Conference Abstracts

All Abstracts were presented at the Groundwater Conferences

Displaying 101 - 150 of 575 results
Title Presenter Name Presenter Surname Area Conference year Keywords

Abstract

The Western Cape has experienced a drought since 2015 and one of the regions most adversely affected by this drought was the Swartland. Towns in this region make use of water supplied by the Vo?lvlei Dam, which is the Swartland Municipality's bulk and only source of water. Groundwater exploration was undertaken to find alternative sources of water which would be used to relieve some of the pressure on surface water resources. A total of seven towns and communities were identified as high risk and most vulnerable. These include Abbotsdale, Koringberg, Malmesbury, Moorreesburg, Riebeek Kasteel, Riebeek West and Riverlands. This project posed several challenges, namely: available land, proximity to infrastructure and unfavourable geology (in terms of groundwater potential). The project had mixed results in terms of quality and yield. This paper presents the approach and results of the groundwater development.

Abstract

Big data analytics (BDA) is a modern and innovative platform of applications that include advanced analytical techniques such as data mining, statistical analysis, artificial intelligence, machine learning, and natural language processing. Regional data are generated through groundwater monitoring, remote sensing applications or global circulation models (GCM), however this is often too course for a local understanding. Groundwater managers rely on locally relevant information for effective operational decision making, however this is often missing. A Transboundary Aquifer (TBA) Analytic Framework was developed to match, integrate and model local hydrogeological data with regional earth-observation data using BDA. Drawing on the literature on BDA, a reference architecture for the TBA analytical framework was identified for application to various groundwater management scenarios in the Ramotswa Dolomitic Aquifer (Botswana - South Africa) and Shire Valley Alluvial Aquifer (Malawi - Mozambique). The TBA analytical framework allows for local clouds to store the local and regional structured and unstructured datasets and interconnecting these local clouds through a federated cloud infrastructure. In this regard, tools that are incorporated in the TBA analytical framework include data ingestion operators, data transformation operators, and feature extractors. Various machine learning algorithms and statistical techniques are incorporated in the TBA analytical framework to downscale the regional datasets. The downscaling involves selection of potential predictors and predictants variables based on data needs to address local groundwater management scenarios such as regulating groundwater abstraction to prevent groundwater depletion. Using the downscaled data the TBA analytical framework can be utilised to uncover patterns and statistical relationships in the datasets in order to model local groundwater processes such as cone of depression, groundwater levels forecasting, well protection zoning, amongst others.

Abstract

Extensive geological, mineralogical and geochemical research have been done on the Insizwa layered mafic sill intrusion, located in the northern part of the Eastern Cape province, South Africa. This focus is understandable in the light of its potential for Cu, Ni and PGM extraction. However, the complex is also linked to a potentially significant groundwater reserve, and is located in a populated rural area with numerous communities residing on or in close proximity to the intrusion. These communities rely on local groundwater sources and recent groundwater development projects have suggested that groundwater yield potential is higher in its host Karoo sedimentary rocks adjacent to the intrusion than farther away. The proposed research will endeavour to investigate the structural geological features that influence groundwater yield, quality and community water supply potential in the Insizwa and surrounding area to provide a baseline for integrated quantified groundwater management, to meet community needs and awareness.

Abstract

Frequently hydrogeologists are required to site boreholes in areas that are not the optimal for groundwater supply and are given budgets that don't allow rigorous science. This paper presents case studies from Windhoek (Namibia), Matatiele (Eastern Cape Province) and the greater Port Elizabeth area where high success rates and yields were achieved by adopting a no-compromise approach to budgets and target areas. In Windhoek, the aim was to locate and intercept faults at depths up to ~500 m. Following geological mapping and geophysics, angled boreholes were drilled to establish fault dips prior to successfully drilling deep production boreholes. In the Matatiele area, an extensive area was flown with airborne geophysics prior to surface geophysical surveys. In Port Elizabeth the electricity supply to a large area was temporarily cut in order to get undisturbed geophysical data. In Jeffreys Bay, the main entrance road was virtually blocked to cater for geophysical surveys. Hankey town is located in a poor groundwater area, so drilling on private land about 20 km out of town had to be negotiated in order to target an aquifer suitable for the town's supply. These are some of the examples that will be presented in the paper. In most areas drilling yields in excess of 50 L/s were achieved, and the success can be attributed to not compromising on doing rigorous science in the right areas.

Abstract

Assessment of aquifer vulnerability to contamination is receiving renewed attention due to recent extreme events as demand for groundwater as alternative sources of water supply intensifies. In this study, GIS-based modeling of the impact of land-based activities and climate variability is employed to quantify the risk to quality deterioration of groundwater resource, delineate potential areas and highlight degree of vulnerability in the Cape Flats aquifer. The study used Scenariorcp85 CMIP5 AR5 climate change datasets downscaled from GCM using WaterWorld model. The WaterWorld is physically based global model for water balance includes all data required for application with a spatial resolution at 1-square km (Mulligan, 2009). The modeling results suggest that water balance for the predominantly low-lying flat central portion receives recharge ranges from 44 to 376 mm/yr. This reflects the area precipitation ranges from 500 to 800 mm/yr. Actual evapotranspiration (mm/yr) ranges from 92 to 1,200. The cmip5rcp85worldclimhe20412060 simulation main results indicate water balance (mm/yr) for the area predict to a minimum of -1,100 and maximum of 1,100. Actual evapotranspiration (mm/yr) ranges from 67 to 1,200. This led to an increase in evapotranspiration for the area of 13 mm/yr (2.5 %) that lead to an overall decrease in the water balance of -44 mm/yr (22 %). The human influence on water quality was simulated based on the human footprint index. The risk of contamination is largely attributed to the change in urban areas, pastures and cover of bare ground. In order to address the significant spatial variability of groundwater recharge and potential contamination risk occurring throughout the area, a GIS-based approach is used. The result underscores that GIS-based models are powerful tools to integrate spatiotemporal data and make assessment possible to improve understanding of water security in light of climate and land use change scenarios.

Abstract

In the recent drought of the Cape, Drakenstein Municipality sought to improve its water security and supply through including groundwater into the municipal water supply network. After a desktop assessment of the geology and hydrogeology of the municipal area, it was initially proposed that groundwater development target the Table Mountain Group Aquifer (TMGA), which lies along and within the eastern boundary of the municipal border and is expected to yield 2 - 5 L/s/borehole. The alternate aquifers of the area are in the bedrock shales of the Malmesbury Group and the crystalline granites of the Cape Granite Suite. These are both categorized to have expected yields of 0.1 - 0.5 L/s/borehole. It was then decided that despite the substantially higher estimate potential of targeting the TMGA further away from the towns, investigations would focus on exploration on municipal land closer to local infrastructure, to limit on the costs of the additional infrastructure that would be required to get the water to the towns. This resulted in the exploration being predominantly focused on inferred bedrock faulting in the Malmesbury Group within Paarl; and the contact of the Malmesbury Group to the Wellington Pluton granite in Wellington, as well as part of the Wellington- Piketberg Fault. While several boreholes drilled in exploration in both the Malmesbury Group and the Cape Granite Suite confirmed the generally low yield expectations (< 1 L/s), surprisingly high yielding boreholes were drilled in the town of Paarl. Initial exploration of the potential fault was done in 2017 with electromagnetic and resistivity profiling to look for subsurface changes that may be associated with fracture zones. After the results of these surveys seemed to show some change in geophysical properties in the subsurface where a fault was inferred, exploration drilling along some of these profiles was conducted. In particular, exploration drilling at the Boy Louw Sportsfield in Paarl intersected water strikes from 60 - 90 mbgl in excess of 20 L/s blow yields. After a 3-day yield test with a further day for recovery in early 2018, a production wellfield was planned. Production drilling involved drilling larger diameter boreholes that would allow for higher flow rate pump installations than the typical 127 mm (PVC sleeved) to 165 mm inner diameter boreholes found in the region. Drilling depths of 100 - 150 mbgl were reached, by which depths airlift yields were exceeding 20 L/s as expected from the initial exploration drilling. Wellfield testing of the boreholes was performed by conducting two separate simultaneous borehole pumping tests at 38 L/s and 44 L/s, during which all available boreholes in the wellfield were monitored for water level changes. Based on the data analyses of these tests, the sustainable yield of the wellfield was initially estimated to be up to 60 L/s. As there was still some uncertainty regarding the high yields in a geological environment which was typically much lower yielding, two operational recommendations were put in place. The first was that the boreholes be equipped with pumps capable of adjusting flow rates as well as water level monitoring infrastructure to allow for informed management of the resource. The water level monitoring was also to be installed in the exploration boreholes to monitor the drawdown outside of the production boreholes. The second was that a one-month step-wise start to production should occur. During this period the wellfield was to start with a week of continuous pumping at a lower rate than estimated as sustainable, with increasing rates each week. This was recommended in such a way as to bridge the gap between the cumulative wellfield test rates and the cumulative wellfield recommended rate of abstraction and allow for any final optimizations to be made to this rate.While the first recommendation of monitoring infrastructure and variable rate pump installations was adhered to, in May 2019 the wellfield was abstracted from at the full initial recommendation of 60L/s. After a week of abstraction, three of the production boreholes were performing as expected fromthe wellfield test results, while one of the production boreholes had begun to drawdown more rapidly than expected. It was noted that this began to occur at a lower depth than what was reached during the 2018 wellfield tests. The rate of the individual borehole was reduced and abstraction continued for another two weeks with the new wellfield total of 54 L/s. The drawdown data of the borehole in question during the May 2019 abstraction was then re-analysed within the context of the wellfield, and with the increased drawdown data, to produce final wellfield production recommendations. As with all sustainable yield testing of boreholes, the choice of available drawdown is critical to the success of the analysis. In the Boy Louw Wellfield, it is likely that had higher abstraction rates been used during the wellfield testing, greater drawdowns may have revealed the inflection point in one of the production boreholes. Accounting for this in the initial analyses would have resulted in a more accurate initial wellfield recommendation. Additionally, the recommendations of a step-wise start to production would have likely revealed the same thing. While one of the production boreholes is now recommended to be operated at less than 50% of its initial recommendation due to the more recent identification of an inflection point, the total abstraction rate is still 90% of the initial wellfield tests' analyses recommendation. Against all odds, this allows an abstraction rate of 54 L/s from 4 production boreholes within a geological setting previously characterized as 0.1 - 0.5 L/s/borehole. Based on these results, it is recommended that future wellfield developments can adopt a similar methodology of iteratively increasing the development of a wellfield through scientific principles and testing. Wellfield testing should aim to cause sufficient drawdown in the production boreholes, as well as identify and quantify the cumulative interactions between adjacent boreholes within the wellfield. Should this not be achieved, a step-wise start to production with the ability to optimize flow rates is strongly recommended.

