Conference Abstracts

Abstract

It has become increasingly apparent that understanding fractured rock mechanics as well as the interactions and exchanges between groundwater and surface water systems are crucial considering the increase in demand of each in recent years. Especially in a time where long term sustainability is of great importance for many water management agencies, groundwater professionals and the average water users. Previous callow experience has shown that there is a misunderstanding in the correct interpretation and analyses of pumping test data. The fracture characterisation (FC) method software provides a most useful tool in the overall understanding of a fractured rock aquifer, quantification of the aquifer’s hydraulic (flow regime and flow boundary conditions) and physical properties, only if the time-drawdown relationships are correctly interpreted and when the theoretical application principles are applied. Interpretation is not simply a copy and paste of the aquifer test data into the software to get a quick answer (especially when project time constraints are considered), however, recent experiences with numerous field examples, required intricate understanding of the geological environment, intended use and abstraction schedules coupled with the academic applications on which the software was based for correct interpretation.

Through the application of correct interpretation principles, a plethora of flow information becomes available, of which examples will be provided in the presentation itself. By achieving this, flow can be conceptualised for inputs into a conservative scale three-dimensional numerical flow model and calibrated based on measurable data in a fraction of the time of a conventional regional model. Although higher confidence levels are achieved with these practical solutions, monitoring programmes are still required to provide better insight of the aquifer responses to long-term abstraction and recovery.

Abstract

Complementary use of electromagnetic frequency domain and electrosiesmic geophysical exploration methods in groundwater exploration in Zimbabwe.
Joseph M Zulu, Josrum Enterprises No. 129 A Fort Street, Albion Flats, 2nd Floor, Office Suite 5
Room 3, Bulawayo, Zimbabwe. Email Address: [email protected].
Abstract
Geophysical survey methods and divining are commonly used in groundwater exploration. In view of the current costs of drilling boreholes and fear of drilling a dry borehole, most people prefer the use of geophysical survey methods to have their boreholes sited. Some prefer the use of diving methods for initial siting and then confirmation of the identified site using geophysical survey methods. The key principle being complementarity of the methods to confirm the presence of water at the identified site. Electrical resistivity method and electromagnetic frequency domain methods are popular in ground water exploration in Zimbabwe, with electrical resistivity being the method of choice by many investigators. A new approach in groundwater exploration is proposed where complementarity of geophysical methods is exploited. A complementary approach of using geophysical methods in conjunction with geology, where two methods are used in investigating a site is proposed. In the study the latest technology in groundwater exploration, electrosiesmic survey method was used to complement the electromagnetic frequency domain method in various geological environments. Electromagnetic profiles were carried out on the target areas. Inversion was done on the collected and results presented as a pseudo section. Anomalies identified were further investigated using electrosiesmic sounding. The results of the sounding were presented in the form of a sounding curve. The subsurface layer thicknesses were calculated using forward modelling assuming the typical seismic velocity values of waves generated when passing through geological formations in the areas under investigation. The geology of areas studied include granite, greenstone, Kalahari sands, sandstones, mudstones and basalt of the Karoo stratigraphy. The approach produced impressive results. High yielding borehole sites were identified and successfully drilled in areas where it had been accepted that it was difficult to get water or in areas where it had been accepted there was no groundwater. Comparison of driller's log with models generated from geophysical survey results was also done.
Key words: electromagnetic, electroseismic, geology, complementarity, groundwater.
I acknowledge that this work has not been published elsewhere.

Abstract

Fine ash is a by-product generated during coal combustion and gasification. It is often disposed of as slurry and stored on tailings dams over long periods of time, where it is exposed to weathering. Weathering causes soluble ions to go into solution and to be transported along preferred pathways through the tailings dam. This study was conducted to assess the leaching behaviour of fresh and weathered fine ash and to evaluate the impact on the underlying aquifers. A kinetic test was conducted over 21 weeks to analyse the leachate composition of progressively-aged fine ash and to calculate the release rates for major ions and trace metals of environmental concern. The leachate composition was compared to the groundwater composition of the underlying aquifers to assess the environmental impact of long term ash leaching. The study showed that the release rate of Ca decreased with increasing depth and age of the fine ash. The release rate of Mg, Na, K, Mo, V, Ba, Cr and Mo increased slightly between 22 m and 28 m in the tailings dam. Aluminium had a decreasing release rate from 28 m depth onwards. It was concluded that fine ash leaching influenced the water composition of the underlying aquifers because similarities were observed in the water type trend. The shallow aquifer south of the tailings dam contained Ca/Mg/SO4/Cl/NO3 water with a significant increase in Ca, Mg, Na, Cl and SO4 over time. These ions were expected to be found in the pollution plume due to their high release rate observed in the fine ash. The deeper aquifer northeast and south of the tailings dam showed a reverse trend of decreasing Ca, Mg and NO3 with time. This is possibly due to decreasing release rates in the aging fine ash and due to the cation exchange capacity (CEC) of the aquifer retarding the movement of Ca and Mg in the pollution plume. The shallower aquifer northwest of the tailings dam showed a decrease in Ca and Mg but an increase in K, while the water composition of the deeper aquifer increased in Ca, Mg, Na, K and Cl. This indicates that the pollution plume moved from the shallower to the deeper aquifer and that most of the Ca and Mg content in the fine ash has been leached from the tailings dam after more than 30 years of storage. The study confirmed that leaching of elements from the fine ash tailings dam had a negative influence on the underlying aquifers and that the clay lining was not sufficient in retaining the leachate.

Abstract

Groundwater is often used as an alternative source of drinking water in many places of the world mostly in rural areas. There is a perceived claim that groundwater is clean and safe. This study was carried out to assess the quality of various groundwater sources in the Vhembe District of South Africa. Questionnaires were distributed to residents of the area to evaluate the water use practices. Water quality indices were employed to estimate the usefulness of the groundwater water resources. Heavy metals and major ions were analysed using ICP-MS. E. coli and total coliforms were determined using membrane filtration method. Health risk of the heavy metals in the water was estimated using standard protocol. The results of the study showed that most of the metals complied with the South Africa National Standards. Some of the anions exceeded the recommended limit. Majority of the groundwater sources were fit for other uses except drinking due to the levels of E. coli determined. Sources of contamination determined were both natural and anthropogenic. Adequate monitoring of groundwater resources is recommended to avoid possible risk to public health.

