatic stressors including AMD and increasing salinity. Overall, the outcome of this study suggests that AMD poses an ecological risk to aquatic biota, but this becomes riskier in the presence of excess sulphate salts. Albeit, the WQGs for sulphate salts and AMD as well as the developed trait-based decision support tool all contribute novel sound scientific knowledge basis for managing the AMD and increasing salinity in freshwater ecosystems. The study recommends incorporating different life stages of indigenous species tested to determine if their sensitivity to AMD and sulphate would correspond to current findings because early life stages could be more sensitive to aquatic stressors than juveniles or adults. This is important for the derivation of strong and relevant WQGs. The TBA requires further refinement for its incorporation in ecotoxicology on a wide scale.
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- Date Issued: 2018
Understanding and quantifying channel transmission loss processes in the Limpopo River Basin
- Authors: Mvandaba, Vuyelwa
- Date: 2018
- Subjects: Water-supply -- Management , Water-supply -- Limpopo River Watershed , Alluvium -- Limpopo River Watershed , Streamflow -- Limpopo River Watershed
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/63797 , vital:28490
- Description: Water availability is one of the major societal issues facing the world. The ability to understand and quantify the impact of key hydrological processes on the availability of water resources is therefore integral to ensuring equitable and sustainable resource management. A review of previous hydrological studies conducted in the Limpopo River Basin has revealed a gap in the understanding of surface water-groundwater interactions, particularly channel transmission loss processes. These earlier studies, focused largely on the Limpopo River’s main stem, have attributed the existence of these streamflow losses to the presence of significant alluvial aquifers and indicated that the losses account for about 30 percent (or 1000 Mm3 a-1) of the basin’s water balance. The work conducted in this dissertation reports on the delineation of alluvial aquifers across three sub-basins of the Limpopo River Basin namely, the Mokolo (South Africa), Motloutse (Botswana) and Mzingwane (Zimbabwe) sub-basins and the estimation of potential channel transmission losses based on the alluvial aquifer properties. Additionally, an assessment of the different approaches that can be applied to simulate these channel transmission losses in the Pitman Model is presented. To delineate alluvial aquifers, general land cover classes including alluvial aquifers were produced from Landsat-8 imagery through image classification. The areal extent of the delineated alluvial aquifers was calculated using ArcMap 10.3. To quantify channel transmission losses and determine the effects on regional water resources, three approaches using the Pitman model were applied. The three approaches include an explicit transmission loss function, the use of a wetland function to represent channel-floodplain storage exchanges and the use of a ‘dummy’ reservoir to represent floodplain storage and evapotranspiration losses. Results indicate that all three approaches were able to simulate channel transmission losses, although with differing magnitudes. Observed monthly flow data were used to as a means of validating loss simulations however for each sub-basin, medium and low flows were over-simulated which accounts for water uses that were inefficiently represented due to lack of data. Knowledge of the structure of the transmission loss function dictates that it is better at representing the dynamics of channel transmission losses, as it takes into account the contribution of losses to groundwater recharge whereas the other two functions simply store water and release it back to the channel. Overall, the hydrological modelling results demonstrate the potential of each approach in reproducing the dynamics of channel transmission losses between channel and alluvial aquifer within an existing sub-basin scale hydrological model. It is believed that better quantification of losses and more efficient qualitative determination of the function which best represents transmission losses, can be attained with more reliable observed data. In conclusion, a study of this nature can be beneficial to water resource estimation programmes as it highlights the uncertainties related with quantifying channel transmission loss processes in a semi-arid environment.
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- Date Issued: 2018
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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- Date Issued: 2019
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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- Date Issued: 2019
Investigating epistemic justice in an adaptive planning process: towards developing a local catchment management strategy
- Authors: Ralekhetla, Mateboho Mary
- Date: 2019
- Subjects: Watershed management -- South Africa , Watershed management -- South Africa -- Moral and ethical aspects , Water resources development -- South Africa -- Eastern Cape , Water-supply -- South Africa -- Makhanda , Makana Water Forum (Makhanda, South Africa) , Makana Municipality (Makhanda, South Africa)
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/95980 , vital:31220
- Description: In South Africa, Integrated Water Resource Management (IWRM) is being put into practice in a way that incorporates the belief that all stakeholders should be given a voice in decisions that affect them. Catchment Management Forums (CMFs) are the first place for stakeholder participation, supported by Catchment Management Agencies (CMAs). A key first task of a CMA is to develop of their Catchment Management Strategy (CMS). In this research, I consulted and worked with stakeholders in the Makana Water Forum (Makana Local Municipality, Eastern Cape, South Africa) throughout the process as they worked towards formulating their local CMS. Importantly, this study used insights from the community to focus on the inter- and intra-group interactions among the stakeholders who participated in the first step of Strategic Adaptive Planning. In the process, I explored epistemic contestations that occurred between different epistemic agents (participants) who may have held identity prejudices. The research aimed to allow voices, which could otherwise have been marginalised, to come out in ways that were not stigmatised through the written and personal reflective process. In doing this, the study tried to hear the voice of the oppressed speaker whose knowledge and lived experiences have been overlooked by the hearer’s prejudice. Findings show that participants who were part of the CMS development process experienced epistemic justice. These findings further established that the addition of participant reflections enhanced the level of epistemic justice promoted by the Adaptive Planning Process (APP).
- Full Text:
- Date Issued: 2019
Mapping and predicting potential distribution patterns of free-range livestock in the rural communal rangelands of Mgwalana, Eastern Cape, South Africa
- Authors: Mkabile, Qawekazi
- Date: 2019
- Subjects: Range management -- South Africa , Grazing -- South Africa , Livestock -- South Africa , Livestock -- Monitoring -- South Africa , Livestock -- Remote sensing -- South Africa , Communal rangelands -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/96000 , vital:31223
- Description: Communal rangelands provide habitat to many plants and animals. However, there is evidence that livestock cause range degradation. Range degradation occurs because livestock select grazing based on the availability of resources such as water and forage material, their use of the landscape is non-uniform, consequently causing resource deterioration. Range management is thus necessary because communities depend on range condition for livestock productivity. However, precise quantification of livestock distribution within communal rangelands is lacking. In developed countries, Global Positioning Systems (GPS) collars have been used to monitor wildlife and domestic livestock in pastures and seem to have worked efficiently. However, in a developing country like South Africa, GPS technology to monitor animal behaviour has been used only for wildlife on privately owned land. The high costs of monitoring livestock herds in large open areas such as communal rangelands have resulted in little or no monitoring of domestic livestock using GPS technology. This study links monitored livestock distribution to physical landscape variables in Mgwalana, and uses the modelled relationship to predict livestock distribution in quaternary catchments, T12A and T35A-E. The research addresses the questions (1) where do livestock spend time in the wet and dry seasons? And (2) how can areas of potential livestock distribution be identified in other catchments where actual distribution is unknown? Livestock were tracked during the wet and dry seasons using GPS collars. The resulting distribution data is combined with selected physical landscape variables to identify selectivity. The GPS location data and the physical landscape variables are used to predict potential livestock distribution where distribution is unknown in quaternary catchments (T12A and T35A-E). The ArcGIS Predictive Analysis Tool (PAT) was used to extract the selected landscape variable ranges based on the GPS location data and identify areas with the same conditions in the quaternary catchments were subsequently selected. The key findings are that livestock prefer accessible areas with gentle terrain near water sources, avoiding south-facing slopes which receive less solar radiation and tend to be cooler. Livestock are attracted to vegetation in riparian zones. Rural communal lands are dominated by poverty, and land-based livelihood strategies can potentially contribute to the well-being of the community. Therefore, understanding livestock distribution can contribute to a rangeland management strategy aimed at improving range condition which could increase livestock productivity and contribute to the livelihoods of local people.