Abstract

South Africa has committed to achieving the United Nations Sustainable Development Goals (SDG's) by 2030. But what does this mean and how does groundwater fit in to this? SDG 6 in particular focuses on ensuring universal access to safe and affordable drinking water for all by 2030. SDG 6 requires that the country protects and restores water-related ecosystems such as forests, mountains, wetlands, aquifers and rivers which are essential if we are to mitigate water scarcity. To accomplish this, South Africa has proceeded to align various plans, strategies, and policies to encompass the targets of the SDG's. This paper will focus on SDG sub-goal 6.3 which incorporates improvement of water quality and sub-goal 6.6 which involves protection and restoration of ecosystems. The methodology given by the UN for the groundwater in indicator 6.3.2 stipulates that countries are required to report on "proportion of water with good ambient water quality", in South Africa however we had to domesticate the indicator i.e. render it suitable for South African conditions so we changed the methodology to "proportion of water the conforms to the Water Quality Objectives (WQO's)" but there are virtually no WQO's developed for groundwater. Four core groundwater quality parameters (Electrical Conductivity, pH, Nitrate and Sulphate) are available through ZQM stations categorized through 65 hydrogeological (Vegter) regions. Groundwater water quality baseline is calculated as a reference period/range per hydrogeological region. For SDG 6.6, the indicator required for groundwater is "Quantity of groundwater within aquifers" The methodology received by the UN for "Quantity of groundwater within aquifers" required a baseline (average reference period of five years) in meters per hydrogeological region. This indicator is again domesticated for South Africa and based on the 40-60 percentiles of groundwater levels per hydrogeological region. There are a number of future indicators that can be included for aquifers under SDG 6.6, but the groundwater sector needs to come together and decide what is important to report on. These SDG targets reporting has given the Water and Sanitation sector a new look at data. It has forced us to critically think of concepts such as baseline and performance monitoring. We now know where our data gaps and targets are, and we have to provide an action plan to address these.

Abstract

The uncertainties associated with both the sampling process and laboratory analysis can contribute to the variability of the results. In most cases, it does appear that if the water samples have been analysed by an accredited laboratory, the results are acceptable. While the accreditation of analytical laboratory and therefore its credibility is very important to uphold quality and integrity, the same should be said about the sampling process. The quality and credibility of a sampling process is typically left to the responsibility of the appointed groundwater practitioner without any criteria to evaluate the quality and integrity of the sampling process. Perhaps the quality and integrity of the sampling process is evaluated based on trust or experience of the practitioner. However without any form of scientific criteria to evaluate the quality and integrity of the sampling process, it is difficult for the sampling process to be scrutinized. The quality and integrity of both the sampling process and laboratory analysis must be scientifically evaluated based on the uncertainty of measurements in line with the monitoring goals/requirements. This presentation discusses the aspects of evaluation of measurement uncertainties associated with groundwater sampling as an important component of quality assessment of groundwater sampling processes. The potential implications of the uncertainties on the final results and their use in decision making is also discussed. The credibility of the decisions made also depends on the knowledge about the uncertainties of the final results

Abstract

For years hydrogeologists have bemoaned the fact the groundwater is often pushed aside in favour of surface water resources being developed for water supply purposes. This is despite the advantages of groundwater being less vulnerable to the impact of drought, generally significantly cheaper to develop and being ubiquitous in character. The intangible character of groundwater was thought to be a major factor in water resources engineers favouring surface water resource development, as well their limited appreciation of the character, exploration, development and management of the resource. But is this really the case? Recent experiences in developing groundwater as an alternative source of water across the Western Cape Province in the face of failing municipal water supplies has highlighted poor communication being a central issue. It was observed that the hydrogeologists had little appreciation of the controls and constraints that govern getting groundwater to the user. Further, their recommendations around the use of groundwater were at times confusing to the uninitiated. Engineers, on the other hand, were found to not adhere to recommended pumping regimes nor appreciate groundwater management requirements. The treatment of groundwater emerged as a constraint that added greatly to the complexity of developing these supplies and requiring ongoing operation and maintenance efforts.

Abstract

The demand on fresh water has increased to such an extend that supply cannot keep up with demand, especially in areas where desalination of seawater is not an option. There is a large gap between the water user, the water supplier and the capacity of the resource/s. The water user sees it as his/her right to be provided with clean water in sufficient volumes to sustain their most basic needs.At the same time people want higher levels of service, especially where sanitation is concerned. The recent droughts in Cape Town and in Port Elizabeth have put significant focus on groundwater and we've seen uncontrolled drilling for groundwater reaching new heights, which is a problem on its own. We can no longer afford not to bring the groundwater user into the water planning cycle, so that the users, on all levels of society, can be educated to understand that the quantity and quality of fresh water (ground -and surface water) is limited and dependent on recharge from rainfall, size of the catchment, topography and all that takes place on the surface. This education must be specific to a target audience and must take into account the existing knowledge and understanding of the user profile. As an example, a case study will be discussed where there are large groundwater users operating within the upper parts of a catchment, followed by municipal abstractions and private abstractions within the central parts of the same catchment. Four profiles of users are therefore present: (1) large-scale irrigation by farmers, (2) large-scale municipal abstractions, (3) private residents and (4) formal / informal settlements, with the latter probably competing for top pot in terms of water use, with the irrigation. They key deliverable of the presentation / paper will be to (1) make people aware of the problem/challenge, and (2) suggest ways to bridge gaps and get all users and service providers to work together to save water and to understand that there are limits to the quantities available.

Abstract

Water scarcity is a global challenge, particular in South Africa, which is a semi-arid country. Due to the continuing drought, appropriate groundwater management is of great importance. The use of groundwater has increased significantly over the years and has become a much more prominent augmentation component to the supply chain especially in rural communities. However, the approach used to develop groundwater resources, specifically in rural areas, can be improved in numinous ways to ensure drilling of successful boreholes that could meet water demands. A recent study done in the Thaba Nchu area focused on an adapted approach, which resulted in drilling successful boreholes that would be able to sustain their augmentation role in the long term. The adapted approach involves (i) a hydro-census that includes local knowledge and focused field observations, (ii) study of aerial photographs and geological maps on a regional scale, rather than on a village scale area, (iii) an optimised geophysical investigation to identify and map geological structures to drill production boreholes, (iv) conducting aquifer pump test to determine an optimum sustainable yield, (v) collecting water samples to determine if water quality is suitable for its specific use (vi) providing a monitoring program and abstraction schedule for each borehole. The adapted approach highlights the following improvements: (i) drilling of new production boreholes during times of bounty to allow for better time management on the project; (ii) including an experienced geohydrologist during planning phases, (iii) including a social component focussing on educating local communities on the importance of groundwater and introducing them to the concept of citizen's science, (iv) establishing a communication channel through which villagers can report any mechanical, electrical, quantity or quality issues for timeous intervention. Through applying these small changes to established components of development of groundwater resources, budgets and time management were optimised and additional communities could be added to the project without additional costs. This approach not only emphasised ways to improve the awareness and potential of groundwater resources, but also affects the economical-, social- and environmental welfare in rural communities.