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 International Association of Hydrogeologists and UNESCO's International Hydrological Programme have established the Internationally Shared (transboundary) Aquifer Resource Management (ISARM) Programme. This multiagency cooperative program has launched a number of global and regional initiatives designed to delineate and analyze transboundary aquifer systems and to encourage riparian states to work cooperatively toward mutually beneficial, sustainable aquifer development and management. The Stampriet Transboundary Aquifer System was selected as one of the three case studies funded by UNESCO. The Stampriet Aquifer System is located in the arid part of the countries (Botswana, Namibia and South Africa) where groundwater is a sole provider for water resource. The area is characterised by the Kalahari (local unconfined aquifer) and Nossob confined aquifer

Abstract

The availability of freshwater is one of the major development challenges that South Africa faces. South Africa is a water-scarce (semi-arid) country with rainfall distributed unevenly and away from the centres of major developments. The rainfall is tied to seasonal cycles that drive us repeatedly between floods and droughts. This paper serves to study the groundwater chemistry in light of the uranium mining that precedes shale gas fracking in the Karoo Uranium Province. The aim is to have groundwater baseline chemistry assessment before mining commence in order to be able to track mining effect on groundwater in the future. A total of 128 samples are dealt with in this work, 112 collected from groundwater, 9 collected from springs and 7 extracted from a database. The samples were analysed for physical parameters, cations, anions and metals. Redox potential was also determined as it plays a pivotal role because it controls the availability and form of uranium in a solution. Uranium is a radioactive actinide naturally occurring in the area. Therefore, this assessment will be crucial in order to understand how changing redox and pH conditions affect uranium solubility and to estimate the extent of uranium transport by water during and after mining. The effects of the redox potential and pH on uranium mobility have been examined in this work by means of computer modelling by using the Geochemist’s Workbench (GWB) 11.0. The composition of the water used for modelling resembled that of a typical bedrock groundwater of Karoo Uranium Province. The simulations were carried out under different redox potentials at different pH levels in the presence of ferrihydrite, dissolved organic matter and carbonates/bicarbonates to include the effects of uranium adsorption. The results show that the redox potential at which the uranium mineral (uraninite) dissolves varies depending on the pH of the groundwater.

Analysis of the simulation results indicated that the dissolution of uraninite takes place at a lower Redox condition with increasing pH (alkaline pH condition). This means higher redox conditions are needed for the dissolution of uraninite at low pH. Moreover, it is further concluded that the adsorption of uranium to ferrihydrite and carbonates is important at pH 6-10 and pH 5-8 respectively, which therefore play an important role in controlling the mobility of uranium in the modelled groundwater.

Abstract

Changes to South African water law and policy since the mid-90s have promoted integrated water resource management (IWRM) and the wider application of the principle of subsidiarity (decentralization), underpinned by the Constitutional emphasis on equity, human rights and redress. New water management organisations aim to promote equity, universal access to water, economic prosperity and gender equality but the reality, especially for groundwater, is less inspiring. The Water Act of 1998 envisages new organisations including Catchment Management Agencies (CMAs), Water User Organisations (WUAs) and Water Service Authorities (WSAs), but in many cases these organisations have inadequate capacity or do not exist at all. Only two of the nine (formerly nineteen) CMAs have been formed in more than fifteen years, and neither is yet financially self-reliant. The onerous process necessary to found a WUA and other disincentives have meant that fully-fledged WUAs as envisaged by the Water Act are rare. Hydrogeologists are unusual at Water Service Authority level, and the Department of Water and Sanitation (DWS) still assesses most groundwater resources. This has stoked argument between DWS and WSAs over long-term sustainable municipal water supplies. Our mandated organisations are not delivering the outcomes for groundwater that policy makers envisaged. Municipalities campaign for surface water instead of groundwater, yet groundwater is still the mainstay of rural water supply and has the most promise for underserved areas. Intractable problems with operation and maintenance are wrongly blamed on the primary groundwater resource, or on "shortages" of one kind or another. There is a need to emphasise function and outcomes rather than trust that these will follow automatically once "the right" organisations are in place. A hybrid of top-down expertise with a genuine focus on local outcomes is called for. We currently pay a considerable opportunity cost for delays, turf-wars and finger pointing - including reputational damage to groundwater as well as less reliable water supplies for the poorest South Africans.

Abstract

Evidence suggests that physical availability of groundwater may be only one of many factors in determining whether groundwater-based rural water supply schemes in South Africa are reliable or "sustainable". Other factors include budgetary constraints, community preferences, policy decisions, operation and maintenance procedures, and the availability of skilled staff. These factors and others combine to create "complex problems" around the issue of rural water supplies that require a multidisciplinary approach if they are to be effectively resolved. This work is an on-going part of Water Research Commission Project K5/2158, “Favourable Zone Identification for Groundwater Development: Options Analysis for Local Municipalities”, due to be completed in March 2014.

Abstract

The pollution of water resources has become a growing concern worldwide. Industrial, agricultural and domestic activities play a pivotal role in water resources pollution. The challenge faced by pollution   monitoring   networks   is   to   understand   the   spatial   and   temporal   distribution   of contaminants. In hydrology, tracers have become a critical research tool to investigate surface water and groundwater transport dynamics. Synthetic DNA (deoxyribonucleic acid) tracers are being used in hydrological research to determine source areas, where uniquely labelled DNA from each source area  is  identified.  The main  objective  of the  study  was to  determine  the mass  balance of  the synthetic DNA tracer in surface water streams. Furthermore, to gain knowledge on DNA adsorption and decay and determine whether DNA behaves as conservative tracer in the surface water streams. Understanding the adsorption and decay characteristics of synthetic DNA tracers may promote its robustness in hydrological research. In this study, field injection experiments using synthetic DNA were  carried  out,  the  DNA  tracer  was  injected  together  with  sodium  chloride  (salt)  and deuterium as conservative reference tracers. The purpose was to compute DNA mass balance calculations with reference to the two conservative tracers. In this study two different DNA markers were used, namely T22 and T23. Additionally, with each injection experiment a field batch experiment was carried out to determine DNA loss characteristics on the field. From our study, the DNA loss between the injection point and the first measurement was greater than 90%. Therefore, it was important to conduct additional laboratory batch experiments to explain DNA loss characteristics. However, the issue of the initial DNA loss remained unresolved. Laboratory batch experiments results allow us to conclude the following: the type of material used, filtering, ion concentration and water composition reduced DNA concentration. Moreover, initial DNA losses occurred and not DNA decay. From our experiments we concluded that DNA can be used for long-term tracer experiments, subsequently, limiting synthetic DNA mass balance determination of synthetic DNA as it is a reactive. Overall, we can conclude that DNA does not behave as a conservative tracer.

