Doctoral Degrees (Institute for Groundwater Studies (IGS))
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Browsing Doctoral Degrees (Institute for Groundwater Studies (IGS)) by Advisor "Vermeulen, P. D."
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Item Open Access Environmental geochemistry of the Waterberg coalfields(University of the Free State, 2015-07) Deysel, Lore-Marie; Vermeulen, P. D.English: The Waterberg Coalfields represent the last area in South Africa which contain large quantities of coal resources. The most important issue with economic growth and development is to take measures to minimise the impact on the environment. With the ever increasing demand for energy, the demand for continuous mining of coal increases and thus expands into areas not previously mined. The by-products of coal mining and the production of electricity from the coal leaves an environmental footprint. For this footprint to be minimised, all the risks associated with mining should be available and understood. Since there are still large coal deposits in the Waterberg which can be mined by opencast mining, the risk of the geological units still to be mined was assessed. Acid generation due the oxidation of mainly pyrite is a source of contamination that can impact the groundwater and to a lesser or no extend the surface water from the mining facilities. Another environmental risk is air pollution from mines, includingthat of Medupi Power Station which will commence shortly. It is a very dry area and thus the aquifers must be protected as far as possible. In this study area,coal is mined by the opencast method from the Karoo formation There currently only one active coal mine in the study area, namely the Grootegeluk mine which started operation in 1980. Samples were collected from exploration boreholes in all three areas in the region (partly weathered, Full succession and Middle Ecca). Acid-Base Accounting was done on all 800+ samples and it indicated that the interburden and discards contained the highest AMD potential while the overburden had the highest buffering capacity. The impact is clear on some of the monitoring boreholes on the site. Unlined facilities lead to the contamination of the aquifers to a point where the pH of the water is acidic. The monitoring boreholes close to the ash dump is affected by a raise in the total dissolved solids due to calcium and sulphate leaching from the ash. To get the total impact or toxicity potential of samples, it is necessary to identify the elements that are available in the different wastes that can leach into the environment. All the risks associated with the different geological units should be known so that the best decision and planning of waste facilities for future extensions can be made, and so that the negative footprint on the environment can be minimised.Item Open Access Estimation of episodic groundwater recharge in semi-arid fractured hard rock aquifers(University of the Free State, 2010-08) Van Wyk, Ettienne; Van Tonder, G. J.; Vermeulen, P. D.The semi-arid regions of southern Africa cover large portions of settled land where domestic and agricultural activities depends on isolated groundwater systems replenished by irregularly occurring rainfall events. Southern African rainfall patterns are regulated by the annual oscillation of winter-summer weather systems and most of all, abrupt changes in regional atmospheric patterns, which may result in either wet/dry cycles. Given the highly differential hydro-climatic conditions and hydrogeological environment in semi-arid regions, effective groundwater recharge events are episodic in nature and largely occur once in every five years. Sustainable, medium-term management of local groundwater resources requires dynamic hydrological information to ensure a healthy supply-demand balance; thus requiring dedicated hydrological monitoring. High-level monitoring programmes on a few experimental sites have produced localised hydrological data, which illustrate how erratic groundwater resources are replenished. For many years, it was postulated that groundwater resources were recharged every time the total annual rainfall peaks a certain threshold. This postulation may hold in humid regions, but surely not elsewhere in the drier parts of South Africa. Semi-arid regions portray a flattish regional landscape with occasionally elevated parent rock windows and mountainous regions. Soil cover is restricted to low-relief areas, and lacks the thick mature soils distinctive of the humid areas. Fractured hard rock windows with very little soil cover represent potential groundwater recharge terrains, allowing recharge-producing surplus rainfall to infiltrate directly into the underlying aquifer. The hydrogeological conditions of hard rock terrains in the same-arid environment do vary in terms of the rock types and their response on weathering processes. Nonetheless, an array of joints and fractures running from ground surface into the SZ represents fast and effective pathways when episodic high rainfall events occur. Mature soil/regolith profiles in plain areas enhances surface run-off and support local floods in rivulets where riparian vegetation and open-water evaporation intercepts most of the available bank storage and depression recharge. Atmospheric moisture is, in principal, generated by warm, evaporating maritime waters, and is therefore marked by its hydrochemical signature. This signature changed abruptly during its continental migration, and finally manifests as cloud water. Winter rainwater specifically demonstrates the impact of oceanic aerosols, hence characterized by a prominent NaCl composition. Summer rainwater is a diluted version due to continental rainfall/evapotranspiration events, and is transformed by anthropogenic airborne substances peaking during the late-winter months. The hydrogeochemical composition of rainwater is therefore quite diverse, and needs logic monitoring to understand its seasonal cyclic oscillation. Short-term hyetograph observations report episodic rainfall events, occurring mostly over the January-March period of wet hydrological cycles. These are spaced over a period of 4 to 8 days, of which at least one rain event exceeds ~45 mm, associated with a rain-rate intensity of >1.5 mm·h-1. Extraordinary depleted rainwater hydrochemistry and isotopic compositions are associated with these rain weeks, which are significantly different from normal seasonal concentrations. Wet Cl− concentrations during these high rainfall periods are almost an order of magnitude lower than the average annual values. Hyetograph-hydrograph sets confirm that extraordinary groundwater recharge occurs as the result of episodic rainfall events. Hydrogeochemical profiling in the upper section of the unsaturated zone verify the presence of different compositions which probably indicate different modes of recharged rainwater percolation in fractured, hard rock terrains. Hard rock profile sections below the rebound water table interface