- Full Text:
- Date Issued: 2019
Taxonomic and trait-based responses of the orders Ephemeroptera, Plecoptera, Odonata, And Trichoptera (EPOT) to sediment stress in the Tsitsa River and its tributaries, Eastern Cape, South Africa
- Authors: Akamagwuna, Frank Chukwuzuoke
- Date: 2019
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/68082 , vital:29196
- Description: Increased urbanization and industrialisation due to human population growth and associated high demand for food have led to widespread disturbances of freshwater ecosystems and associated resources. A widely recognised consequence of these disturbances is the excessive delivery of sediments into the freshwater ecosystems, which severely affects the functioning and integrity of these systems.. The major water quality impairment in the Tsitsa River and its tributaries, situated in the Mzimvubu catchment in the Eastern Cape Province of South Africa, is known to be excessive sediment input. In this study, the application of macroinvertebrates taxonomic-based and trait-based approaches was used to assess the responses and vulnerability of Ephemeroptera, Plecoptera, Odonata and Trichoptera (EPOT) species to settled and suspended sediments stress in eight selected sampling sites in the Tsitsa River and its tributaries. The eight selected sites were Site 1 (Tsitsa upstream), Site 2 (Tsitsa downstream), Site 3 (Qurana tributary), Site 4 (Pot River upstream), Site 5 (Pot River downstream), Site 6 (Little Pot River), Site 7 (Millstream upstream) and Site 8 (Millstream downstream). The methods used in this study involved the analysis of water physico-chemical variables as well as sediment characteristics, derivation of five EPOT metrics, EPOT species-level taxonomic analysis, individual EPOT trait analysis and the development of a novel trait-based approach using a combination of traits. The sampling of EPOT taxa was done using the SASS5 protocols. Identification of EPOT was done to genus/species level and all data were subjected to relevant statistical analysis. The results of ecological categories derived for the physico-chemical variables generally indicated the ecological categories A and B, which was indicative of good water quality conditions. The result of sediment particle analysis revealed four distinct site groups: site group 1 (Tsitsa River upstream and Qurana tributary), site group 2 (Tsitsa River downstream and Millstream upstream), site group 3 (Pot River, both upstream and downstream, and Millstream downstream) and site group 4 (Little Pot River). The species-level taxonomic analysis of EPOT revealed that site group 1 was the most sediment-influenced sites whereas site group 4 was the least sediment-influenced. Species such as Paragopmhus sp., Aeshna sp. and Baetis sp. were considered sediment-tolerant with strong positive association with site group 1. The novel trait-based approach developed in this study proved useful in predicting the responses of EPOT species to sediment stress, and further discriminated between the study sites. The approach was used to group EPOT species into four vulnerability classes. The result showed that filter feeding EPOT species that have filamentous gills, preferring stone biotopes and feeding on detritus (FPOM) were mostly classified as highly vulnerable to sediment stress and indicated no significant association with the highly sediment-influenced site group 1. The TBA largely corresponded well to the predictions made with the relative abundance of the vulnerable class decreasing in the sediment-influenced sites compared to the tolerant and highly tolerant classes. Overall, the study revealed the importance of the complementary use of taxonomic and trait-based approaches to biomonitoring.
- Full Text:
- Date Issued: 2019
Using a social-ecological systems approach to investigate hillslope seep wetlands ecosystem structure and functionality in the Tsitsa River catchment, Eastern Cape, South Africa
- Authors: Libala, Notiswa
- Date: 2019
- Subjects: Wetland management -- South Africa -- Eastern Cape , Wetland ecology -- South Africa -- Eastern Cape , Wetland conservation -- South Africa -- Eastern Cape , Slopes (Physical geography) -- South Africa -- Eastern Cape , Vegetation management -- South Africa -- Tsitsa River Catchment , Land degradation -- Control -- South Africa -- Tsitsa River Catchment , Grazing -- Environmental aspects -- South Africa -- Tsitsa River Catchment , Ecosystem management -- South Africa -- Tsitsa River Catchment , Wetland plants -- Effect of grazing on
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/115936 , vital:34270
- Description: Wetlands are critical ecosystems that can provide services of great social, economic and environmental value to the society. Yet, in South Africa, hillslope seep wetlands are among the most threatened ecosystems due to human-induced activities and are disappearing rapidly. Further, despite the potential vulnerability of hillslope seep wetland to disturbances, and their criticality in relation to all year round provision of forage for livestock grazing, they are among the most poorly studied wetland systems. Using a social-ecological system framing, and drawing on a range of ecological and social sciences methods, this study shed light on ways in which an integrative approach can contribute to sustainable utilisation of hillslope seep wetlands in the Tsitsa River catchment in the Eastern Cape province of South Africa. The study specific objectives were to i) evaluate the performance of Floristic Quality Assessment Index (FQAI), WET-Health and Floristic Assessment Quotient for Wetlands Index (FQAWet) indices for assessing hillslope seep wetlands ecological health ii) develop a trait-based approach for assessing the potential resilience and vulnerability of hillslope seep wetland plant species to disturbances, iii) assess the role of hillslope seep wetlands in the local communities in relation to livestock, and explore understanding of local people about the value of hillslope seep wetlands, iv) demonstrate collaborative insights emerging from an integrative social-ecological system research process to inform sustainable management of hillslope seep wetlands. A total of 11 hillslope seep wetlands were visually classified based on the level of erosion. Plant species composition within the wetlands was determined along a 100 m line transects across the hillslope wetland sites. 5 quadrats of 0.2m2 were also placed along transect for vegetation collection and cover. The plant species collected were used to calculate (FQAI) and FQAWet scores to evaluate the condition of hillslope seep wetlands. The degree of human disturbances was assessed using the Anthropogenic Activity Index (AAI), an index for qualitatively assessing the degree of human disturbance based on visual inspection of a wetland site. Factors represented in the AAI, include: (i) surrounding land use intensity; (ii) soil disturbance; (iii) hydrological alteration; (iv) habitat alteration within wetland; (v) vegetation community quality. The vegetation samples were collected in summer 2016 and winter 2017. All assessed indices were regressed against AAI to evaluate their performances. All assessed indices FQAI, FQAWet and WET-Health showed that hillslope seep wetland were impacted by human activities. FQAIall and WET-Health showed the strongest response to AAI in winter, while FQAIdom and FAQWet showed a weak response to AAI in all seasons. Overall, the findings of this study suggest that FQAIall and WET-Health are potentially better tools for assessing the biological conditions of hillslope seep wetland in South Africa. A novel trait-based approach was developed using seven plant traits and 27 trait attributes. Based on the developed approach, plant species were grouped into three potentially vulnerable groups in relation to grazing pressure. It was then predicted that species belonging to the highly vulnerable group would be less dominant at the highly disturbed sites, as well as in the winter season when grazing pressure is at its highest. The result corresponds largely with the seasonal predictions; however this was not the case for sites. The approach developed in this study worked and it was useful for predicting the potential responses of plant species in hillslope seep wetlands to grazing pressure. The success of the approach seasonally could be attributed to the careful selection of the traits, reflecting the mechanistic relationship between the grazing mode of stress on vegetation and trait-mediated biotic response. However, this still need to be refined using accurate vegetation cover methods that might have had impact on the lack of correspondence within sites. The results of the present study revealed that communities largely perceive hillslope seep wetlands as important ecosystems for their livelihoods. They recognise that the importance stems from services provided by the wetlands, particularly for livestock grazing during the dry season. Although hillslope seep wetlands are viewed as important ecosystems for livelihoods, the communities also perceive these wetlands as highly eroded ecosystems. Community members indicate willingness to strengthen local natural resource governance systems, which could lead to better management of hillslope seep wetlands. A range of protective strategies for hillslope seep were suggested by community members, including fencing, active herding and rotational grazing. The study suggests that active involvement of local communities is critical to the successful management of natural resources. The study highlights the need to consider the role of local people as influential components within social-ecological systems in order to promote effective management and conservation interventions of hillslope seep wetlands. Overall, the study highlights the criticality of an integrative social-ecological system approach for holistic management of hillslope seep wetlands within the studied catchment.