Abstract

The rainfall situation in the Western Cape became a focal point in 2015; 2016 and 2017. The rainfall in 2015 was half the long term average; in 2016 it was still below the long-term average and in 2017 it was again about half the long-term average. In 2018 the rainfall was better and was about the same as the long term average. These consecutive years of low rainfall were really problematic and with the declaration of the "Day Zero" campaign the media brought the plight of the City of Cape Town into the global headlines. However it was not only the City of Cape Town that was under dire stress but the whole of the Western Cape Province (and beyond). The neighbouring District Municipalities (DM) also embarked on frantic groundwater development and augmentation programmes. GEOSS South Africa (Pty) Ltd was fortunate to be involved in the DMs surrounding the City of Cape Town.

This presentation focusses more on the groundwater aspects per se rather than the technical; aspects of boreholes; pumps etc, with specific reference to case studies including the Sandveld; Saldanha Bay Local Municipality and the Stellenbosch Local Municipality (specifically the Franschhoek area). The Sandveld (which is within the Berg River District Municipality) has a significant agricultural sector and 25 years of regional groundwater monitoring indicates that even with significant groundwater abstraction for the agricultural activities within the area, the groundwater volumes are robust enough to support further development of groundwater to meet the increasing water requirements for the town supply of Graafwater and Lamberts Bay. This expansion is currently underway.

The West Coast District Municipality (specifically the Saldanha Bay Local Municipality) committed significant resources to groundwater development in the times of the drought. The Langebaan Road Aquifer wellfield was expanded with additional production boreholes and a new wellfield, known as the Hopefield Wellfield was also fully developed and equipped with all infrastructure in place. The wellfields have also set up to implement Managed Aquifer Recharge. Although these schemes are not yet operational, the groundwater levels held up well during the drought, indicating these wellfields should play a major role in times of future drought. Groundwater within the Franschhoek area (Winelands District Municipality) is utilized by many sectors and from detailed and long term monitoring the drought had little impact on the resources supporting the development of groundwater supply schemes for Municipal augmentation. From widespread work in the Western Cape Province it is evident that the drought had little impact on the groundwater levels of the region and it bodes well as a resource to be utilised in times of severe stress, so long as it is properly authorised, monitored and managed.

Abstract

The Saldanha / Langebaan area is expanding at a significant rate, increasing the water demand for the area. The expansion comes from the industrial, residential and tourism sector. In addition there are economically viable deposits of silica and phosphate in the area. Ecosystem functioning in the area is also to a degree dependent on groundwater. All of these factors require an improved understanding of the geohydrology of the area. The geology of the area consists of basement Cape Granite and Malmesbury Group rocks that underlie the sediments of the Sandveld Group. The unconsolidated formations present, are (in order of oldest to youngest) as follows: - Elandsfontyn Formation (oldest): This formation overlies the bedrock in depressions and palaeo-channels in the bedrock. This formation is about 40 m thick and is composed of upward fining quartz sediments. - Varswater Formation: This formation is composed of marine deposits and is restricted to the western (seaward) parts of a bedrock depression to the east of the Langebaan Lagoon and Saldanha. The formation is characterized by rounded quartz grains. - Langebaan Formation: This formation consists of calc-arenites. The sediments are generally grey to cream coloured and consist of quartz and shell fragments, the grain size ranges from coarse to fine and the consolidation is variable. - Witzand Formation (youngest). This formation consists of light-coloured, calcareous, coastal dune sand that can be distinguished from the underlying consolidated Langebaan Formation. The Elandsfontyn Aquifer System (EAS) and the Langebaan Road Aquifer System (LRAS) are the main aquifer systems in the area. These aquifer systems are defined by palaeo-channels that have been filled with gravels of the Elandsfontyn Formation and represent preferred groundwater flow paths. Within each of these aquifer systems (EAS and LRAS) two aquifer units are present. Namely, the confined Lower Aquifer Unit (LAU) geologically consisting of the basal gravels of the Elandsfontyn Formation and the Upper Aquifer Unit (UAU) composed of consolidated sands and calcrete. The two units are separated by a clay aquitard. A numerical model has been established for the area, and extends from the Berg River to the Langebaan Lagoon. Granite outcrop and river system define the other boundaries of the model. Extensive logging of groundwater levels by the Department of Water and Sanitation (DWS) has enabled the accurate establishment of a model. In addition extensive field work and a detailed hydrocensus, as well as the capture of a lot of historical information has resulted in a comprehensive GIS which assists with the refinement of the numerical model. The model provides a valuable tool in modelling potential impacts whether they been from planned groundwater abstraction or artificial recharge. {List only- not presented}

Abstract

The Elandsfontein Phosphate Mine is situated midway between the Langebaan Lagoon and the town of Hopefield. It is located on the Cape West Coast, within the Saldanha Bay Municipality. The mine is positioned within the Elandsfontein Aquifer Unit – which comprises an upper and lower aquifer separated by an aquitard. The economic phosphate layer is situated within the saturated zone of the Upper Aquifer Unit. There are fresh water inflows into the Langebaan Lagoon and all measures must be taken to ensure the natural geohydrological flows are not impacted. Numerous groundwater studies and numerical modelling was carried out to optimize the best way of minimizing the impact on the geohydrology of the area. The dewatering system that has been designed includes re-injection of the groundwater approximately 2 km down-gradient of the open pit. This paper reviews the geological and geohydrological setting of the area and the outcomes of the dewatering and injection systems in place.

Abstract

The Sandveld (Western Cape, South Africa) is a critical potato production area on the national production scale, especially for table potatoes. As the area is situated on the continent’s West Coast, it is a dry area of low rainfall (less than 300 mm /a). The bulk of the irrigation water for agriculture in the region is derived from groundwater. Approximately 60 Mm3 /a of groundwater is abstracted for irrigation of potatoes in the broader Sandveld, assuming a 4-year rotation cycle. The abstraction of groundwater is a sensitive issue in the Sandveld as groundwater also plays a critical role in supplying water to towns in the area, water for domestic use, and it also plays a critical role in sustaining sensitive ecosystems (such as the coastal lake Velorenvlei).

The groundwater resources have been monitored for nearly thirty years now. The results indicate areas where a slow but consistent decline in groundwater levels and groundwater quality is occurring. The trends can also predict when the aquifers will become depleted, and the groundwater will become too saline for use. This is critical information for management interventions to be implemented now to protect the area from irreversible damage.