Abstract

Large parts of the City of Cape Town overlie a significant aquifer. Urban development proceeded without acknowledgement of the importance of this aquifer causing contamination in some areas and a lack of protection of recharge areas. Use of the aquifer for private domestic and industrial purposes has also largely continued unchecked. With the recent drought in Cape Town use of the aquifer dramatically increased, as did the City's understanding that the aquifer is a strategic resource to them. This paper presents the pros and cons of decentralised groundwater use. The current status quo of decentralised groundwater use in Cape Town, from basements to garden irrigation boreholes and to large-scale industrial users is presented, along with an assessment of the impact of the drought on groundwater availability. Recommendations are provided for how best to manage the challenges of decentralised groundwater use.

Abstract

The Two-Streams catchment located in the KwaZulu-Natal Midlands, South Africa has been used as an experimental catchment over the past decade to investigate the impacts of Acacia mearnsii stands on hydrological processes. As part of the ongoing study, the hydrogeology of the catchment was investigated and characterized to understand the impacts of Acacia Mearnsii plantations on groundwater. The hydrological, hydrogeological, hydrochemical and environmental isotope methods were employed in characterizing the hydrogeology of the catchment. The study area is underlain by three geological units: top weathering profile, mainly of clay, which is underlain by weathered shale. Shale is in turn underlain by granite rock. Two hydrostratigraphic units were identified: an unconfined aquifer occurring along the weathered shale and the underlying regional semi-confined aquifer. The regional aquifer is characterised by transmissivity range of 0.15 to 0.48 m2/day, hydraulic conductivity of 0.04 m/day and annual recharge of 31.9 mm. The catchment receives a mean annual rainfall of 778 mm, mean annual evapotranspiration of 802 mm and mean annual stream discharge of 20387 m3. The groundwater and stream samples are characterised by mean specific electrical conductivity of 28.5 mS/m and Ca-HCO3 and Ca-Cl dominant hydrochemical facies. Isotopic values indicate recharge from rainfall with insignificant evaporation during or prior to recharge. Seasonal stream isotope data analysis indicates groundwater as the main contributor of streamflow during dry season. Furthermore, the impacts of Acacia mearnsii trees on groundwater were investigated. Results show that direct groundwater uptake by tree roots from the saturated zone at Two-Streams would not be possible due to limiting root depth. Thus, in instances where the regional groundwater table is not available for direct abstraction by tree roots, trees can have large impact on groundwater by extracting water from the unsaturated zone, reducing recharge to aquifers and baseflow, without having direct access to groundwater

Abstract

The advent of the 'Big Data' age has fast tracked advances in automated data analytics, with significant breakthroughs in the application of artificial intelligence (AI). Machine learning (ML), a branch of AI, brings together statistics and computer science, enabling computers to learn how to complete given tasks without the need for explicit programming. ML algorithms learn to recognize and describe complex patterns and relationships in data - making them useful tools for prediction and data-driven discovery. The fields of environmental sciences, water resources and geosciences have seen a proliferation of the use of AI and ML techniques. Yet, despite practical and commercial successes, ML remains a niche field with many under-explored research opportunities in the hydrogeological sciences. Currently physical-process based models are widely applied for groundwater research and management, being the dominant tool for describing and understanding processes governing groundwater flow and transport. However, they are limited in terms of the high data requirements, costly development and run time. By comparison, ML algorithms are data-driven models that establish relationships between an input (e.g. climate data) and an output (e.g. groundwater level) without the need to understand the underlying physical process, making them most suitable for cases in which data is plentiful but the underlying processes are poorly understood. Combining data-driven and process-based models can provide opportunities to compensate for the limitations of each of these methodologies. We present applications of ML algorithms as knowledge discovery tools and explore the potential and limitations of ML to fill in data gaps and forecast groundwater levels based on climate data and predictions. Results represent the first step in on-going work applying ML as an additional tool in the study and management of groundwater resources, alongside and enhancing conventional techniques such as numerical modelling.

Abstract

The hydrogeological setting of a proposed mine site can significantly influence the viability of the mining venture. The management of groundwater inflows, costs of the dewatering technology, construction and maintenance of storage facilities, discharge strategies and anticipated environmental impacts are vital factors for consideration. It is fundamental to assess the hydrogeological setting at an early stage of the mine life cycle and should involve the collection of sufficient hydrogeological data, conceptualisation of the hydrogeological setting and an assessment of planned mine operations and anticipated impacts. Ambient hydrogeological conditions at the deposit area may be identified by conducting a hydrocensus and utilising existing ore exploration drilling data. Information from the hydrocensus and ore exploration drilling can provide valuable preliminary data on groundwater risks, dewatering and available groundwater resources. Potential groundwater/surface water interactions and receptors sensitive to environmental impacts can be identified during a hydrocensus. Similarly, water strikes and fracture density recorded during exploration drilling provide valuable insight to the subterranean environment. It is also possible to obtain aquifer hydraulic properties through packer testing of exploration boreholes. Geochemical test work on exploration borehole-cores could provide valuable information regarding contamination risks from ore deposit and waste material storage. The installation of piezometers within available and accessible exploration holes that extend below the regional groundwater level can pioneer the collection of monitoring data crucial for consideration during the mine life cycle and provide an understanding of the interaction between hydrogeological units and recharge characteristics. Ultimately, mine operations and associated potential impacts on the surrounding groundwater environment can be simulated with the application of numerical hydrogeological flow and contaminant transport models. The numerical models can simulate the regional groundwater flow system and complexities of the mine environment, the accuracy of which is influenced by the type, spatial and temporal distribution of the data collected. It is accordingly suggested that the collection of hydrogeological data and information during the exploration phase would facilitate the timely conceptualisation of potential groundwater risks and effective planning of hydrogeological investigations required during upcoming phases while assisting in the budget optimisation of these future studies.

Abstract

In South Africa, the use of stochastic inputs in surface water resources assessments has become the norm while this is rarely done for groundwater resources. Studies that have applied multi-site and multi-variate methods that incorporate stochastic generation of groundwater levels are limited. Stochastic based inputs account for uncertainties attributed to inherent temporal and spatial variability of hydrologic variables and climatic conditions. This study applied variable length block (VLB) stochastic generator for simultaneous generation of multi-site stochastic time series of rainfall, evaporation and groundwater levels. In the study, 100 stochastic sequences with record length of 34 years (1980-2013), similar to the historic one were generated. Performance of VLB was assessed by comparing single statistics of historic time series located within box plots of the 100 annual and monthly stochastically generated time series. The statistics used include mean, median, 25th and 75th percentiles, lowest and highest values, standard deviation, skewness, and serial and cross correlation coefficients. Majority (9 out of 10) of the historical statistics were mostly well preserved by VLB, except for skewness. Historic highest groundwater levels were mostly underestimated. Historic statistics below interquartile range (overestimation) is a common problem of weather generators which can be reduced by including additional covariates that influence atmospheric circulation. The generation of multi-site stochastic sequences support realistic assessment of groundwater resources and generation of groundwater operating rules.

Abstract

The City of Cape Town (CoCT) commenced a study into the feasibility of the Table Mountain Group aquifers (TMGA) for augmenting the water supply to the city in 2002. It comprised drilling of exploration boreholes in several target areas and the establishment of a hydrogeological and ecological monitoring network. Due to the prolonged drought and associated water crisis, the CoCT decided to fast-track the TMGA development in 2017. The first wellfield is currently developed within the catchment area of the Steenbras Dam comprising production boreholes targeting the Skurweberg and the Peninsula aquifers of the TMGA. Since groundwater abstraction from the Peninsula and Skuweberg aquifers might have a short-term or long-term impact on aquatic ecosystems (i.e. streams and wetlands) that are linked to the TMGA. As a result, evaluation of the potential impact of groundwater abstraction from this aquifer system requires an understanding of the nature and extent of groundwater dependency of the ecosystems. A variety of data sets and parameters have been measured over the last decade at ecological monitoring sites across the study area, of which two sites are located within the Steenbras catchment that are probably connected to the Skurweberg Aquifer. Recently further boreholes and monitoring sites have been added. This paper describes the various methods used and results of the analysis towards a conceptual understanding and quantification of the groundwater dependency of the selected ecosystems. While groundwater contribution is only one factor in ecosystem functioning, sustainable and adaptive management of the groundwater use must be based on the conceptual model and ongoing monitoring of the ecosystem responses.