- Full Text:
- Date Issued: 2019
A classification of large wetlands in Africa’s elevated drylands based on their formation, structure, and hydrological functioning using Earth Observation (EO) data and Geographic Information System (GIS)
- Authors: Lidzhegu, Zwidofhelangani
- Date: 2020
- Subjects: Wetlands -- Africa -- Classification , Wetlands -- Africa -- Research , Wetlands -- Africa -- Monitoring , Topographical surveying -- Africa , Hydrological surveys == Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/142668 , vital:38100
- Description: Due to wetland inaccessibility and limited wetland geomorphological studies, there is limited information on the geomorphological origin and hydrological functioning of different types of wetlands in Africa’s elevated drylands. As a result, there is limited information for the development of a comprehensive wetland classification system that classifies wetlands based on long-term geomorphic processes that determine their formation and shape, their structure and hydrological functioning. Therefore, the current study was designed to classify large wetlands in Africa’s elevated drylands based on processes that determine their formation, and shape their structure and hydrological functioning using remote sensing and Geographic Information System (GIS) techniques. Although wetlands perform a number of hydrological functions including groundwater recharge and water purification, the current study focuses mainly on their flood attenuation function. Detailed analysis of topographic information was undertaken using Shuttle Radar Topographic Mission (SRTM) elevations measured at the scale of 30 m x 30 m. LandsatLook and Google Earth images, tectonic as well as geological data were used as supplementary data for developing an understanding of the origin, structure and hydrological characteristics of wetlands. The Principal Component Analysis (PCA) of wetland environmental variables was used to identify and explain wetland heterogeneity. The results of the study showed that fluvial processes, tectonic history and the evolution of Africa’s landscape played a fundamental role in the formation and evolution of wetlands. This study demonstrates a wide range of processes that contribute to wetland formation, structure and functioning. At one extreme it is clear that tectonic processes may be primarily responsible for the creation of basins that host wetlands. At another extreme, wetlands may be structured primarily by fluvial processes. At a third extreme are wetlands that superficially appear to be structured by fluvial processes, but which have their structures modified by gradual rising of the base level at their distal ends, either through marginal uplift adjacent to rift valleys, or through aggradation of a floodplain that blocks a tributary valley. Overall, the classification of wetlands considered in this study can be summarised into four distinct groupings, with two of these divided further into two groupings each: (1) Tectonic basins with little or no indication of fluvial development (Bahi and Wembere wetlands), (2) Tectonic basins evolving towards a wetland with a structure increasingly shaped by fluvial characteristics (Usangu wetland), (3) Fluvially modified valleys with a local base level at the toe of the wetland such as a resistant lithology or a tectonic control that limits the rate of incision of easily weathered and eroded lithologies, leading to valley widening and longitudinal slope reduction, which are of two distinct types: (a) With a catchment on Kalahari Group sediment that is transported fluvially as bedload, and therefore with no prominent alluvial ridge or backwater depressions (Upper Zambezi and Barotse wetlands), (b) With a catchment that produces abundant fine sediment that is deposited as overbank sediments, leading to channel migration via meandering and to the construction of an elevated alluvial ridge (Lufira wetland), (4) Fluvially modified basins with evidence of gradual elevation of the base level at the toe of the wetland, which are of two types: (a) Tectonic marginal rift valley uplift such that they behave more as depression wetlands rather than as wetlands shaped by fluvial processes (Kafue and Luapula wetlands), (b) Tributary valley wetlands blocked by aggradation of the trunk valley (Lukanga wetland). In conclusion, although few geomorphological studies have been conducted on southern African wetlands because of their inaccessibility, Africa’s surface topography and its historical evolution, as well as aridity, provide an opportunity for illustrating the important role that the long-term tectonic, geological and geomorphological processes play in determining wetland origin, structure and dynamics. GIS methodology and Earth Observation (EO) data on the other hand, provide a practical means for acquiring information on inaccessible and hard to traverse wetland systems. A novel cut-and-fill approach for delineating wetlands from a Digital Elevation Model (DEM) was presented as another way in which GIS methodology and Earth Observation (EO) data can provide practical means for assessing inaccessible and hard to traverse wetland systems.