Abstract

Groundwater is used extensively in the Sandveld for the irrigation of potatoes. The groundwater resources are plentiful and of good enough quality for the production of potatoes, however there has been a significant increase in potato production especially from the period 1975 to 2008. The area planted has increased from 2 369 Ha to 6 715 Ha in this period. The rate of increase has reduced significantly since 2008 and is now quite consistent at approximately 6 800 ha/a. In the region groundwater is vital for the proper functioning of ecosystems and it is also the sole source of water for five towns in the area and supplies most of the domestic water for the farms in the area. Thus the abstraction of groundwater for agriculture needs to be carefully assessed to ensure impacts on other systems and users do not occur.

For this reason Potatoes South Africa has taken the responsible approach of investing in the on-going monitoring of groundwater levels (quantity) and groundwater quality in the Sandveld. PSA appointed the groundwater consultancy, GEOSS to do this monitoring and they have continually committed to this monitoring for the past 10 years. The long term monitoring data has been very valuable in that it shows groundwater trends and the spatial distribution of the measured parameters. Regarding the trends it is clear that certain areas are being over-abstracted and groundwater levels are dropping. In the more critical areas, intervention has occurred - boreholes were closed down and the points of abstraction distributed over a much wider area. This region (Lower Langvlei River) is showing clear signs of recovery both in terms of groundwater levels and quality. The other localized areas where negative trends are evident the land owners have been informed and are aware of the problems. In some critical areas continuous groundwater level loggers have been installed to monitor trends.

The long-term groundwater monitoring, has helped significantly in addressing the negative perception about the widespread impact on groundwater resources due to potato cultivation in the Sandveld. It is important the monitoring continues and regular feedback provided to land owners. The monitoring that the local municipality and the Department of Water Affairs do also needs to be integrated into a single database. It is evident that the initial abstraction of groundwater in the pioneer days of potato cultivation did impact groundwater resources and associated ecosystems in the Sandveld, however currently as the rate of expansion has reduced and stabilized, the groundwater resources closely mimic rainfall patterns and the areas that are being impact are localized, well known and being addressed.

Abstract

VLF-Electromagnetic and geoelectric soundings were carried out at Ibuso-Gboro area via Ibadan, Oyo state. The objective was to delineate the groundwater potentials of the area. VLF-Electromagnetic method was adopted for reconnaissance survey with a view to locating bearing fractured zones in the basement bedrock. Sixteen (16) VLF-Electromagnetic profiles whose length ranges from 90-290 m were occupied with station interval of 10 m. The VLF-Electromagnetic results were presented as profiles. Linear features, suspected to be fractured zones, which were from the anomaly curves of the VLF-Electromagnetic were delineated in seven localities along the profiles. These localities were further confirmed by Vertical Electrical Soundings (VES). The seven Schlumberger Vertical Electrical Soundings (VES) were occupied with the electrode spacing (AB/2) varying from 1 m to 100 m with the total spread length of 200 m. The VES data were presented as sounding curves and interpreted by partial curve matching and computer assisted 1-D forward modeling. The results were presented as geoelectric sections, which showed the subsurface geoelectric images. Two out of the seven delineated linear features were test drilled and the fractured zones were met at depth range of between 25.0 m and 38.2 m beneath borehole (1) and 43.0 m and 52.1 m beneath borehole (2) for confined fractured. The pumping test analysis revealed borehole yield varied from 4.8 m3/hr and 5.2 m3/hr, where three (3) abortive boreholes had earlier been drilled. {List only- not presented} Key Words: VLF-Electromagnetic, Linear features, Geoelectric Soundings and Pumping test.

Abstract

The Smuts House in Centurion is under threat of subsidence due to sinkholes. These sinkholes are linked to the Malmani Dolomite Formation, a Proterozoic carbonate sequence within the Chuniespoort Group of the Transvaal Supergroup, and is subject to sinkhole development (Clay, 1981). In addition to Smuts House, the areas are populated by thousands of people meaning risk of financial damage and, in some cases, loss of property and lives (Trollip, 2006).

The Jan Smuts House Museum is located in a natural park of indigenous trees and shrubs. The area is generally flat-lying; however, various ridges bisect the site in a north-south trend. A koppie (Cornwall Hill) is situated in the north. Outcrops of dolomite and chert characterise most of the study area. The two major streams in the area are that of the Sesmylspruit and Olifantspruit.

This study was undertaken to examine the relationship between subsidence of the Smuts House Museum, subsurface features (geological and anthropogenic) and the local geology. Magnetic and resistivity, active seismic and ground-penetrating radar (GPR) geophysical data were collected, along with x-ray fluorescence (XRF) geochemical data and hydrogeological data.

Abstract

Globally, rivers, lakes and groundwater face complex anthropogenic water quality alterations posing risks to human health, food security and ecosystems. The World Water Quality Alliance (WWQA) forms an open, global consortium, pooling expertise on water quality science and technology innovation and providing a participatory platform for water quality assessments and co-designing tailored and demand-driven services. It addresses priority topics relevant to water governance, scalable water solutions and emerging issues in water management. The African Use Cases provided an initial testbed that puts the quality of surface water and groundwater into the context of the local 2030 Agenda and its multiple linkages across the Sustainable Development Goals. Central to the initial Africa Use Cases was the integration of in-situ, remote sensing-based earth observation and modelling data to derive the best possible current state of water quality (baseline). Of the three African Use Cases, “Cape Town’s Major Aquifer Systems” focused mainly on groundwater quality in an urban environment. One of the success factors for the Cape Town Aquifer Use Case was the ability of the team to integrate the three different data types of the triangle approach on a sub-catchment scale. This required understanding the complex surface and groundwater systems and their interaction (flow paths and fluxes) in the urban environment. A robust stakeholder engagement process and the introduction of transformative art also drove the success of the Cape Town Use Case. The outcomes of this process will be presented and discussed in this presentation.