containing almost 50% less Cl− than country-wide background values of ~40 mg·H-1. Isotopic compositions in a typical rain week period report similar depleted concentrations and resemble a prominent amount effect. Such depleted rainwater is merely linked to specific seasons, for example the rainfalls of 2003-2004, 2005-2006 and 2007-2008 hydrological years can be clustered as high rainwater input periods with notable lighter isotopic compositions; around - 7.5‰ M18O, -41‰ M2H. The fact that most of the two (2) meter vertical profiles reported relatively negative isotopic compositions (-8‰ M18O, -44‰ M2H), indicates a high probability of preferential recharge with pristine rainwater with even more negative isotopic composition. Direct groundwater recharge estimations from local, short-term rainfall and groundwater rebound stage hydrochemical data proposes a recharge value <2% in most flat lying, semi-arid regions. Although fractured hard rock terrains are isolated, it allows in the order of 4%, where as local mountainous areas are high at 14%; obviously enhanced by orographic rainfall development. Recharge on dolomitic terrains are highly variable due to diverse ground surface conditions, and may vary between 6% in flat lying plains to 13% in mountainous regions (Kuruman Hills at Kuruman). Groundwater recharge varies significantly spatially. The control by prominent soil/regolith cappings is that high that establishing realistic recharge figures for a particular area, will require a dedicated soil mapping programme to identify direct recharge terrains.Item Open Access Quantifying the role of groundwater in sustaining Groenvlei, a shallow lake in the southern Cape region of South Africa(University of the Free State, 2015-11-19) Parsons, Roger Paul; Vermeulen, P. D.Eight of the 21 Ramsar-designated wetlands in South Africa are located in similar geohydrological settings as Groenvlei, a 359 ha lacustrine wetland found east of Sedgefield in the southern Cape. Groenvlei is unique as it is isolated from the sea and neither fed nor drained by rivers. Consequently, the lake is fed only by rainfall and groundwater inflow. Losses comprise evaporation and groundwater outflow. These characteristics result in a relatively uncomplicated hydrological system that allows for the geohydrological component to be quantified and understood. Using climatic and lake data monitored by the Department of Water Affairs and geohydrological data collected over a period of a decade, research was conducted to quantify the groundwater contribution to the system and develop an improved understanding of the hydrology of Groenvlei. A daily water balance based on rainfall, adjusted S pan evaporation data and lake levels was used to compute that the nett groundwater contribution to Groenvlei amounted to about 0.3 mm/d. It was shown that S pan evaporation data adjusted by coefficients prescribed by Midgley et al. (1994) should be used to quantify lake evaporation, and that the reed collar transpired 10% to 30% more during summer than evaporated from open water. No water is transpired by the reed collar in winter as the vegetation is dormant. Integrating the water balance results with steady-state Darcian flow calculations and a chemical mass balance indicated direct rainfall (71.6%) and groundwater inflow along the western and northern boundaries of the lake (28.4%) constituted inflow into the system. This is balanced by evaporation from open water (61.7%), transpiration from the reed collar in summer (21.4%) and groundwater outflow along the southern boundary (16.9%). This latter component invalidates claims that Groenvlei is endorheic in character. Recharge to the Eden Primary aquifer was estimated to be in the order of 20% MAP. It was calculated only 5.7% of rainfall in the lake catchment discharges into the lake. The balance of rain entering the subsurface is lost through terrestrial evaporation or discharges into the sea via the deeper part of the aquifer. It was interpreted that the deceptively thick vadose zone plays a buffering role in the hydrology of the area and that evapotranspiration losses are appreciable. The importance of the reed collar was further exemplified by the retention of salts in the vegetative fringe. Salts are assimilated by the vegetation and retained in the hyporheic zone until re-entrained into the main water body through wind and wave action. This results in only part of the salt load leaving the lake along the southern boundary and affecting groundwater quality between the lake and the sea. Further research is required to confirm this. The results of the research allowed for tools to be developed to assess the impact of groundwater abstraction from the lake’s catchment on lake levels and water quality. These tools could also be used to demonstrate Groenvlei has long since lost its connection to the marine or estuarine environments, with a new equilibrium being reached within 120 years of disconnect. The young lake is dynamic in character and rapidly responds to hydrological change. In its short history, Groenvlei has adapted and responded to changes in both sea level and climate, collectively resulting in the present-day system. In addition to highlighting the importance of sound conceptualisation, data quality and a convergence of evidence, the outcomes of this study challenged the findings of Roets’ (2008) PhD research and found no scientific evidence to support his contention that Groenvlei is sustained by underlying Table Mountain Group aquifers. It was also found that the permeability south of Groenvlei is not low and the extent of the lake catchment is 25 km2. Past research of Groenvlei has resulted in a number of misconceptions and it was argued a need exists to link hydrologists and ecologists to better understand wetlands, with each contributing specific skills and knowledge. An important contribution of the research documented in this thesis is that the approach used can be applied to similar wetlands where the role of groundwater might be less obvious because of river flows and tidal exchange. The importance of sound conceptualization and direct rainfall onto wetlands, quantification of evaporative losses using S pan data and coefficients prescribed by Midgley et al. (1994), and the relationship between open water losses and transpiration losses are three aspects that could improve the understanding and quantification of lake – groundwater interaction elsewhere. A limitation to understanding the geohydrology of Groenvlei is the lack of information pertaining to aquifer thickness. It is therefore recommended four boreholes be drilled to either bedrock or at least 100 m in depth (whichever is reached first) to quantify the thickness of the aquifer. Other limitations that require attention include: • Uneven spatial distribution of the geohydrological data; • Lack of information of losses from open water and the reed collar; and • Absence of monitored groundwater data needed to address temporal relationships between groundwater and the lake.