- Full Text:
- Date Issued: 2020
A combined modelling approach for simulating channel–wetland exchanges in large African river basins
- Authors: Makungu, Eunice J
- Date: 2020
- Subjects: Watersheds -- Africa , Watershed management -- Africa , Water resources development -- Africa -- International cooperation , Floodplain management -- Africa , Wetland ecology -- Simulation methods -- Africa , Wetland management -- Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/123288 , vital:35424
- Description: In Africa, many large and extensive wetlands are hydrologically connected to rivers, and their environmental integrity, as well as their influence on downstream flow regimes, depends on the prevailing channel–wetland exchange processes. These processes are inherently complex and vary spatially and temporally. Understanding channel–wetland exchanges is therefore, indispensable for the effective management of wetlands and the associated river basins. However, this information is limited in most of the river basins containing large wetlands in Africa. Furthermore, it is important to understand the links between upstream and downstream flow regimes and the wetland dynamics themselves, specifically where there are water resource developments that may affect these links (upstream developments), or be affected by them (downstream developments). Hydrological modelling of the entire basin using basin-scale models that include wetland components in their structures can be used to provide the information required to manage water resources in such basins. However, the level of detail of wetland processes included in many basin-scale models is typically very low and the lack of understanding of the wetland dynamics makes it difficult to quantify the relevant parameters. Detailed hydraulic models represent the channel-wetland exchanges in a much more explicit manner, but require relatively more data and time resources to establish than coarser scale hydrological models. The main objective of this study was, therefore, to investigate the use of a detailed hydraulic wetland model to provide a better understanding of channel–wetland exchanges and wetland dynamics, and to use the results to improve the parameterisation of a basin-scale model. The study focused on improving the water resource assessments modelling of three data-scarce African river basins that contain large wetlands: the floodplains of the Luangwa and Upper Zambezi River basins and the Usangu wetland in the Upper Great Ruaha River basin. The overall objective was achieved through a combined modelling approach that uses a detailed high-resolution LISFLOOD-FP hydraulic model to inform the structure and parameters of the GW Pitman monthly hydrological model. The results from the LISFLOOD-FP were used to improve the understanding of the channel–wetland exchange dynamics and to establish the wetland parameters required in the GW Pitman model. While some wetland parameters were directly quantified from the LISFLOOD-FP model results, others, which are highly empirical, were estimated by manually calibrating the GW Pitman wetland sub-model implemented in excel spreadsheets containing the LISFLOOD-FP model results. Finally, the GW Pitman model with the inclusion of the estimated wetland parameters was applied for each basin and the results compared to the available downstream observed flow data. The two models have been successfully applied in southern Africa, with the GW Pitman model being one of the most widely applied hydrological models in this region. To address the issue of data scarcity, during setup of these models, the study mainly relied on the global datasets which clearly adds to the overall uncertainty of the modelling approach. However, this is a typical situation for most of the data scarce regions of the continent. A number of challenges were, however, faced during the setup of the LISFLOOD-FP, mainly due to the limitations of the data inputs. Some of the LISFLOOD-FP data inputs include boundary conditions (upstream and downstream), channel cross-sections and wetland topography. In the absence of observed daily flows to quantify the wetland upstream boundary conditions, monthly flow volumes simulated using the GW Pitman monthly model (without including the wetland sub-model) were disaggregated into daily flows using a disaggregation sub-model. The simulated wetland inflows were evaluated using the observed flow data for downstream gauging stations that include the wetland effects. The results highlighted that it is important to understand the possible impacts of each wetland on the downstream flow regime during the evaluations of the model simulation results. Although the disaggregation approach cannot be validated due to a lack of observed data, it at least enables the simulated monthly flows to be used in the daily time step hydraulic model. One of the recommendations is that improvements are required in gauging station networks to provide more observed information for the main river and the larger tributary inflows into these large and important wetland systems. Even a limited amount of newly observed data would be helpful to reduce some of the uncertainties in the combined modelling approach. The SRTM 90 m DEM (used to represent wetland topography) was filtered to reduce local variations and noise effects (mainly vegetation bias), but there were some pixels that falsely affect the inundation results, and the recently released vegetation-corrected DEMs are suggested to improve the simulation results. Channel cross-section values derived from global datasets should be examined because some widths estimated from the Andreadis et al. (2013) dataset were found to be over-generalised and did not reflect widths measured using high-resolution Google Earth in many places. There is an indication that channel cross-sections digitised from Google Earth images can be successfully used in the model setup except in densely vegetated swamps where the values are difficult to estimate, and in such situations, field measured cross-section data are required. Small channels such as those found in the Usangu wetland could play major role in the exchange dynamics, but digitising them all was not straightforward and only key ones were included in the model setup. Clearly, this inevitably introduced uncertainties in the simulated results, and future studies should consider applying methods that simplify extractions of most of these channels from high-resolution images to improve the simulated results. The study demonstrated that the wetland and channel physical characteristics, as well as the seasonal flow magnitude, largely influence the channel–wetland exchanges and wetland dynamics. The inundation results indicated that the area–storage and storage–inflow relationships form hysteretic curves, but the shape of these curves vary with flood magnitude and wetland type. Anticlockwise hysteresis curves were observed in both relationships for the floodplains (Luangwa and Barotse), whereas there appears to be no dominant curve type for the Usangu wetlands. The lack of well-defined hysteretic relationships in the Usangu could be related to some of the difficulties (and resulting uncertainties) that were experienced in setting up the model for this wetland. The storage–inflow relationships in all wetlands have quite complex rising limbs due to multiple flow peaks during the main wet season. The largest inundation area and storage volume for the Barotse and Usangu wetlands occurred after the peak discharge of the wet season, a result that is clearly related to the degree of connectivity between the main channel and those areas of the wetlands that are furthest away from the channel. Hysteresis effects were found to increase with an increase in flood magnitudes and temporal variations in the wetland inflows. Overall, hysteresis behaviour is common in large wetlands and it is recommended that hysteresis curves should be reflected in basin-scale modelling of large river basins with substantial wetland areas. At a daily time scale, inflow–outflow relationships showed a significant peak reduction and a delayed time to peak of several weeks in the Barotse and Usangu wetlands, whereas the attenuation effects of the Luangwa floodplain are minimal. To a large extent, the LISFLOOD-FP results provided useful information to establish wetland parameters and assess the structure of Pitman wetland sub-model. The simple spreadsheet used to estimate wetland parameters did not account for the wetland water transfers from the upstream to the next section downstream (the condition that is included in the LISFLOOD-FP model) for the case when the wetlands were distributed across more than one sub-basin. It is recommended that a method that allows for the upstream wetland inflows and the channel inflows should be included in the spreadsheet. The same is true to the Pitman model structure, and a downstream transfer of water can be modelled through return flows to the channel. The structure of the wetland sub-model was modified to allow an option for the return flows to occur at any time during the simulation period to provide for types of wetlands (e.g. the Luangwa) where spills from the channel and drainage back to the channel occur simultaneously. The setup of the GW Pitman model with the inclusion of wetland parameters improved the simulation results. However, the results for the Usangu wetlands were not very satisfactory and the collection of additional field data related to exchange dynamics is recommended to achieve improvements. The impacts of the Luangwa floodplain on the flow regime of the Luangwa River are very small at the monthly time scale, whereas the Barotse floodplain system and the Usangu wetlands extensively regulate flows of the Zambezi River and the Great Ruaha River, respectively. The results highlighted the possibilities of regionalising some wetland parameters using an understanding of wetland physical characteristics and their water exchange dynamics. However, some parameters remain difficult to quantify in the absence of site-specific information about the water exchange dynamics. The overall conclusion is that the approach implemented in this study presents an important step towards the improvements of water resource assessments modelling for research and practical purposes in data-scarce river basins. This approach is not restricted to the two used models, as it can be applied using different model combinations to achieve similar study purpose.