Abstract

Groundwater water levels and the ability of aquifers to sustain water have been reportedly on the decline in specific areas in the Northern Cape Province in South Africa. The study area is located in an arid regional with mean annual precipitation of less than 400 mm/a, which is drought prone. The hydrological balances indicated that the required groundwater recharge to balance is at least 20 times less than the expected minimum natural recharge. Further investigation indicated that evapo-transpiration forms +95% of the hydrological balance. The models were very sensitive to evapo-transpiration, which focused the study towards land use and land cover. Research on land cover provided evidence that bush encroachment of especially alien species (e.g. Prosopis and Acacia Millefelera) could be responsible for increasing evapo-transpiration if compared to natural grassy vegetation with infestation levels of 5% to 8% in the study area. The hydrological models indicated that infestation of 2.5 % is sufficient to capture all the rainfall reducing groundwater recharge to zero. The study shows that infestation in combination with a thick soil cover of Kalahari Sand or associated formations provide a buffer for groundwater recharge as the soils have a high soil moisture retention capacity which is ideal for use by plants, especially deep rooted woody species. More detailed investigations are under way to compare present and historical land cover and evapo-transpiration potential to qualify the findings of the initial study. Land management and mitigation of bush encroachment is recommended to ensure the sustainability of future soil moisture and groundwater recharge.

Abstract

Siloam, a village in the Northern province of South Africa (SA) has groundwater reportedly characterised by concentration of fluoride greater than the permissible limit of 1.5 mg/L by the World Health Organization (WHO). In response to reported high incidences (80%) of dental fluorosis in Siloam, sources of fluoride in the groundwater of Siloam village was investigated. Earlier hypothesis suggest that the source of fluoride could be fluorite. Physicochemical parameters were determined using a combined multimeter; while total fluoride (TF) was determined using Ion Chromatograph and Fluoride Ion Selective Electrode. Mineralogy of the rocks and soil in the village was determined using X-ray Fluorescence and X-ray diffraction, respectively. Results revealed that groundwater fluoride concentration ranged from 3.92 to 4.95 mg/L, which are far above the WHO permissible limit and South African National standard. Na-Cl water type was found to be dominant in the water samples which could be due to the heavy weathering of plagioclase present in the parent rocks. TF content of the rocks and soils of the village ranged from 10 to 2000 mg/L. Leachates were obtained by soaking the pulverised rocks and soil in de-ionized water over a period of 24 hours. TF in leachates ranged from 0.27 to 14.88 mg/L and 0.05 to 10.40 mg/L at induced, and non-induced temperature, respectively. Although, previous research hypothesize fluorite to be the possible source of fluoride in the village, this research shows that the main contributors of fluoride to groundwater in Siloam were smectite clays and the muscovite present in the sandstone, Investigation also revealed that the geothermal temperature of groundwater in the area is also a major factor enhancing the release of fluoride from the clay material into the groundwater.

Abstract

Groundwater flow system responses have been understood using derivative analysis. The argument is that the use of derivative analysis derived from pumping test data improves the understanding of aquifer types and curve matching in a hydrogeologic setting. The different aquifer systems encountered in Western Cape Government Business Continuity Programme (WCBCP) of South Africa was used as case study where the analysis of the time versus draw-down derivative plots were applied to validate the aquifer characteristics to explaining the groundwater flow systems. Key findings showed that analysis from the time versus draw-down derivative plots can be used to infer conditions within the wellbore, groundwater flow to boreholes and boundary conditions within the aquifer to provide insights. In addition, results confirmed that the archetypal time vs draw-down responses enabled characterizing the aquifer types and such analysis showed unique responses to the pumping. Lastly, long term operation of boreholes for water supply were ascertained when the analysis was interpreted. The analysis was enhanced when the geological information that was collected during drilling operations, were added to the conceptual understanding of groundwater flow studied aquifer system. However, due to costs implications of conducting long-term aquifer hydraulic pumping tests, deviations from the conventional draw-down responses are expected. In this study, it is suggested that due to complexities associated with heterogeneous flow in aquifer types, it is essential to combine derivative analysis with pumping methods to improve interpretation and assessing long term operation of boreholes for water supply

Abstract

The hydrological cycle consists of several components, with two of the major processes being that of surface water flows and groundwater flows. It has been proven before that these two components interact with each other and are often critical to the survival of the associated users and ecosystems, especially in non-perennial river systems. Non-perennial river systems have a limited number of studies, especially on its link to groundwater and the management of the system. Surface water and groundwater individually contribute to the quality, quantity and distribution of water available and the effect on down gradient users. Understanding these processes would help greatly in managing the non-perennial river/groundwater catchment systems along with its respective ecosystem. The aim is, therefore, to provide an understanding of the groundwater and surface water interactions in the research catchments of Agulhas, Touws and Tankwa-Karoo, and to understand the influence of management decisions related to groundwater use. To achieve this aim, conceptual models will be formulated for the different sites using borehole, geophysics, hydraulic and geochemical data collected in the research catchments. Prediction of the effects of groundwater use on the river systems, and river modifications on groundwater levels, will be done using numerical models to simulate the flow processes and the interactions. With the often strong reliability on groundwater in semi-arid and arid regions to support ecosystems and surface water pools, it is expected that the results will indicate a decrease in river flows (and existence of pools) with an increase in shallow aquifer groundwater abstraction. However, the regional flow of groundwater and surrounding faults and springs may have an influence large enough to counter the expected result.

Abstract

The quality of groundwater is, in part, controlled by the character of the rock in which it is stored and the water - rock contact time. Rainfall (or recharge) is also a contributing factor as the mineralisation of groundwater increases from east to west across South Africa. It is well established that groundwater is more mineralised than surface water, and with most of South Africa's domestic supplies being sourced from dams, municipal water supplies are generally of low salinity. The exception to this is where water supplies are sourced from groundwater - such as in the Karoo and along the West Coast. The assessment of water potability is based on both the South African National Standard 241 and the Department of Water and Sanitation guidelines, with the former being a legal requirement. Previously, SANS 241 had two classes of water with the lower class only being allowed for a limited period. In 2015, Class II water was done away with and only a single class of water is now specified. While this may have been done to conform to World Health Organisation standards, it disregarded the realities of a resource-strapped South Africa where in large parts the municipal water supplies simply cannot meet the SANS241 standard. This paper examines the implications of the SANS 241 standard on efforts to establish emergency groundwater supplies during the drought impacting the Western Cape Province.

Abstract

The mitigation of groundwater impacts related to gold mining tailings disposal within the Orkney-Klerksdorp region was assessed and presented as a case study. The most pressing concern for the facility owners is the potential for pollution of water resources in the vicinity of the mines, especially after mine closure. The key focus of this paper is to describe how methods were applied to characterise the aquifer and keeping the source-pathway-receptor principles in mind. Characterisation also involves lessons learn by comparing pre-tailings deposition and post-tailings deposition aquifer bahviour. Ultimately the process followed in this paper has led to the development of a logical approach to estimate groundwater liability costs in a typical tailings environment. The link between hydrogeology, geotechnical engineering and civil engineering was identified as a critical foundation for the development of a successful groundwater management strategy

Abstract

The purpose of this study was to determine the optimal sampling methods for the analysis of radioactive material in fractured rock aquifers. To achieve this a number of data sets were used which span a 40 year period in and around Beaufort West. Well purging requires the pumping out of stagnant water. This step is crucial as the idle well water may not be representative of the entire aquifer. This step was found to be critical in the studies analysed and had a direct impact on the results. It is necessary to pump out the entire well volume and recommended to pump out at least two well volumes before sampling commences. Samples may also be taken prior to well-purging as a means of checking the effects of purging. Another important aspect for sampling is that of multi-level sampling, particularly in the case of boreholes which feature multiple fracture or aquifer interception points. Prior to sampling, sampling containers should be well washed and cleaned using HCl and rinsed with deionised water. This is done to remove any contaminants which may hinder laboratory analysis. It was found that the multilevel sampling method yielded the best results. Furthermore, the samples stemming from windmills also had good results. The evolution of sampling as a science has improved over the past 40 years, but a fundamental understanding of sampling as a science needs to be incorporated

Abstract

Groundwater monitoring, especially from the end users' point of view, is often considered an add-on, or even unnecessary overhead cost to developing a borehole. Simply measuring groundwater level over time can however tell a story on seasonal rainfall fluctuations as well as the response of an aquifer to the removal of an abstracted volume of water. In this case an artesian borehole of high yield and exceptional quality was drilled in an area of minimal groundwater use because of known poor quality and low yields. The borehole was drilled in two stages with the deeper drilling resulting in significantly higher yields and the artesian flow. Sediment free water, deep artesian water strikes and a lack of flow around the casing led to the conclusion that capping at surface would control the visible artesian flow of 4 L/s. A slight drop in pressure indicated that subsurface leakage may however be occurring. Neighbouring boreholes with automated water level monitoring provided data showing a correlation of drop in water level to the second deeper drilling event. The artesian borehole was yield tested and this too was visible in the water level monitoring data. Hereafter it became apparent that each activity performed at the artesian borehole had an impact on the monitoring boreholes, and that a subsurface leak was causing local depressurization of a semi-confined to confined aquifer. An initial attempt to save the artesian borehole was unsuccessful, resulting in the necessary blocking and abandonment of a high yielding, superior quality borehole. If monitoring data was not available the local drop in water level would never have been noticed with disastrous effect and no evidence for the cause. Simple water level monitoring has averted this and kept neighbourly relations and ground water levels intact

Abstract

The expectation that during yield tests, a borehole will react within the expected framework of the existing numerical models, is often not met within real-world scenarios. This is mainly due to the observation that the Theis solution for confined aquifers, Neuman solution for unconfined aquifer and Barker Generalised Radial Flow Model for hydraulic tests in fractured rocks all include idealised assumptions regarding the physical aspects of a hypothetical. In order to interpret the data from a yield test these methods, along with the Flow Characteristic method for sustainable yield estimates, are commonly used. However, as these assumptions are not always met, the analysis is usually focused on time periods within the test that approximate these solutions. In some cases, the extent to which these assumptions are not met can produce drawdown data that is not well described by the usual analytical models used to analyse this data. This study addresses some of the shortcomings experienced during testing in non-ideal aquifers, as well as briefly describing some tests where small budgets, short deadlines, a lack of information and/or unforeseen circumstances resulted in similar challenges to analyses. This study does not present new solutions to drawdown data analyses, but rather discusses how the mentioned solutions were used during testing to accommodate for the shortcomings experienced.