Abstract

Test-pumping drawdown curves do not always sufficiently indicate aquifer characteristics and geometry and should never be analysed in isolation. Using derivative analysis and flow dimension theory, inferring the regional geometries and flow characteristics of fractured aquifers that are otherwise unknown or inconclusive is possible. As the drawdown and/or pressure front propagates through the aquifer, it reaches various hydrogeological objects that influence flow regimes and imprints a sequence of signatures in the drawdown derivative curve. The conjunctive interpretation of these flow regime sequences and hydrogeological data results in a robust, well-informed conceptual model (in terms of both local groundwater flow and the aquifer), which is vital for sustainable groundwater resource management. Derivative and flow regime analysis was applied to the test-pumping data of confined and unconfined Nardouw Aquifer (Table Mountain Group) boreholes within Steenbras Wellfield (Western Cape). Major NE-SW trending folding and transtensional Steenbras-Brandvlei Megafault Zone, in association with cross-cutting faults/fractures and younger False Bay Suite dykes, make the Nardouw Aquifer (and deeper Peninsula Aquifer) hydrogeologically complex. The sequential flow regime analyses reveal domains of conceptual flow models, including open vertical fractures, T-shaped channels, double (triple) porosity models, and leaky/recharge boundary models, amongst others. Appropriate analytical flow models (type curve fitting) are then applied for accurate aquifer parameter estimations, which are used to evaluate recommended long-term yields through predictive pumping scenarios. The outcome is an improved hydrogeological understanding and enhanced conceptual model of the aquifer, which informs numerical modelling, ecological protection, and groundwater resource management.

Abstract

The freshwater resources of the world are under pressure to meet the growing demands of rapidly increasing populations and their various activities. South Africa receives less than the world’s average annual rainfall and this suggests that it is a potential candidate for water stress. Rising demand for increasingly scarce water resources is leading to growing concerns about future access to water, particularly in urban areas.

Groundwater is generally not utilised as a significant source of water supply in urban areas. Currently, groundwater makes up only small portion (up to 6%) of the supply in those metropolitan municipalities that use it. Water supply generally comes from local resources as urban areas establish, and is replaced by imported water as cities grow. Further to groundwater not being widely used for supply in urban areas, it is generally being mis-used or at least indirectly used with negative consequences. Urban areas have surfaces that are sealed preventing infiltration and recharge, generating massive surface runoff and stormwater which is discharged downstream of the urban area. Leakage of the reticulation and sewer network causes an increase in recharge. The associated contamination and water quality impacts may render the groundwater resources in the urban areas not fit for supply. The sustainability challenge for urban water management is to remediate or at least isolate poor water quality, whilst making use of the local resources.

To overcome these challenges, and specifically to address the contradictory nature of urban (ground) water resources, the role of groundwater in town planning (Spatial Development Frameworks), in development planning (Integrated Development Plans), and in Water Sensitive Design (WSD) must be strengthened. This paper summarises preliminary findings from a Water Research Commission project aimed at to improving urban groundwater management practices and developing a research strategy for developing and managing urban groundwater resources. The current state-of- the-art for urban groundwater resources use and management are assessed leading to the preliminary identification of gaps.

Abstract

In  South  Africa  salinisation  of  water  resources  by  dissolved  sulphates  resulting  from  acid  rock drainage (ARD) and metal leaching (ML) from surface coal mine spoils has a significant effect on water supply in the Gauteng Province. Predictions of mine water quality is required to select cost- effective rehabilitation and remediation measures to reduce future ARD and ML risks and to limit long-term  impacts.  A  load  balance  model  was  developed  in  Microsoft  Excel  to  simulated contaminant loads in a completely backfilled opencast mine in the Karoo Basin of South Africa after closure. The model calculated the balance between contaminant load into the pit water system from mainly pyrite oxidation processes in the spoils and load removed through decanting. Groundwater flow modelling data and simulated spoils seepage qualities for the mine site were used as input in the contaminant load calculations. The model predicted that the amount of contaminants added to the pit from spoils decrease considerably from the time of closure over a period of approximately 100 years. Thereafter the contaminant load decrease is gradual. This is due to a decrease in the volume of unsaturated spoils, as spoils at the bottom become permanently inundated as the pit fills up, thus limiting oxygen diffusion and oxidation. Cumulatively, the contaminant load gradually increases  in  the  backfilled  pit  until  the  onset  of  subsurface  and  surface  decant,  when  the contaminant load declines. This is due to removal of contaminants from the mine water system via decanting. Approximately 200 years after mine closure, 86% of the spoils are inundated. The model predicted that the quality of decanting water improves with time due to a decrease in load from spoils, removal of contaminants through decanting water and dilution effects of relatively clean groundwater inflows. Mass loads were used as input into the numerical groundwater model for the contaminant mass transport simulations to predict the migration of contaminant plumes with time. The geochemical model results assisted in developing conceptual water and waste management strategies for the opencast mine during operational and closure phase.

Abstract

Case studies illustrate a conceptual framework for shallow groundwater flow systems’ temporal and spatial variability with groundwater-surface water interactions in the Boreal Plains of Canada. The framework was developed using a twenty-year hydrometric dataset (e.g., climatological and streamflow data, hydraulic heads, vertical hydraulic head gradients, geochemical and isotopic signatures). The region is characterized by low-relief glacial landscapes, with a mosaic of forestlands and peatlands, and a subhumid climate, resulting in spatially heterogeneous storage and transmission properties, variable recharge and evapotranspiration potentials, and highly complex patterns of water movement. Two primary spatiotemporal scales were examined to create a holistic, variable-scale conceptual model of groundwater movement: the large scale (e.g., glacial landforms, regional topography, decadal climate cycles) and the small scale (e.g., individual landcover, local hummocks, annual moisture deficits). Water table behaviour, evapotranspiration rates, and runoff were controlled by a hierarchy of interactions between hydrological processes occurring at different spatiotemporal scales; however, the specific order of controls depends on the hydrogeological setting. The case studies, supported by empirical and numerical modelling, demonstrate that smaller-scale heterogeneities in geology and recharge can dominate over topographic controls, particularly in areas with high conductivity or hummocky terrain, where the climate, geology, and topographic relief are similar. Many hydrogeological studies rely on surface topography as a first‐order control; however, with field observations and modelling, this conceptual framework demonstrates the need to consider the potential dominance of subsurface characteristics and processes, plus climate, especially in landscapes with low recharge and low relief.