- Full Text:
- Date Issued: 2020
Developing macroinvertebrate trait- and taxonomically-based approaches for biomonitoring wadeable riverine systems in the Niger delta, Nigeria
- Authors: Edegbene, Ovie Augustine
- Date: 2020
- Subjects: Water – Pollution -- Nigeria -- Niger River Delta , Stream health -- Nigeria -- Niger River Delta , Water -- Pollution -- Measurement , Environmental monitoring -- Nigeria -- Niger River Delta , Water quality -- Nigeria -- Niger River Delta , Water quality biological assessment -- Nigeria -- Niger River Delta , Aquatic invertebrates -- Nigeria -- Niger River Delta , Stream restoration -- Nigeria -- Niger River Delta , Urban agriculture -- Nigeria -- Niger River Delta , Stream ecology -- Nigeria -- Niger River Delta
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/140660 , vital:37907
- Description: Riverine systems are increasingly subjected to pollution due to rapid urbanisation, industrialisation, and agricultural activities. Increasing pollution in freshwater systems impairs water quality, causes biodiversity loss and impairs aquatic ecosystem functionality and supply of ecosystem services. Rivers in the Niger Delta region of Nigeria are particularly vulnerable to urban pollution and agricultural activities as natural forests are increasingly replaced by urbanisation and agriculture. The differential effects of these pressures on the ecological processes of these river systems are poorly explored, as is the development of appropriate biomonitoring tools for routine monitoring of river health. In this study, a physico-chemically-based approach and macroinvertebrate trait- and taxonomic- approaches were developed to better understand the effects of multiple pressures on riverine systems, while developing multimetric indices to enable sustainable management of rivers within the region. Sixty-six stations in 20 river systems within the Edo and Delta States of the Niger Delta ecoregion were monitored seasonally for a period of five (2008–2012) years. The physico-chemically based approach makes apparent the extent of degradation of rivers and streams in the Niger Delta. For each dominant land use type, river stations were classified into least impacted stations (LIS), moderately impacted stations (MIS) or heavily impacted stations (HIS). Of 11 stations within urban catchments, only two were considered least impacted, suggesting that urgent measures are necessary to revise the current trajectories of urban rivers within the region. Most of the stations designated as MIS and HIS in the urban and urban-agriculture catchments were found to be significantly correlated with increased nutrients, EC and BOD5. Characteristics of most of the MIS and HIS within rivers in urban catchments evidenced the so-called urban stream syndrome, a state of persistent degradation of urban streams. The results of the traits and ecological preferences approach showed traits sensitive to urban and urban-agriculture pollution. Traits and ecological preferences that were associated with the LIS include the possession of hardshell, moderate and high sensitivities to oxygen depletion, very large body sized individuals (>20-40mm), swimmers, flattened body shape, a preference for temporary attachment, crawling, respiration with aerial/vegetation, possession of breathing tubes, possession of strap or other apparatus for respiration, streamlined body, and a high sensitivity to oxygen depletion. Permanent attachment as an ecological preference associated with LIS was also positively correlated with increasing dissolved oxygen (DO) and was deemed a pollution sensitive ecological preference. The possession of very small body size (<5mm), associated with HIS, was deemed a pollution-tolerant trait and was negatively correlated with DO, confirming the deteriorating state of the urban and urban-agricultural rivers. The impact of urban-forestry pollution on the distribution pattern of macroinvertebrate traits and ecological preferences was also explored in the selected rivers. Traits and ecological preferences such as possession of hard-shell, large body size, and grazing as a feeding preference which were significantly positively associated with the LIS, were also either significantly positively correlated with DO, or significantly negatively correlated with increasing any two of flow velocity, water temperature, BOD5 and nutrient. These traits and ecological preferences were deemed sensitive in forested rivers receiving urban pollution. Further, burrowing, the pupa aquatic stage, and predation which were significantly positively associated with HIS on the RLQ ordination, were also significantly negatively associated with DO. These traits were deemed tolerant of forested systems receiving urban pollution. Multimetric indices (MMI) were developed, validated and applied for urban, urban-agriculture and urban-forested (MMI-urban, MMI-urban-agric and urban-forest) areas. Of the 26 metrics that satisfactorily discriminated between the LIS, the MIS, and the HIS for MMI-urban, only five metric were retained for integration into MMI-urban, they are log VeL, Hemiptera abundance, % Coleoptera + Hemiptera, % Chironomidae + Oligochaeta and Evenness index. Further, of the 18 metrics that satisfactorily discriminated between the LIS, the MIS, and the HIS for MMI-urban-agric, only 12 metrics were retained and nine proved to be redundant. The nine metrics represent different measures; two of them were retained in addition to Chironomidae/Diptera abundance, % Odonata and Oligochaeta richness. The two metrics selected in addition to the hironomidae/Diptera abundance, % Odonata and Oligochaeta richness were the Margalef index and the logarithm of relative abundance of sprawler. For the MMI-urban-forest, 14 metrics satisfactorily discriminated between the LIS, the MIS, and the HIS, and 12 metrics were retained and 11 proved to be redundant. The non-redundant metric was Trichoptera abundance. Three metrics were further selected in addition to the Trichoptera abundance which include % Chironomidae + Oligochaeta, Coleoptera + Hemiptera richness and Shannon diversity. The MMI-urban and MMI-urban-agric indices performed better for LIS designated stations compared to the MIS and HIS deignated stations. The developed indices proved effective as biomonitoring tools for assessing the ecological health of rivers in the urban and urban-agriculture catchments within the Niger Delta. Overall, the results of the macroinvertebrate traits and ecological preferences, and taxonomic approaches showed the strength in the complementarity of both approaches in developing biomonitoring tools for assessing levels of deterioration in riverine systems. The study contributes significantly to understanding the ecology of riverine systems in the Niger Delta, particularly those subject to urban stresses, agricultural activities and urban pollution in forested systems, and thus makes an important contribution to the science and practice of biomonitoring in Nigeria where such studies are sparse.
- Full Text:
- Date Issued: 2020
Exploring and modelling the effects of agricultural land management and climate change on agroecosystem services in the Eastern Cape, South Africa
- Authors: Choruma, Dennis Junior
- Date: 2020
- Subjects: Agricultural ecology -- South Africa -- Eastern Cape , Agriculture -- Environmental aspects -- South Africa -- Eastern Cape , Crops and climate -- South Africa -- Eastern Cape , Corn -- Climatic factors -- South Africa -- Eastern Cape , Land use -- South Africa -- Eastern Cape
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/146756 , vital:38554
- Description: The aims of this study were to evaluate the impacts of agricultural land management strategies and climate change on irrigated maize production in the Eastern Cape, South Africa. To achieve these aims, the study was guided by two overarching research questions, subsequently broken down into more specific questions. The first research question examined the reasons behind farmers’ current agricultural land management practices, the values they assigned to different agroecosystem services, their perceptions of climate change and the adaptation strategies they used to address challenges associated with agricultural crop production and climate change. To answer these questions, a survey of conventional farmers in the Eastern Cape was carried out. The survey targeted farmers who used fertilisers and irrigation water in their day to day farming. Results showed that farmers recognised the different benefits that agroecosystems provided even though they were not familiar with the term ‘ecosystem services.’ Farmers assigned a high value to food provisioning compared to other agroecosystem services and managed their farms for maximum crop yields or maximum crop quality. Fertiliser and irrigation water management decisions were based on multiple factors such as cost, availability of farming equipment and crop yield or crop quality considerations. Survey results showed that while most farmers were able to state the amount of fertiliser used per growing season, the majority of farmers did not know the amount of water they used per growing season. From the farmers’ survey it was recommended that extension services and agricultural education programmes be strengthened in the region to increase farmers’ knowledge on effective agricultural land management strategies that support sustainable intensification. The second research question investigated the effects of agricultural land management strategies and climate change on crop yields in the Eastern Cape. This investigation was done in three steps. First, a crop model, the Environmental Policy Integrated Climate (EPIC) model was calibrated and validated using limited field data from maize variety trials carried out at the Cradock Research Farm in the Eastern Cape. Calibration and validation results proved satisfactory with model efficiencies (Nash Sutcliffe, NSE) greater than 0.5 for both calibration and validation. It was concluded that limited data from field trials on maize that only included grain yield and agricultural land management dates can be used for the calibration of the EPIC model to simulate maize production under South African conditions. In the second step, the calibrated model was applied to simulate different irrigation and fertiliser management strategies for maize production in the Eastern Cape. Different irrigation and Nitrogen (N) fertiliser levels were compared to find optimal irrigation and N fertiliser management strategies that would increase maize yields while minimising environmental pollution (nitrate leaching). Model outputs were also compared to the average yields obtained in the field trials (baseline) and to maize yields reported by farmers in the farmers’ survey. Results showed that improved management of irrigation water and N fertiliser could improve farmers’ maize yields from approximately 7.2 t ha-1 to approximately 12.2 t ha-1, an increase of approximately 69%. Results also revealed a trade-off between food provision and nitrate leaching. Simulations showed that increasing N fertiliser application under sufficient irrigation water levels would increase maize yields, however, this would be accompanied by an increase in N leaching. Lastly, the EPIC model was then applied to simulate the effects of future climate change on irrigated maize production in the Eastern Cape. For these simulations, the model was driven by statistically downscaled climate data derived from three General Circulation Models (GCMs) for two future climate periods, (2040-2069) and (2070-2099), under two Representative Concentration Pathways (RCPs): RCP 4.5 and RCP 8.5. Future maize yields were compared to the baseline (1980-2010) maize yield average. All three climate models predicted a decline in maize yields, with yields declining by as much as 23.8% in RCP 8.5, 2070-2099. Simulations also predicted increases in average daily maximum and minimum temperatures for both the two future climate periods under both RCPs. Results also indicated a decrease in seasonal irrigation water requirements. Nitrate leaching was projected to significantly increase towards the end of the century, increasing by as much as 373.8% in RCP 8.5 2070-2099. Concerning farmers’ perceptions of climate change, results showed that farmers were aware of climate change and identified temperature and rainfall changes as the most important changes in climate that they had observed. To adapt to climate change, farmers used a variety of adaptation strategies such as crop rotations and intercropping. Apart from challenges posed by climate change, farmers also faced other challenges such as access to markets and access to financial credit lines, challenges that prevented them from effectively adapting to climate change. The study therefore recommended that appropriate and adequate strategies be designed to help farmers in the region offset the projected decrease in maize production and increase crop yields while minimising negative environmental impacts.