Abstract

Due to the recent drought in the Western Cape province of South Africa, surface water can no longer meet our current demand of water and as a result groundwater usage has increased. High iron concentration in groundwater is a problem which results in iron encrustation and iron clogging. This results in decreased borehole yields, decreased water quality and expensive treatments to remove iron encrustation or the drilling of entirely new boreholes. From both international and local literature there are two common factors which stand out which is that high concentration of iron in groundwater is a global issue, the second common factor is that the occurrence and influencing factors of high iron concentrations are site specific. Boreholes drilled for drought relief in health facilities across the Western Cape have reported increased concentrations of iron. Understanding of the geology, hydrogeology and hydrogeochemical conditions that cause the increased iron concentrations in groundwater at these specific locations is required. The objectives of this research project are to: 1) Assess spatial and temporal variations in iron and manganese concentrations; 2) Establish site specific processes that control the concentration of iron in groundwater; and 3) model the geochemical processes that impact iron levels in groundwater. These objectives will be achieved through historical groundwater quality data analysis, geochemical modeling, field work where samples will be collected and laboratory analysis of the samples collected. The information provided from this research project will allow for the effective management decisions to be made in terms of iron removal from groundwater and early preventative measures that can be made to ensure iron clogging and encrustation does not occur. The study is currently ongoing and there are currently no results available at this point however, at the time of the conference there will be information ready to share.

Abstract

Brackish groundwater resources could become an option to diversify the water supply-mix in the future when coupled with desalination or other evolving and cost effective water treatment technologies. This paper discusses regulatory and management responses dealing with brackish groundwater in international jurisdictions to form a basis for decision-making in groundwater management in South Africa. Recent literature and research on brackish groundwater was reviewed to reflect on efforts by other jurisdictions (California, Texas - USA) to regulate and manage brackish groundwater and to formulate desirable goals for brackish groundwater management for South Africa. The regulatory responses in international jurisdictions include pollution prevention, permitting, underground disposal control and differentiated groundwater use. The groundwater management responses include adaptive management, optimized groundwater abstraction, demand management approaches, managed aquifer recharge and alternative technologies. Based on the review the following strategic objectives are defined for South Africa: (i) implement responsible brackish groundwater use in areas with low salinity groundwater; (ii) promote brackish groundwater supplies for desalination; (iii) establish rules for the protection of brackish aquifers from activities in the subsurface; and (iv) create regulatory certainty about the use of brackish groundwater resources. There are several beneficial uses of brackish groundwater resources. In the USA and Canada, brackish groundwater is now the norm in unconventional gas development whereas in water-scarce areas, drinking water is being produced by desalination of brackish groundwater. In Texas - USA, municipalities choose to pay for the cost of advanced treatment rather than incur the cost of building additional water transportation infrastructure (dams, canals, and pipelines) or securing additional water rights. Some industries may use brackish groundwater with minimum or no treatment. Untreated, low-salinity brackish water may be used for irrigation, and higher-salinity waters may be used for the cooling of power plants. Groundwater is a public good in South Africa which requires an authorization for its sustainable abstraction, and It is therefore important to stipulate the correct licence conditions for sustainable brackish groundwater. Critical are the conditions for discharging brine concentrate resulting from desalination processes. It is unlikely that apart from the coastal areas, there may be deep saline aquifers to dispose the brine and these areas require detailed hydrogeological studies - this knowledge is currently not available.

Abstract

The groundwater risk map for the Karoo aquifers has been developed by incorporating the major geological, hydro-geological and uranium concentration factors that affect and control the groundwater contamination using GIS-based DRIST model. This work demonstrates the potential of artificial intelligence to produce a map by using various spatially geo-referenced digital data layers that portray cumulative aquifer sensitivity ratings across the Karoo Uranium Province, South Africa. This provides a relative indication of groundwater risk to uranium contamination. The pollution index used in this analysis was the uranium concentration (expressed as ?g/L). The selection of this index was based not only on the fact that it constitutes the main contaminant that occurs naturally in the geology of the study area but also because it is a prime health hazard and its presence in concentrations that exceed the drinking water guidelines is a representative indicator of groundwater quality degradation. The methodology used for assessment of groundwater risk was based on an approach which was modified specifically for assessment of Uranium pollution at a regional Karoo Uranium Province, where the five DRIST maps were integrated to form an intrinsic vulnerability map. The results show that the high risk for contamination of groundwater by uranium covers the central and northern parts of the study area. The southern part is slightly less risky due to a combination of parameter settings which tend to favour attenuation as compared to transport of uranium in the subsurface. This parameter includes; rocks with good chemical attenuation properties, deeper groundwater table, and less yielding aquifers. The results were validated using the area under the curve approach and a high validation value of 0.737 was obtained. Thus, the groundwater risk map developed can be used for regional environmental planning and predictive groundwater management

Abstract

The main purpose of this paper is to present a case study where a water balance concept was applied to describe the expected groundwater safe yield on a sub-catchment scale. The balance considers effective recharge based on local hydrogeology and land cover types, basic human needs, groundwater contribution to baseflow, existing abstraction and evaporation. Data is derived from public datasets, including the WRC 90 Water Resources of South Africa 2012 Study, 2013-2014 South African (SA) National Land Cover and Groundwater Resource Assessment Ver. 2 (GRAII) datasets. The result is an attempt to guide a new groundwater user regarding the volume of groundwater that can be abstracted sustainably over the long-term.

Abstract

The Reconciliation Strategy for the Olifants River Water Supply System (ORWSS) indicated that the surface water resources in the Olifants Water Management Area are already overallocated, and recommended that the potential of the Malmani Subgroup dolomites along the Limpopo and Mpumalanga escarpment as an additional water resource be investigated. The Feasibility Study for Groundwater Resource Development of the Malmani Dolomites within the ORWSS considered among other aspects the hydrogeology, hydrology, artificial recharge potential, groundwater - surface water interaction and wellfield design options. A key aspect of the analysis and study findings was determining the amount of water that can be provided additionally, as the groundwater development was conceived as impacting on and reducing the ORWSS system yield. Hence, the implementation strategy was designed to address this mistrust in the groundwater potential and to allow for increasing the confidence in the yield estimates over time. The implementation strategy identified several possible recipients of the water, influencing the prioritisation of wellfield development. The scheduling of implementation should first address community water supply shortfalls in the area, followed by releases to the Olifants River to cater for environmental requirements and then direct development for bulk water supply schemes. Out of the twelve identified wellfield target zones (WFTZ), eleven are recommended for potential wellfield development. Seven Malmani Subgroup dolomite aquifer WFTZs have high groundwater development potential with proven high borehole yields (>10 l/s) and are recommended for priority full-scale wellfield development, through a phased monitor-model-manage approach. The total proposed groundwater development comprises 48 wellfields with a combined yield of >40 million m3/a. Although several organisations are suitable for implementing the scheme, or parts thereof, the DWS should maintain oversight function to ensure that the several parts of the scheme development are implemented in a coherent manner and in accordance to the implementation strategy.

Abstract

With an increasing population, development of the country and a changing climate, an increased demand for fresh water, coupled with negatively impacted natural water resources, are observed. One impacted component of the water resource may have an impact on another, due to the interaction between water resource components in the water cycle. All water resource components need to be well-managed and protected to ensure their availability and sustainability. Studies on water quantities, flow dynamics, quality, and contamination are essential in this regard. Isotopes are used as a tool in these studies to define the interconnection between different water resource components. The information gained from isotope studies is valuable in the planning of activities in areas where interacting water resource components may potentially be affected. A study in Middleburg comprised a literature review and field investigations at and around a cemetery, as part of a Water Research Commission project on impacts on the water resource from large scale burials. A seasonal wetland is located downgradient of the cemetery, between the cemetery and a stream that flows past the cemetery. In order to assess possible flow pathways from the cemetery to the stream, monthly monitoring of surface and groundwater quality and level fluctuations was carried out on the stream, as well as existing and newly installed boreholes at the site. The water samples were analysed for inorganic constituents, tritium, and stable water isotopes. The isotope results - revealed the comparative influence of rainfall and shallow groundwater contributions to streamflow, while groundwater provides base-flows as the stream levels recede. The depth to groundwater reduced with increasing rainfall, indicating direct recharge. The difference in concentrations of some inorganic parameters in the stream compared to the groundwater at the cemetery revealed the effect of natural attenuation and the wetland acting as a filter to improve the water quality of the shallow interflow.