Abstract

Groundwater is the most important source of potable water in rural areas of Acholiland, a sub-region of northern Uganda. Installation of handpumps has been the focus of local government and international aid to provide safe drinking water in Uganda. However, non-functional handpumps are one reason for the abandonment of groundwater resources. For handpumps to be sustainable for years, appropriate siting and construction is required, as well as monitoring. This is common knowledge to specialists working in rural supply, but gaps in knowledge transfer and field skills may exist for the persons installing and maintaining handpump wells. This is a case study of a ten-day field campaign designed to train local participants who actively work in the rural groundwater supply sector. Nine non-functional handpump sites were identified for repair and hydrogeology and geophysical studies. A non-governmental organization, IsraAID, along with Gulu University implemented training by hydrogeology specialists to build local capacity. The training included handpump functionality tests, downhole inspections, electrical resistivity tomography surveys, and water quality sampling, including a novel Escherichia coli test that did not require an incubator. Functionality tests and downhole inspections provided simple but effective ways to assess handpump and well issues. Training in water quality empowered the participants to complete rapid assessments of the quality of the water and start monitoring programs. The success of the project was based on collaboration with multiple organizations focusing on the development of local capacity. The lessons learnt from this campaign should be considered for other rural groundwater supply scenarios.

Abstract

In order to meet the increasing national and international demand for coal, substantial expansion plans for existing as well as new coal mines were put forward in recent years. The mine developments are often proposed in environmentally sensitive areas and require an appropriate assessment of potential environmental impacts, including impacts on groundwater dependent ecosystems. This paper describes the development of a conceptual and numerical groundwater model as part of a wetland reserve determination in the Witbank coalfields. The model was used to assess potential mining related impacts on the shallow groundwater flow, including surface seepages and spring discharges feeding hill slope and valley bottom wetlands as well as pans. A number of shallow monitoring boreholes were sited, drilled and tested in the focus area around a pan to characterise the shallow perched and weathered aquifers. While these aquifers were generally found to be very low to low yielding, higher yields were encountered in a coarser grit layer intersected by two of the eight boreholes. The grit layer represents a potential preferential groundwater flow path towards the pan and was subsequently further delineated based on the exploration drilling logs from the mine. The different aquifers, the target coal seam, and over 60 mapped hill slope and valley bottom wetlands as well as pans, were incorporated into a numerical groundwater flow model. A free seepage boundary was assigned to the entire surface area to evaluate if the model is able to represent the observed seepages and spring discharges. The simulation of unsaturated flow processes (Richard's equation) was found to be crucial for the representation of discharges from perched aquifers. Following a satisfactory calibration of the model, different open cast mine layouts were then incorporated into the model to assess their impacts on the groundwater contribution to wetlands. The presented quantitative simulation of groundwater contributions towards wetlands and pans based on site specific groundwater investigations and data is considered a best practice example in assessing the groundwater component for a wetland reserve determination.

Abstract

Many of South Africa’s coal fields are characterised by a complex lateral and vertical pattern of mine voids, targeting different lease areas and coal seams, and applying different mining methods such as open cast (strip) and underground (board and pillar) mining. Many are at different stages in their life of mine from exploration to closure stage.

Despite the general recognition that the water management or absence thereof at neighbouring mines influences each other (evident for example in the recognition of inter-mine flow in the overall water balance for a site), and the requirement of cumulative impact assessments, very few studies actually attempt to tackle and quantify cumulative impacts of numerous mines on the ambient groundwater environment. While the parameterisation and calibration of a groundwater model for a single mine is often hampered by environmental data scarcity, the absence of cumulative impact assessments is mostly related to the unwillingness of neighbouring and competing mines to share these data. Soft- and hardware as well as budget limitations pose additional challenges for the development of regional groundwater models taking cognisance of complex mining environments.

This paper describes a regional groundwater flow model that takes into account five surface and underground mining areas. The different start and closure dates for the opencast and underground mining areas result in a complex mining schedule, with groundwater abstractions and inflows for the different areas potentially influencing each other during life of mine and post-closure and requiring therefore a simultaneous simulation thereof.

A further complication in the model development was the explicit consideration of cut-and-fill operations, necessitating alterations of the model topography to reflect annual cuts as free seepage boundaries, and to reflect rehabilitated backfilled areas with topography different from the pre-mining environment. The case study has led to numerical model software developments to enable transient changes in layer elevations over a simulation period.

While the model attempted to simulate the cumulative impact of the mines, it was also used to predict the impact of a new mining development on the life of mine and post-closure water balances for the remainder of the neighbouring mines. The model outcomes could therefore theoretically inform apportionment of post-closure liabilities.

Abstract

The assessment and prediction of mine water rebound has become increasingly important for the gold mining industry in the Witwatersrand basin, South Africa. The cessation of dewatering lead to large volumes of contaminated surface discharges in the western parts of the basin. Towards the eastern extremity of the Witwatersrand basin the detached Evander Goldfield basin has been mined since the early 1950s at depths between 400 and 2 000 m below ground, while overlain by shallower coal mining operations. The hydrogeology of the Evander basin can be categorised by a shallow weathered-fractured rock aquifer comprising of the glacial and deltaic sediments of the Karoo Supergroup, while the deeper historically confined fractured bedrock aquifer consist predominantly of quartzite with subordinate lava, shale and conglomerate of the Witwatersrand Supergroup. The deep Witwatersrand aquifer has been actively dewatered for the last 60 years, with a peak rate of 60 Ml per day in the mid late 1960s. Modelling the impacts of mine dewatering and flooding on a regional scale as for the Evander basin, entails challenges like the appropriate discretisation of mine voids  and  the  accurate  modelling  of  layered  aquifer  systems  with  different  free  groundwater surfaces on a regional scale. To predict the environmental impacts of both the historic and future deep mining operations at Shaft 6, the detailed conceptual model of the aquifer systems and three- dimensional model of the mine voids were incorporated into a numerical groundwater model to simulate the dewatering and post-closure rebound of the water tables for the basin. The presented model could serve as an example for the successful modelling of mine dewatering and flooding scenarios for other parts of the Witwatersrand basin.

Abstract

The assessment and prediction of mine water rebound has become increasingly important for the gold mining industry in the Witwatersrand basin, South Africa. The cessation of dewatering lead to large volumes of contaminated surface discharges in the western parts of the basin. Towards the eastern extremity of the Witwatersrand basin the detached Evander Goldfield basin has been mined since the early 1950s at depths between 400 and 2000 metres below ground, while overlain by shallower coal mining operations. The hydrogeology of the Evander basin can be categorised by a shallow weathered-fractured rock aquifer comprising of the glacial and deltaic sediments of the Karoo Supergroup, while the deeper historically confined fractured bedrock aquifer consist predominantly of quartzite with subordinate lava, shale and conglomerate of the Witwatersrand Supergroup. The deep Witwatersrand aquifer has been actively been dewatered for the last 60 years with a peak rate of 60 Ml per day in the mid late 1960s. Modelling the impacts of mine dewatering and flooding on a regional scale as for the Evander basin entails challenges like the appropriate discretisation of mine voids and the accurate modelling of layered aquifer systems with different free groundwater surfaces on a regional scale. To predict the environmental impacts of both the historic and future deep mining operations, the detailed conceptual model of the aquifers systems and a 3-dimensional model of the mine voids were incorporated into a numerical groundwater model to simulate the dewatering and post-closure rebound of the water tables for the basin. The presented model could serve as an example for the successful modelling of mine dewatering and flooding scenarios for other parts of the Witwatersrand basin.