- Full Text:
- Date Issued: 2020
Constraining simulation uncertainties in a hydrological model of the Congo River Basin including a combined modelling approach for channel-wetland exchanges
- Authors: Kabuya, Pierre Mulamba
- Date: 2021-04
- Subjects: Congo River Watershed , Watersheds -- Congo (Democratic Republic) , Hydrologic models , Rain and rainfall -- Mathematical models , Runoff -- Mathematical models , Wetland hydrology
- Language: English
- Type: thesis , text , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/177997 , vital:42897 , 10.21504/10962/177997
- Description: Compared to other large river basins of the world, such as the Amazon, the Congo River Basin appears to be the most ungauged and less studied. This is partly because the basin lacks sufficient observational hydro-climatic monitoring stations and appropriate information on physiographic basin properties at a spatial scale deemed for hydrological applications, making it difficult to estimate water resources at the scale of sub-basins (Chapter 3). In the same time, the basin is facing the challenges related to rapid population growth, uncontrolled urbanisation as well as climate change. Adequate quantification of hydrological processes across different spatial and temporal scales in the basin, and the drivers of change, is essential for prediction and strategic planning to ensure sustainable management of water resources in the Congo River Basin. Hydrological models are particularly important to generate the required information. However, the shortness of the available streamflow records, lack of spatial representativeness of the available streamflow gauging stations and the lack of understanding of the processes in channel-wetland exchanges, are the main challenges that constrain the use of traditional approaches to models development. They also contribute to increased uncertainty in the estimation of water resources across the basin (Chapter 1 and 2). Given this ungauged nature of the Congo River Basin, it is important to resort to hydrological modelling approaches that can reasonably quantify and model the uncertainty associated with water resources estimation (Chapter 4) to make hydrological predictions reliable. This study explores appropriate methods for hydrological predictions and water resources assessment in ungauged catchments of the Congo River Basin. In this context, the core modelling framework combines the quantification of uncertainty in constraint indices, hydrological modelling and hydrodynamic modelling. The latter accounts for channel-wetland exchanges in sub-basins where wetlands exert considerable influence on downstream flow regimes at the monthly time scale. The constraint indices are the characteristics of a sub-basin’s long-term hydrological behaviour and may reflect the dynamics of the different components of the catchment water balance such as climate, water storage and different runoff processes. Currently, six constraint indices namely the mean monthly runoff volume (MMQ in m3 *106), mean monthly groundwater recharge depth (MMR in mm), the 10th, 50th and 90th percentiles of the flow duration curve expressed as a fraction of MMQ (Q10/MMQ, Q50/MMQ, Q90/MMQ) and the percentage of time that zero flows are expected (%Zero), are used in the modelling approach. These were judged to be the minimum number of key indices that can discriminate between different hydrological responses. The constraint indices in the framework help to determine an uncertainty range within which behavioural model parameters of the expected hydrological response can be identified. Predictive equations of the constraint indices across all climate and physiographic regions of the Congo Basin were based only on the aridity index because it was the most influential sub-basin attribute (Chapter 5) for which quantitative information was available. The degree of uncertainty in the constraint Q10/MMQ and Q50/MMQ indices is less than 41%, while it is somewhat higher for the mean monthly runoff (MMQ) and Q90/MMQ constraint indices. The established uncertainty ranges of the constraint indices were tested in some selected sub-basins of the Congo Basin, including the Lualaba (93 sub-basins), Sangha (24 sub-basins), Oubangui (19 sub-basins), Batéké plateaux (4 sub-basins), Kasai (4 sub-basins) and Inkisi (3 sub-basins). The results proved useful through the application of a 2-stage uncertainty approach of the PITMAN model. However, it comes out of this study that the application of the original constraint indices ranges (Chapter 5) generated satisfactory simulation results in some areas, while in others both small and large adjustments were required to fully capture some aspects of the observed hydrological responses (Chapter 6). Part of the reason is attributed to the availability and quality of streamflow data used to develop the constraint indices ranges (Chapter 5). The main issue identified in the modelling process was whether the changes made to the original constraints at headwater-gauged sub-basins can be applied to ungauged upstream sub-basins to match the observed flow at downstream gauging stations. Ideally, only gauged sub-basin’s constraints can be easily revised based on the observed flow. However, the refinement made to gauged sub-basins alone may fail to substantially affect the results if ungauged upstream sub-basins exert a major impact on defining downstream hydrological response. The majority of gauging stations used in this analysis are located downstream of many upstream ungauged sub-basins and therefore adjustments were required in ungauged sub-basins. These adjustments consist of shifting the full range of a constraint index either towards higher or lower values, depending on the degree to which the simulated uncertainty bounds depart from the observed flow. While this modelling approach seems effective in capturing many aspects of the hydrological responses with a reduced level of uncertainty compared to a previous study, it is recommended that the approach be extended to the remaining parts of the Congo Basin and assessed under current and future development conditions including environmental changes. A 2D hydrodynamic river-wetland model (LISFLOOD-FP) has been used to explicitly represent the inundation process exchanges between river channels and wetland systems. The hydrodynamic modelling outputs are used to calibrate the PITMAN wetland sub-model parameters. The five hydrodynamic models constructed for Ankoro, Kamalondo, Kundelungu, Mweru and Tshiangalele wetland systems have been partially validated using independent estimates of inundation extents available from Landsat imagery. Other sources of data such as remote sensing of water level altimetry, SAR images and wetland storage estimates may be used to improve the validation results. However, the important objective in this study was to make sure that flow volume exchanges between river channels and their adjacent floodplains were being simulated realistically. The wetland sub-model parameters are calibrated in a spreadsheet version of the PITMAN wetland routine to achieve visual correspondence between the LISFLOOD-FP and PITMAN wetland sub-model outputs (Storage volumes and channel outputs). The hysteretic patterns of the river-wetland processes were quantified using hysteresis indices and were associated with the spill and return flow parameters of the wetland sub-model and eventually with the wetland morphometric characteristics. One example is the scale parameter of the return flow function (AA), which shows a good relationship with the average surface slope of the wetland when the coefficient parameter (BB) of the same function is kept constant to a value of 1.25. The same parameter (AA) is a good indicator of the wetland emptying mechanism. A small AA indicates a wetland that slowly releases its flow, resulting in a highly delayed and attenuated hydrological response in downstream sub-basins. This understanding has a practical advantage for the estimation of the PITMAN wetland parameters in the many areas where it is not possible, or where the resources are not available, to run complex hydrodynamic models (Chapter 7). The inclusion of these LISFLOOD-FP informed wetland parameters in the basin-scale hydrological modelling results in acceptable simulations for the lower Lualaba drainage system. The small wetlands, like Ankoro and Tshiangalele, have a negligible impact on downstream flow regimes, whereas large wetlands, such as Kamalondo and Mweru, have very large impacts. In general, the testing of the original