Abstract

In the following study, the soil and groundwater regime of the Rietvlei wetland near Cape Town are characterised. This has been done by means of logging the subsurface material during the construction of 8 shallow wells, complimented with field observations, and surveying the dug wells. The water stemming from these wells was sampled and analysed for Oxygen 18 and Deterium. Downhole salinity logs of the wells were also undertaken and rainfall samples were analysed for the aforementioned stable isotopes. Results indicate a distinct relationship between elevation and soil structure. Through the use of the water table method, it was found that the relationship between elevation and soil moisture had a direct impact on spatially distributed groundwater recharge on an event basis. Furthermore, higher salinities were found with depth in groundwater in the same wells which had higher recharge values. Isotopic results indicate that groundwater all stems from rainfall, with the exception of Well 8 is influenced by the river due to its proximity to the surface water body. The various water chemistries and soil profiles have a direct impact on the type of flora and its distribution throughout the study area. This study managed to conceptualize the relationship between groundwater, soil profiles and the various plant types surviving in the Rietvlei wetland. Future studies can focus on computer based approaches in order to predict how changes in groundwater characteristics caused by natural or anthropogenic factors would affect other ecohydrological processes within the wetland. These findings can be incorporated in decision making processes concerning groundwater management.

Abstract

The hydrochemical, water stable isotopes of groundwater have been determined around Evander Goldfields Mine in Mpumalanga. Based on the stratigraphy of the study area four major aquifer systems can be identified namely Karoo Supergroup, Transvaal Supergroup, Ventersdorp Supergroup and Witwatersrand Supergroup. Hydrochemical and isotope in groundwater were assessed for Karoo and Witwatersrand Supergroup aquifer systems. The results show that in Karoo, groundwater chemistry evolve in two ways: the shallower recently recharged groundwater depicts Ca-Mg-HCO3 water type and the relatively deeper circulation and older governed by ionic exchange present Na-HCO3 water type. In the study area boreholes around tailing facilities constructed to monitor groundwater in the immediate vicinity of these structures show Na-Cl and Ca-Mg-Cl, and this is highly mineralized groundwater. Water samples collected underground mine workings between 1500 and 2080 mbgl in Wtwatersrand Supergroup aquifer system present Na-Cl water type. All groundwater samples analysed for isotopes ?18O and ?2H plot on and/or close to the Global Meteoric Water and Pretoria Meteoric Water Lines. However, groundwater from the deeper part of the underground workings in the Evander mine plot shifting toward negative values of ?18O in relation to the rest of the groundwater in this study. This fraction of groundwater may originate from precipitation isotopically different from the present day rainfall as suggested by deuterium excess values which are above 21.75?. However, the probability that the shifting of ?18O signature may result from groundwater exchange with CO2 gas has to be considered. Hence, analysis of ?18O and ?13C in groundwater CO2 gas has to be performed in order to clarify the hydrochemical processes evolving groundwater in the study area.

Abstract

This study developed operating rules for groundwater supply from a probabilistic (risk-based) approach. Groundwater supply systems are often operated without relating groundwater yield/availability to demand which makes groundwater resource planning and management challenging and unpredictable. Risk-based approaches for developing groundwater operating rules comprehensively incorporate assurance of supply and also account for uncertainty due to model inputs, model structure and climate variability. A groundwater resource unit (GRU) was delineated and its hydrogeological conceptual model developed. A program for generation of monthly groundwater levels for the GRU was coded in FORTRAN based on the GW-PITMAN model. The model was calibrated using groundwater levels from a neighbouring borehole due to lack of observed representative data for the GRU. Validation was done by establishing the realistic nature of simulated runoff, recharge and groundwater levels. A Variable Length Block (VLB) bootstrapping model was used for simultaneous generation of stochastic inputs (rainfall, evaporation and groundwater levels) of the operating rules model. Operating rules were developed from statistical analysis of 100 base yields for the GRU simulated from 5-year long stochastically generated inputs. The hydrogeological conceptual model indicated presence of faults and diabase dykes which influence preferential flow paths and storage of water in the aquifer. Majority of the historical statistics were mostly well preserved by VLB, except for skewness. Superimposing the cumulative demands on the base yield curves and analysis of percentages of water demands that can be supplied indicated that the groundwater system could not meet the water demands at all times. The operating rule curves indicated that if priority classification is used all water demands are met up to a maximum groundwater level of 25 m. The operating rule curves are therefore expected to improve water supply to both domestic and productive water uses, if they are adequately implemented and hence improve livelihoods.

Abstract

Groundwater levels in E33F quaternary catchment are at their lowest level ever. The impact of climatic variation and increasing abstraction were determined to be the main factor. There are 115 registered groundwater users in E33F and the monthly abstraction volumes are not being measured. There is a need to use land use activities as well as the population to estimate groundwater use. The main objective is to use non-groundwater monitoring data to estimate groundwater use in order to protect the aquifer and ecosystem in general in varying climatic condition. Land use activities information was used to estimate groundwater use in E33F quaternary catchment. The estimated groundwater use volumes were compared to allocated and measured volumes. For domestic groundwater use estimation, population data and an estimation 100 litre per person per day were used. The water requirements for the types of crops being cultivated together with the area (m2) were used to estimate groundwater use volumes for irrigation. The number and type of live stocks were used with the water requirements for each livestock type to estimate the groundwater use volumes. 96 % of groundwater users are using groundwater for irrigation purposes with 9 966 105 m3/a allocated for irrigation. Mining, industries, domestic and livestock are allocated 100 200 m3/a. The estimated groundwater use volume for irrigation is 30 960 000 m3/a, which is three times higher than the allocated volume. Groundwater use volume for domestic use is estimated to be 38 225 m3/a which is higher than the 31 000 m3/a allocated. The total estimated groundwater use volume in E33F is estimated to be 30 998 225 m3/a, which is three times higher than the allocated groundwater use volume of 10 066 305 m3/a. This estimation could be higher as only registered boreholes were used and estimations from mining, Industries and live stocks were excluded due to lack of data

Abstract

Artificial Intelligence (AI) has been used in a variety of problems in the fields of science and engineering in particular automation of many processes due to their self-learning capabilities as well as their noise-immunity. In this paper, we describe a study of the applicability of one of the popular branch of AI (Artificial Neural Network (ANN)) as an alternative approach to automate modelling of one-dimensional geoelectrical resistivity sounding data. The methodology involves two ANNs; first one for curve type identification and the other one for model parameter estimation. A three-layer feedforward neural network that was trained from geoelectrical resistivity data taken at boreholes with geology logs was used to predict earth models from measured data without the need to guess the initial model parameters or use synthetic data as is done with most conventional inversion approaches. The motivation for using the ANN for geophysical inversion is that they are adaptive systems that perform a non-linear mapping between two sets of data from a given domain. For network training, we use the back-propagation algorithm. An example using data from southern Malawi shows that the ANN results outperforms the conventional approaches as the results after adequate training, produce reasonably accurate earth models which are in agreement with borehole log data.

Abstract

Burning of coal for electricity production has resulted in vast amounts of ash being deposited in ash dumps. Rain water and ash water conditioning results in the wetting of ash dumps and if the water retention capacity is exceeded there is a possibility of leaching to soil and underlying aquifers. In this study two different coal ash are used to determine the water retention as excess amount of process water at power stations ash dumps can lead to impeding the desired water balance, which can be critical for maintain various plant processes. The nonlinear relationship between soil water content and matrix suction of a porous material under unsaturated conditions is described by the soil water characteristic curve (SWCC). The SWCC for a given material represents the water storage capability enabling the determination of varying matric suction such as prediction of important unsaturated hydraulic processes including soil permeability, shear strength, volume change with respect to the water content changes. This paper presents an alternative, cost effective and rapid method for measuring and subsequent estimating of the soil-water characteristics of any soil type. Several methods are available to obtain the measurements required for defining soil-water characteristics. However, obtaining the required measurements for a SWCC is generally difficult since there is no laboratory or field instrument, capable of measuring a typical complete plant available water suction range accurately. Due to high methodological effort and associated costs of other methods, a simplified evaporation method which was implemented in the HYPROP (Hydraulic Property analyzer, UMS, 2012) becomes a possible alternative. It relies on the evaporation method initially proposed Schindler (1980). A typical work range for a HYPROP system is 0 to 100 KPa as read out from the two high capacity tensiometers installed at different heights within a saturated sample column. For a dry coal ash dump to be optimally used as sinks, input water applications should be matched with evaporation rates and capillary storage. This will ensure the moisture storage of the ash dump is not exceeded and consequently avert leachate generation at the base of the ash dump. The field capacity of waste materials is of critical importance in determining the formation of leachate in landfills which in this case is the coal ash dump facility. It is the field capacity limit when exceeded which give rise to leachate generation consequently promoting a downward movement of generated leachate.he study found that it is possible to use the Hyprop together with an empirical based fitting model to define a complete SWCC along a dewatering path. The study found the Brooks-Corey model as the suitable representative of the Hyprop measured data, confirmed by AICc and RMSE analysis. The Brooks-Corey estimated retention function parameters within +/- 1% error. A mean value of 35.3% was determined as the water retention or field capacity value for Matimba Coal ash. If the ash dump is operated in excess of this value, chances of groundwater pollution are high.