Abstract

Millions of tons of coal ash are produced across the globe, during coal combustion for power generation. South Africa relies largely on coal for electricity generation. The current disposal methods of coal ash are not sustainable, due to landfill space limitations and operational costs. One way/means of disposing of coal ash that could provide environmental and financial benefits; is to backfill opencast mines with the ash. However, a limited number of studies have been conducted to assess the feasibility of this method in South Africa. Thus the aim of the experiment is to monitor bulk ash disposal under field conditions to improve the understanding of the geochemical and hydrogeological processes occurring during the actual deposition of coal ash in opencast coal mines. To achieve the aim (1) a gravity lysimeter will be built containing both mine spoils and coal ash representing field conditions; (2) the factors (CO2, water level and moisture content) affecting acid mine drainage will be monitored in the lysimeter and (3) the change in the quantity and quality of the discharge released from the lysimeter.

Abstract

Groundwater provides an important buffer to climate variability in Africa. Yet, groundwater irrigation contributes only a relatively small share of cultivated land, approximately 1% (about 2 mill. ha) as compared to 14% in Asia. While groundwater is over-exploited for irrigation in many parts in Asia, previous assessments indicate an underutilized potential in parts of Africa. As opposed to previous country-based estimates, this paper derives a continent-wide, distributed (0.5 degrees spatial resolution) map of groundwater irrigation potential, indicated in terms of fractions of cropland potentially irrigable with renewable groundwater. The method builds on an annual groundwater balance approach using 41 years of hydrological data, allocating only that fraction of groundwater recharge that is in excess after satisfying other present human needs and environmental requirements, while disregarding socio-economic and physical constraints in access to the resource. Due to high uncertainty of groundwater environmental needs, three scenarios, leaving 30, 50 and 70% of recharge for the environment, were implemented. Current dominating crops and cropping rotations and associated irrigation requirements in a zonal approach were applied in order to convert recharge excess to potential irrigated cropland. Results show an inhomogeneously distributed groundwater irrigation potential across the continent, even within individual countries, mainly reflecting recharge patterns and presence or absence of cultivated cropland. Results further show that average annual renewable groundwater availability for irrigation ranges from 692 to 1644 km3 depending on scenario. The total area of cropland irrigable with renewable groundwater ranges from 44.6 to 105.3 mill. ha, corresponding to 20.5 to 48.6% of the cropland over the continent. In particular, significant potential exists in the semiarid Sahel and eastern African regions which could support poverty alleviation if developed sustainably and equitably. The map is a first assessment that needs to be complimented with assessment of other factors, e.g. hydrogeological conditions, groundwater accessibility, soils, and socio-economic factors as well as more local assessments.

Abstract

Identifying and characterising the vertical and horizontal extent of chlorinated volatile organic compound (CVOC) plumes can be a complex undertaking and subject to a high degree of uncertainty as dense non-aqueous phase liquid (DNAPL) movement in the subsurface is governed most notably by geologic heterogeneities. These heterogeneities influence hydraulic conductivity allowing for preferential flow in areas of higher conductivity and potential pooling or accumulation in areas of lower conductivity. This coupled with the density-induced sinking behaviour of DNAPL itself and the effects of groundwater recharge in the aquifer result in significant challenges in assessing the distribution and extent of CVOC plumes in the subsurface. It has been recognized that high resolution site characterization (HRSC) can provide the necessary level of information to allow for appropriate solutions to be implemented to mitigate the effects of subsurface contamination. Although the initial cost of HRSC is higher, the long-term costs can be substantially reduced and the remedial benefits far greater by obtaining a better understanding of the plume characteristics upfront. The authors will discuss a case study site in South Africa, where ERM has conducted HRSC of a CVOC plume to characterise the distribution of the source area and plume architecture in order to assess the potential risk to receptors on and off-site. The source of impact resulted from the use of a tetrachloroethene (PCE)-based solvent in an on-site workshop. The following methods of characterization were employed:
- Conducting a passive soil gas survey to identify and characterise potential source zones and groundwater impacts;
- Vertical characterisation of the hydrostratigraphy, contaminant distribution and speciation in real time using a Waterloo Advanced Profiling System (APS) with a mobile on-site laboratory;
- Using the Waterloo APS data to design and install groundwater monitoring wells to delineate the vertical and lateral extent of contamination; and
- Conducting a vapour intrusion investigation including sub-slab soil gas, indoor and outdoor air sampling to estimate current risk to on-site employees.
In less than a year, the risk at the site is now largely understood and the strategies for mitigating the effects of the contamination can be targeted and optimised based on the information gained during the HRSC assessment.

Abstract

Many aquifer systems worldwide are subject to hydrochemical and biogeochemical reactions involving iron, which limit the sustainability of groundwater schemes. This mainly manifests itself in clogging of the screen and immediate aquifer with iron oxyhydroxides resulting in loss of production capacity. Clogging is caused by chemical precipitation and biofouling processes which also manifests in South African well-fields such as in Atlantis and the Klein Karoo. Both well-fields have the potential to provide a sufficient, good quality water supply to rural communities; however, clogging of the production boreholes has threatened the sustainability of the schemes as quality and quantity of water is affected. Rehabilitation of the affected boreholes using techniques such as the Blended Chemical Heat Treatment method does not provide a long-term solution. Such treatments are costly with varying restoration of original yields achieved and clogging recurs with time. Currently the research,  management  and  treatment  options  in  South  Africa  have  focused  on  the  clogging processes which are complex and site-specific, making it extremely difficult to treat and rectify. This project attempts to eliminate elevated concentrations of dissolved iron, the cause of the clogging. High iron concentrations in groundwater are associated with reducing conditions in the aquifer allowing for the dissolution of iron from the aquifer matrix. These conditions can be natural or human-induced. Attempts to circumvent iron clogging of boreholes have focussed on increasing the redox potential in the aquifer, by injection of oxygen-rich water into the system, to prevent dissolution and to facilitate fixation of iron in the aquifer matrix. Various in situ treatment systems have  been  implemented  successfully  overseas  for  some  time.  In  South  Africa  thus  far  in  situ treatment of iron has only been proposed as a solution for production borehole clogging. Based on experience from abroad the most viable option to research the elimination of ferrous iron in South African aquifer systems would be through the in situ iron removal treatment. Different techniques of increasing the dissolved oxygen concentration in the injected water to intensifying the redox change in the aquifer can be applied; however, the use of ozone as the oxidant is a new approach. Its effectiveness is evaluated by the results in iron removal in surface water treatment for drinking water supply.