constraint indices in the region of wetlands and further downstream of the Lualaba drainage system has shown acceptable results. However, there remains an unresolved uncertainty issue related to the under and over-estimation of some aspects of the hydrological response at both Mulongo and Ankoro, two gauging stations in the immediate downstream of the Kamalondo wetland system. It is difficult to attribute this uncertainty to Kamalondo wetland parameters alone because many of the incremental sub-basins contributing to wetland inflows are ungauged. The issue at Mulongo is the under simulation of low flow, while the high flows at the Ankoro gauging station are over-simulated. However, the pattern of the calibrated constraint indices in this region (Chapter 8) shows that the under simulation of low flow at Mulongo cannot be attributed to incremental sub-basins (between Bukama, Kapolowe and Mulongo gauging stations), because their Q90/MMQ constraint indices are even slightly above the original constraint ranges, but maintain a spatial consistency with sub-basins of other regions. Similarly, sub-basins located between Mulongo, Luvua and Ankoro gauging stations have high flow indices slightly below the original constraint ranges and therefore they are unlikely to be responsible for the over simulation of high flow at the Ankoro gauging station. These facts highlight the need for a further understanding of the complex wetland system of Kamalondo. Short-term data collection and monitoring programme are required. Important tributaries that drain to this wetland need to be monitored by installing water level loggers and periodically collecting flow data and river bathymetry. This programme should lead to the development of rating curves of wetland input tributaries. This would partially solve the unresolved uncertainty issues at the Ankoro and Mulongo gauging stations. The integrated modelling approach offers many opportunities in the Congo Basin. The quantified and modelled uncertainty helps to identify regions with high uncertainty and allows for the identification of various data collection and management strategies that can potentially contribute to the uncertainty reduction. The quantified channel-wetland exchanges contribute to the improvement of the overall knowledge of water resources estimation within the regions where the effects of wetlands are evident even at the monthly time scale. In contrast, ignoring uncertainty in the estimates of water resources availability means that water resources planning and management decisions in the Congo Basin will continue to be based on inadequate information and unquantified uncertainty, thus increasing the risk associated with water resources decision making. , Thesis (PhD) -- Faculty of Science, Institute for Water Research, 2021
- Full Text:
- Date Issued: 2021-04
The further development, application and evaluation of a sediment yield model (WQSED) for catchment management in African catchments
- Authors: Gwapedza, David
- Date: 2021-04
- Subjects: Sedimentation and deposition -- South Africa , Sedimentation and deposition -- Zimbabwe , Watersheds -- South Africa , Watersheds -- Zimbabwe , Watershed management -- Africa , Water quality -- South Africa , Water quality -- Zimbabwe , Modified Universal Soil Loss Equation (MUSLE) , Water Quality and Sediment Model (WQSED) , Soil and Water Assessment Tool (SWAT)
- Language: English
- Type: thesis , text , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/178376 , vital:42934 , 10.21504/10962/178376
- Description: Erosion and sediment transport are natural catchment processes that play an essential role in ecosystem functioning by providing habitat for aquatic organisms and contributing to the health of wetlands. However, excessive erosion and sedimentation, mostly driven by anthropogenic activity, lead to ecosystem degradation, loss of agricultural land, water quality problems, reduced reservoir storage capacity and damage to physical infrastructure. It is reported that up to 25% of dams in South Africa have lost approximately 30% of their initial storage capacity to sedimentation. Therefore, excessive sedimentation transcends from an ecological problem to a health, livelihood and water security issue. Erosion and sedimentation occur at variable temporal and spatial scales; therefore, monitoring of these processes can be difficult and expensive. Regardless of all these prohibiting factors, information on erosion and sediment remains an urgent requirement for the sustainable management of catchments. Models have evolved as tools to replicate and simulate complex natural processes to understand and manage these systems. Several models have been developed globally to simulate erosion and sediment transport. However, these models are not always applicable in Africa because 1) the conditions under which they were developed are not as relevant for African catchments 2) they have high data requirements and cannot be applied with ease in our data-scarce African catchments 3) they are sometimes complicated, and there are little training available or potential users simply have no time to dedicate towards learning these models. To respond to the problems of erosion, sedimentation, water quality and unavailability of applicable models, the current research further develops, applies and evaluates an erosion and sediment transport model, the Water Quality and Sediment Model (WQSED), for integration within the existing water resources framework in South Africa and application for practical catchment management. The WQSED was developed to simulate daily suspended sediment loads that are vital for water quality and quantity assessments. The WQSED was developed based on the Modified Universal Soil Loss Equation (MUSLE), and the Pitman model is a primary hydrological model providing forcing data, although flow data from independent sources may be used to drive the WQSED model. The MUSLE was developed in the United States of America, and this research attempts to improve the applicability of the MUSLE by identifying key issues that may impede its performance. Assessments conducted within the current research can be divided into scale assessment and application and evaluation assessment. The scale assessment involved evaluating spatial and temporal scale issues associated with the MUSLE. Spatial scale assessments were conducted using analytical and mathematical assessments on a hypothetical catchment. Temporal scale issues were assessed in terms of the vegetation cover (C) factor within the Tsitsa River catchment in South Africa. Model application and evaluation involved applying and calibrating the model to simulate daily time-series sediment yield. The model was applied to calibrated and validated (split-sample validation) in two catchments in South Africa, two catchments in Zimbabwe and three catchments were selected from the USA and associated territories for further testing as continuous daily time-series observed sediment data could not be readily accessed for catchments in the Southern African region. The catchments where the model was calibrated and validated range in size from 50 km2 to 20 000 km2. Additionally, the model was applied to thirteen ‘ungauged’ catchments selected from across South Africa, where only long-term reservoir sedimentation rates were available to compare with long term model simulations converted to sediment yield rates. The additional thirteen catchments were selected from areas of different climatic, vegetation and soils conditions characterising South Africa and range in size from 30 km2 to 2 500 km2. The current research results are split into a) MUSLE scale dependency and b) WQSED testing and evaluation. Scale dependency testing showed that the MUSLE could be spatially scale-dependent, particularly when a lumped approach is used, resulting in simulations of up to 30% more sediment. Spatial scale dependence in the MUSLE was found to be related to the runoff and topographic factors used and how they are calculated. The current study resorted to adopting a reference grid in applying the MUSLE, followed by scaling up the outputs to the total catchment area. Using a reference grid resulted in a general avoidance of the problem of spatial scale. The adoption of a seasonal vegetation cover factor was shown to significantly account for temporal changes of vegetation cover within a year and reduce over-estimations in sediment output. The temporal scale evaluation demonstrated the uncertainties associated with using a fixed vegetation cover factor in a catchment with