Abstract

Drilling of five shallow (300m) boreholes was undertaken by the Council for Geoscience at Beaufort West. This was to characterise shallow aquifers and to determine the possible deeper aquifers linked to dolerite sills respectively. Furthermore, to determine the interconnectivity between shallow and deep aquifers. The five shallow boreholes B01H_BW, B02H_BW, B03H_BW, B04H_BW and B05H_BW have depths of 151m, 169m, 151m, 169m and 169m respectively. B02H_BW is currently used as a municipal production borehole and has produced volume of more than 134ML since inception February 2018, whilst the others are used for monitoring. Additionally, the two deep monitoring boreholes, R01-BW and R02-BW have depths of 1402m and 517m respectively. The seven boreholes drilled intersected the Poortjie Member, Abrahamskraal Formations (deep boreholes), Waterberg Formation and Tierberg Formation (R01_BW). An east-west striking dolerite sill that is dipping northwards was encountered during the drilling of the deep boreholes. Boreholes closer to this sill showed more brecciation and generally have a high yield, however, during drilling and pumping test there was no indication of water inflow related to the sill. Water strikes in brecciated rock were concentrated in borehole B03H-BW and reduce northward in borehole B02-BW and more rapidly southward in borehole B04H-BW. All the drilled boreholes except R01-BW that was not yielding enough were tested for aquifer parameters and sustainable yields. Interconnectivity between R02-BW and B04H-BW was confirmed when a drawdown response was observed in B04H-BW during pumping of R02-BW. The flow rate encountered in the boreholes indicates a strong yield in boreholes associated with the brecciated rock (B02H-BW, B03-BW, B04H-BW and R02-BW). Findings indicated that these boreholes are drilled in the same unconfined aquifer where the main water strikes are encountered on the contact between the Poortjie Member and the Abrahamskraal Formation.

Abstract

In the wake of the ongoing water restrictions in South Africa, the issue of groundwater potential for drought relief has been debated on many environmental and socio-economic platforms, nationally. Consequently, the development of groundwater and its related vulnerabilities has become a key topic to the decision makers and stakeholders. Currently, the recruitment of water professionals into government and private water sectors adds substantial value to understanding the importance of protecting this precious resource. This has allowed the monitoring of groundwater to gain ever increasing momentum. Groundwater monitoring has become an essential scientific tool for role-players to achieve robust and verifiable data used for modelling aquifer potential and vulnerability to pollution and over-abstraction. The data is generally sourced from various hydrogeological and environmental investigations which include groundwater development, vulnerability assessment and remediation projects. Groundwater and environmental consulting firms are tasked with imperative roles for implementing groundwater monitoring programmes to the ever growing industrial, commercial, agricultural and public sectors in South Africa. However, groundwater monitoring data, especially in the private sector, are reliable but remains mostly inaccessible due to confidentiality clauses. This does limit our accuracy and comprehensive understanding for determining aquifer potential and vulnerability risks at large. The conceptualisation and modelling of vast monitoring datasets has been recognised as an important contributing factor to enhance groundwater sustainability. This research emphasises the significance of groundwater monitoring for development, protection and remediation of aquifers. Comparing monitoring results from typical sites and methods, provides scientific validation to support good governance of water. Deterioration of groundwater potability in the sight of an existing drought can have irreversible environmental and economic implications for South Africa.

Abstract

The hydraulic parameters of heterogeneous aquifers are often estimated by conducting pumping (and recovery) tests during which the drawdown in a borehole intersecting the aquifer is measured over time, and by interpreting the data after making a number of assumptions about the aquifer conditions. The interpreted values of the hydraulic parameters are then considered to be average values that represent the properties of the bulk aquifer without taking into account local heterogeneities and anisotropies. An alternative and more economic approach is to measure streaming potentials in the vicinity of the borehole being tested. The streaming potential method is a non-invasive geophysical method that measures electrical signals generated by groundwater flow in the subsurface through a process known as electrokinetic coupling. This method allows data to be recorded at a high spatial density around the borehole. The interpretation of streaming potential data in terms of aquifer hydraulic parameters is facilitated by a coupled flow relationship which links the streaming potential gradient to the hydraulic gradient through a constant of proportionality called the electrokinetic coupling coefficient. In the current study, field measurements of streaming potentials were taken during the pumping and recovery phases of pumping tests conducted at two sites with dissimilar geological and geohydrological conditions. The recorded streaming potential data were interpreted by calculating the hydraulic head gradient from the streaming potential gradient, and by using the potential field analytical solution for the transient mode, which relates the streaming potential field directly to the average hydraulic conductivity. Hydraulic conductivity values estimated from the streaming potential method were of the same order as values determined from the analysis of drawdown data, with a relative error of 0.2. This study demonstrates that the streaming potential method is a viable tool to compliment pumping tests and provide a spatial representation of the hydraulic parameters.

Abstract

The aim of the following study was to characterise the soils of Sutherland, located in the Northern Cape of South Africa. This was completed in order to shed light on possible pathways for infiltration and understand the ultimate impact on groundwater resources. Therefore, the relationship between the soil characteristics and infiltration was explored. To achieve this, field work was conducted whereby soil profiles were exposed in order to examine the subsurface characteristics of the soil and map the soil types. Thereafter, infiltration tests were taken randomly across the terrain in order to determine the in-situ properties of the soils in the region. Dye tracer tests were conducted on two plots of 1m2 within the study area, to determine the preferential flow paths and heterogeneities within the area. Field observations, as well as dye tracer tests, indicate a low clay content at the surface. This could be attributed to high wind velocity. Finally, it is shown that local river beds are hydraulically conductive due to the coarse nature of the underlying gravel. Therefore these strips of land need to be protected in order to avoid possible contamination of the already limited groundwater supplies in the region.

Abstract

The complexity of real world systems inspire scientists to continually advance methods used to represent these systems as knowledge and technology advances. This fundamental principle has been applied to groundwater transport, a real world problem where the current understanding often cannot describe what is observed in nature. There are two main approaches to improve the simulation of groundwater transport in heterogeneous systems, namely 1) improve the physical characterisation of the heterogeneous system, or 2) improve the formulation of the governing equations used to simulate the system. The latter approach has been pursued by incorporating fractal and fractional derivatives into the governing equation formulation, as well as combining fractional and fractal derivatives. A fractal advection-dispersion equation, with numerical integration and approximation methods for solution, is explored to simulate anomalous transport in fractured aquifer systems. The fractal advection-dispersion equation has been proven to simulate superdiffusion and subdiffusion by varying the fractal dimension, without explicit characterisation of fractures or preferential pathways. A fractional-fractal advection-dispersion equation has also been developed to provide an efficient non-local modelling tool. The fractional-fractal model provides a flexible tool to model anomalous diffusion, where the fractional order controls the breakthrough curve peak, and the fractal dimension controls the position of the peak and tailing effect. These two controls potentially provide the tools to improve the representation of anomalous breakthrough curves that cannot be described by the classical-equation model. In conclusion, the use of fractional calculus and fractal geometry to achieve the collective mission of resolving the difference between modelled and observed is explored for the better understanding and management of fractured systems.