variable rainfall and runoff pattern. The WQSED model evaluation showed that the model could be calibrated and validated to provide consistent results. Satisfactory model evaluation statistics were obtained for most catchments to which the model was applied, based on general model evaluation guidelines (Nash Sutcliffe Efficiency and R2 > 0.5). The model also performed generally well compared to established models that had been previously applied in some of the study catchments. The highest sediment yields recorded per country were 153 t km-2 year-1 (Tsitsa River; South Africa), 90 t km-2 year-1 (Odzi River; Zimbabwe) and 340 t km-2 year-1 (Rio Tanama; Puerto Rico). The results also displayed consistent underestimations of peak sediment yield events, partly attributed to sediment emanating from gullies that are not explicitly accounted for in the WQSED model structure. Furthermore, the calibration process revealed that the WQSED storage model is generally challenging to calibrate. An alternative simpler version of the storage model was easier to calibrate, but the model may still be challenging to apply to catchments where calibration data are not available. The additional evaluation of the WQSED simulated sediment yield rates against observed reservoir sediment rates showed a broad range of differences between the simulated and observed sediment yield rates. Differences between WQSED simulated sediment and observed reservoir sediment ranges from a low of 30% to a high of > 40 times. The large differences were partly attributed to WQSED being limited to simulating suspended sediment from sheet and rill processes, whereas reservoir sediment is generated from more sources that include bedload, channel and gully processes. Nevertheless, the model simulations replicated some of the regional sediment yield patterns and are assumed to represent sheet and rill contributions to reservoir sediment in selected catchments. The outcome of this study is an improved WQSED model that has successfully undergone preliminary testing and evaluation. Therefore, the model is sufficiently complete to be used by independent researchers and water resources managers to simulate erosion and sediment transport. However, the model is best applicable to areas where some observed data or regional information are available to calibrate the storage components and constrain model outputs. The report on potential MUSLE scale dependencies is relevant globally to all studies applying the MUSLE model and, therefore, can improve MUSLE application in future studies. The WQSED model offers a relatively simple, effective and applicable tool that is set to provide information to enhance catchment, land and water resources management in catchments of Africa. , Thesis (PhD) -- Faculty of Science, Institute for Water Research, 2021
- Full Text:
- Date Issued: 2021-04
Ecological infrastructure importance for drought mitigation in rural South African catchments: the Cacadu Catchment case example
- Authors: Xoxo, Beauten Sinetemba
- Date: 2021-10
- Subjects: Sustainable Development Goals , Water security South Africa , Remote sensing , Watershed restoration South Africa , Restoration ecology South Africa , Ecosystem services South Africa , SDG 15.3.1
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/191203 , vital:45070
- Description: Water scarcity is recognised as one of the significant challenges facing many countries, including South Africa. The threat of water scarcity is exacerbated by the coupled impacts of climate and anthropogenic drivers. Ongoing droughts and continued land cover change and degradation influence the ability of catchments to partition rainwater runoff, thereby affecting streamflow returns. However, quantifying land degradation accurately remains a challenge. This thesis used the theoretical lens of investing in ecological infrastructure to improve the drought mitigation function in rural catchments. This theoretical framework allows for a social-ecological systems approach to understand and facilitate science-based strategies for promoting ecosystem recovery. Specifically, this study aimed to explore the role and benefit of ecological infrastructure for improving drought mitigation, and consequently, water security for rural communities. Thus, this study sought to assess the consequences of human actions to catchment health status using the 15th Sustainable Development Goal indicator for the proportion of degraded land over the total land area as a surrogate. Secondly, hydrological modelling was used to describe how different land covers influence catchment hydrology, which related to how ecological infrastructure enables drought risk-reduction for mitigation regulation. Finally, this study developed a spatial prioritisation plan for restoration to improve drought mitigation for four focal ecological infrastructure (EI) categories (i.e. wetlands, riparian margins, abandoned agricultural fields and grasslands). The focal EI categories were selected for their importance in delivering water-related ecosystem services when sustainably managed. Chapter 1 sets the scene (i.e. provides the study background) and Chapter 2 provides a review of the literature. In Chapter 3, the recently released global GIS toolbox (TRENDS.EARTH) was used for tracking land change and for assessing the SDG 15.3.1 degradation indicator of i.e. Cacadu catchment over 15 years at a 300 m resolution. The results showed a declining trend in biomass productivity within the Cacadu catchment led to moderate degradation, with 16.79% of the total landscape degraded, which was determined by the pugin using the one-out, all-out rule. The incidence of degradation was detected in middle reaches of the catchment (i.e. S10F-J), while some improvement was detected in upper reaches (S10A-C) and lower reaches (S10J). In Chapter 4, a GIS-based Analytic Hierarchical Process (AHP) based on community stakeholder priorities, open-access spatial datasets and expert opinions, was used to identify EI focal areas that are best suitable for restoration to increase the drought mitigation capacity of the Cacadu catchment. The collected datasets provided three broad criteria (ecosystem health, water provision and social benefit) for establishing the AHP model using 12 spatial attributes. Prioritisation results show that up to 89% of the Cacadu catchment is suitable for restoration to improve drought mitigation. Catchments S10B-D, and S10F, S10G and S10J were highly prioritised while S10A, S10E and S10H received low priority, due to improving environmental conditions and low hydrological potential. Areas that were prioritised with consideration for local livelihoods overlap the areas for drought mitigation and form a network of villages from the middle to lower catchment reaches. Prioritised restoration areas with a consideration of societal benefit made up 0.56% of wetlands, 4.27% of riparian margins, 92.06% of abandoned croplands, and 51.86% of grasslands. Chapter 5 reports on use of the Pitman groundwater model to help understand the influence of land modification on catchment hydrology, and highlight the role of restoration interventions. The Cacadu catchment is ungauged, therefore the neighbouring Indwe catchment was used for parameter transfer through a spatial regionalisation technique. Results suggest that degradation increases surface runoff and aggravates recharge reduction, thereby reducing streamflow during low flow periods. In areas where there is natural land cover recovery, the Pitman Model simulated similar dry season streamflow to the natural land cover. Combining the outcomes from the three assessments allowed the study to highlight the role and benefits of ecological infrastructure in terms of drought mitigation. Study findings were interpreted to make recommendations for the role and benefit of ecological infrastructure for drought mitigation at a landscape scale and tertiary catchment level, within the context of available management options. The results support the notion that multiple science data sources can promote investments in ecological infrastructure. However, better spatial and temporal resolution datasets at a national level are still needed to improve the accuracy of studies such as the one outlined in this thesis. The study recommends adopting better ecosystem protection approaches and collaborative governance at multiple levels to reduce the vulnerability of rural communities to drought impacts. , Thesis (MSc) -- Faculty of Science, Institute for Water Research, 2021
- Full Text:
- Date Issued: 2021-10