Abstract

A geoscientific research project is underway in the Western Karoo Basin near Beaufort West, South Africa. This area has been earmarked for possible gas exploration. The aim of the project is to improve the understanding of the deeper aquifer systems of the Karoo Basin to better predict potential impacts of geo-resource exploration activities on the deep groundwater systems. This paper reports on the airborne and ground geophysical surveys that were conducted in the study area to gain insight into the deep structural geology and its possible association with aquifer systems. Geophysical methods that were used in the investigations include: 1) the airborne magnetic method was employed to detect and delineate non-outcropping dolerite sills and dykes, as well as to map geological structures of regional extent, and 2) the deep-probing magnetotelluric (MT) technique was used to map conductivity contrasts at large depths that could be associated with prominent geological structures. The results of the geophysical surveys showed that the airborne magnetic method was very effective in mapping intrusive magmatic bodies and other major geological structures. The magnetotelluric results indicated the presence of very resistive layers that appear to be associated with dolerite intrusives. Furthermore, the vertical displacement of a conductive zone indicated the possible presence of large-scale faulting. Based on the results of the airborne geophysical investigations, two investigative boreholes were drilled at selected positions to depths of 516 m and 1 402 m to obtain information on the subsurface geological and geohydrological conditions, and to constrain the interpretation of the airborne geophysical data. Downhole geophysical surveys were conducted on these boreholes to obtain in situ geotechnical and structural information. The results of this project show that the combined use of airborne and deeper probing geophysical methods can greatly contribute to the understanding of the deep geological and geohydrological conditions in the Karoo Basin. The approach can be further utilised for similar investigations of other Karoo satellite basins in South Africa and neighbouring countries

Abstract

The Western Cape region in South Africa is currently experiencing its worst drought since 1904. As a result, the City of Cape Town (CoCT) implemented emergency response projects to augment water supply through desalination, re-use of treated effluent and groundwater abstraction from several groundwater systems. Amongst the targeted aquifers, the Cape Flats Aquifer (CFA) presents unique challenges and opportunities for abstraction and managed aquifer recharge (MAR). The CFA is a coastal unconfined primary aquifer within the urban and peri-urban environment. As such it is well situated to take advantage of enhanced recharge from treated effluent and urban stormwater. MAR is currently being tested and implemented with a three-fold purpose: (1) create hydraulic barriers against seawater intrusion and other contamination sources, (2) protect groundwater dependent wetlands and RAMSAR sites and (3) increase storage to enhance resilience to drought. Due to local hydrogeological characteristics and a high demand for open land, in the short term, high quality treated effluent will be injected directly through boreholes. Numerical modelling has supported siting and quantifying necessary injection rates. Current estimates indicate that available treated effluent will increase sustainable yields from the aquifer two-fold, as well as providing an additional storage volume equivalent to 2 to 3 years abstraction. In the future this is expected to be complemented with the re-design of urban water drainage to further enhance the recharge of stormwater. Given the time-constraints of an emergency response project, long-term testing and study of the system to support design and implementation have been significantly reduced and had to be replaced by a 'learn by doing' approach. We aim to present the on-going challenges of implementing MAR to complement an emergency response, as well as an overview of the scheme, new data and insights gained through the process.

Abstract

A hydrogeochemical analysis of multiple samples stemming from two fractured rock aquifers in the Karoo geological formation of South Africa was undertaken. The samples were taken using various sampling methods in numerous locations over varying time frames. The ion error balance for the groundwater samples from the previously mentioned secondary aquifers is further analysed. Graphical representation of the data, which includes a piper plot, gives insight into the groundwater geochemistry. Conclusions drawn highlight the precautionary measures to take into account when sampling in fractured rock aquifers in a South African context. The future recommendations include suggestions related to the entire chain of sampling in the context of the theory of sampling and measurement uncertainty for fractured rock hydrogeology in particular.

Abstract

The geographic positioning of the Western Cape results in a Mediterranean climate - receiving majority of its rainfall during the winter months. A demand on the water supply throughout the year is typically met by storing water from winter rainfall in large dams. The Western Cape experienced a significant drought between 2015 and 2019. As a result, the supply dams have not been filled to capacity and drastic water restrictions had to be implemented. In the search for alternative water sources, groundwater exploration became a priority. Groundwater development projects were implemented rapidly in attempt to alleviate the implications caused by severe water restrictions and ultimately prevent running out of water. As a local groundwater institution, GEOSS got involved in several fast-tracked groundwater development projects for Department of local government, local municipalities, as well as other industrial and agricultural corporations. For obtaining the required water volumes, alternative measures were implemented. Previously under developed aquifers were targeted. In certain instances, in order to target the Table Mountain Group Aquifer (TMG), horizontal exploration drilling was conducted. The results of exploration and drilling yielded valuable learnings in terms of relevant hydrostratigraphy within the study areas. Additionally, there were learnings in terms of managing projects of this nature. In fast-tracked projects, careful management of the contractors, data collation (and storage) and public perception is critical to the success of the project. In this paper on water supply development for Municipalities, the various components of groundwater development are detailed along with relevant learnings from the recent emergency drought response measures.

Abstract

The groundwater quality in semi-arid aquifers can be deteriorated very rabidly due to many factors. The most important factor affecting the quality of groundwater quality in Gaza Strip aquifer is the excess pumping that resulting from the high population density in the area. The goal of this study to investigate the future potential deterioration in groundwater salinity using scenario analysis modeling by artificial neural networks (ANN). The ANN model is utilized to predict the groundwater salinity based on three future scenarios of pumping quantities and rates from the Gaza strip aquifer. The results shows that in case the pumping rate remains as the present conditions, chloride concentration will increase rapidly in most areas of the Gaza Strip and the availability of fresh water will decrease in disquieting rates by year 2030. Results proved that groundwater salinity will be improved solely if the pumping rate is reduced by half and it also will be improved considerably if the pumping rate is completely stopped. Based on the results of this study, an urgent calling for developing other drinking water resources to secure the water demand is the most effective solution to decrease the groundwater salinity.

Abstract

A conceptual hydrogeological and numerical groundwater flow modelling study is being undertaken around and within the proposed ESKOM Thyspunt Nuclear Site, located 120 km west of Port Elizabeth. The study aims to improve the understanding of the prevailing hydrogeological condition around the Thyspunt area. The area is characterized by folded and jointed geological conditions. The local geology comprises the Table Mountain Group (TMG) and the Bokkeveld Group rocks of the Cape Supergroup, and Quaternary to recent sand deposits of the Algoa Group. The study area receives mean annual precipitation (MAP) of 922.6 mm. The mean annual estimated evapotranspiration is 821 mm and the average annual recharge rate estimated using the Water Table Fluctuation method is about 71 mm. A robust conceptual hydrogeological model is developed through detailed aquifer characterisation including pumping test analyses, determination of groundwater occurrence, storage, and flow, hydrogeochemical and environmental isotope analyses. Groundwater occurs within intergranular of the Algoa Group and fractured quartzitic aquifers of the TMG. The depth to groundwater ranges from 4.5 to 28.9 m below ground level (b.g.l.) and though the local groundwater flow is complex, the general groundwater flow direction is from west to east, towards the Indian Ocean. The upper unconfined intergranular Algoa aquifer and the deeper semi-confined fractured TMG aquifer are characterised by wide range of hydraulic properties, including aquifer thickness (2.2 - 22.0 m and 18.0 - 138 m), hydraulic conductivity ( 4.5 - 19.1 m/d and 8.9x10-3 -1.58 m/d), transmissivity (108.3 - 275 m2/d and 0.4 - 44.0 m2/d), specific yield (1.5x10-2 - 0.1) and storativity (5.0x10-5 - 5.9x10-3), respectively. The main hydrochemical facies of groundwater in the shallow Algoa is Ca-Mg-HCO3 type and groundwater circulating in the deep TMG aquifers are Na-Cl type. Environmental isotope signatures (?2H, ?18O) results indicate groundwater - surface water interactions

Abstract

Hydrogeological mapping was first attempted in Kuruman River Catchment, Northern Cape Province, South Africa. The main geology underlying the area of study includes sediments of the Kalahari Group, limestone and dolomite of the Transvaal Supergroup, lavas of the Ventersdorp Supergroup, and Archaean granite and gneiss. The main objective of this study was to produce hydrogeological maps on a scale of 1/100 000. Demarcation of different aquifer types was done by analyzing factors that control groundwater occurrence. These factors include lithology, geological features such as fault and lineaments, groundwater levels, and groundwater chemistry. Four types of aquifers were identified: o - Intergranular aquifer, associated with alluvial and pluvial deposits. o - Intergranular and fractured aquifer, associated with weathered igneous and sedimentary rock. o - Fractured aquifer, dominated by basal formations. o - Karst aquifer, associated with the dolomitic formations. The groundwater quality in the four demarcated aquifers was assessed to determine the current groundwater status. Groundwater chemistry was measured by collecting groundwater samples from boreholes. Physical parameters such as pH, temperature and electrical conductivity were measured in-situ using an Aquameter instrument. The samples taken were analysed at MINTEK laboratory using Inductively Coupled Plasma Mass Spectrometry, Ion Chromatography, and Spectrophotometer for cations, anions and alkalinity respectively. The results obtained indicated sodium chloride water type in fractured aquifer, while calcium carbonate water type was identified in intergranular aquifer, karst aquifer, and intergranular and fractured aquifer. In conclusion, high concentration of Nitrate, Magnesium, and Calcium was seen in all the four aquifers. High concentration of nitrate is due to stock farming, whereas high concentration of Magnesium and Calcium is due to geology. Moreover, high concentration of mercury due to mining activities was picked in intergranular aquifers, karst aquifers, and intergranular and fractured aquifers.