Abstract

Worldwide many aquifer systems are subject to hydrochemical and biogeochemical reactions involving iron which limit the sustainability of groundwater schemes. This mainly manifests itself in clogging of the screen and immediate aquifer with iron oxyhydroxides resulting in loss of production capacity of the borehole. Clogging is caused by chemical precipitation and biofouling processes which also manifests in South African wellfields such as the Atlantis and the Klein Karoo Rural Water Supply Scheme. Both wellfields have the potential to provide a sufficient, good quality water supply to rural communities, however clogging of the production boreholes has threatened the sustainability of the scheme as quality and quantity of water is affected. Repeated rehabilitation of the affected boreholes using techniques such as the Blended Chemical Heat Treatment (BCHT) method does not provide a long term solution. Such treatments are costly with varying restoration of original yields achieved and clogging recurs with time. Currently, the research, management and treatment options in South Africa have focused on the clogging processes which are complex and site specific making it extremely difficult to treat and rectify. This project attempts to eliminate the cause of the clogging which is elevated concentrations of dissolved iron. High iron concentrations in groundwater are associated with reducing conditions in the aquifer allowing for dissolution of iron from the aquifer matrix. These conditions can be natural- and/or human-induced. Attempts to circumvent iron clogging of boreholes have focussed on increasing the redox potential in the aquifer to prevent dissolution and facilitate fixation of the iron in the aquifer matrix. Various in situ treatment systems have been implemented successfully overseas for some time. However, in South African in situ treatment of iron has only been a theoretical approach. Based on experience from abroad the most viable option to research and apply elimination of ferrous iron in South African aquifer systems would be through the in situ iron removal treatment The objective of this paper is to set out the experience from abroad and to outline the initial results of this treatment. A pilot plant for testing the local applicability of this method was constructed at the Witzand wellfield of the Atlantis primary aquifer on the West coast of South Africa.

Abstract

The development of groundwater supply schemes is on the increase in South Africa. However, the sustainability of many of these wellfields is threatened due to the presence of iron (Fe2+) and manganese (Mn2+) ions in the groundwater. Their occurrence can manifest in problems with water quality and supply to consumers. The World Health Organisation recommends the removal of iron and manganese to below 0.3 mg/? and 0.1 mg/? respectively, to circumvent water quality risks. However, production borehole clogging is of greatest concern in the operation of wellfields due to the severe cost implications associated with reduced production. Clogging is caused by the precipitation of iron- and manganese-oxides at the borehole screen initiated by biogeochemical processes. Since Fe2+ and Mn2+ ions and the bacterial populations are naturally present in anoxic/anaerobic aquifer systems and the ingress of oxygen through pumping cannot be entirely prevented. The only approach to controlling borehole clogging is through management and rehabilitation procedures. Locally, these procedures have been implemented and in severe clogging cases the Blended Chemical Heat Treatment method has been applied. However, the effectiveness of rehabilitation has been limited. This can be ascribed to factors such as the incorrect production borehole design

Abstract

Identifying groundwater recharge and discharge areas across catchments is critical for implementing effective strategies for salinity mitigation, surface water and groundwater resource management, and ecosystem protection. This study seeks to identify potential GW-SW discharge and recharge areas around the Barotse Floodplain. The results of remote sensing analysis using the Normalised Difference Vegetation Index (NDVI) show that the vegetation is sensitive to the dynamics of groundwater level, with shallower levels (< 10 m) in the lower reaches compared to deeper levels (>10 m) in the upper catchment). These zones are further investigated and likely represent geological variability, aquifer confinement and the degree of GW-SW interactions. GW-SW interactions likely are influenced by an interplay of factors such as water levels in the groundwater and surface level and hydrogeological conditions. Based on the findings, the wetland hosts riparian vegetation species responsive to the groundwater dynamic. NDVI can thus be used as a proxy to infer groundwater in the catchment. Therefore, effective water resources management of the floodplain should be implemented through conjunctive management of groundwater and surface water.

Abstract

Coal Ash Beneficiation is a government imperative for South Africa, and Eskom generates approximately 34 million tons of coal ash annually from their 14 pulverised coal fuel plants. It is estimated that there are approximately 6,000 abandoned coal mines in South Africa, of which 2,322 are classified as high risk, contributing to subsidence and the generation of acidic mine drainage. It is envisaged that coal ash could offer a support medium for the mines and neutralise the acidic mine water due to its alkaline nature. The Department of Fisheries, Forestry and the Environment has supported the initiative but has requested a means of modelling possible contamination due to placing the coal ash in these environments. To this end, laboratory trials were completed to generate the initial model and a controlled pilot site was established to validate the model’s accuracy. This trial evaluated stabilised and unstabilised coal ash as a means of acid water management. The laboratory trials showed that the ash could neutralise the pH of the mine water from approximately 2 to 7; this was sustained for the test period. In addition, sulphate and iron were significantly reduced in the treated water. The laboratory and site work results will be detailed in this presentation.

Abstract

As populations, agricultural and industrial demands grow with time, increasing attention is placed on developing groundwater resources in a sustainable manner. At the small, local scale, this tends to involve exploration (scientific and otherwise) and test pumping (also subject to more and less scientific methods). While there can be some subjectivity in the analysis of scientific test pumping data (the selection of representative periods of drawdown stability, the inclusion of potential boundary conditions and the estimation of available drawdown), published methodologies such as the FC method (2001) and the Q20 (1959) and R20 (2006) concepts attempt to calculate sustainable abstraction rates based on these tests. At a larger catchment or aquifer scale, water balance estimates of inflows, storage and outflows are also used to estimate the effects of groundwater abstraction within such a “water budget”. This can be done conceptually, but is often also through a numerical model. A drawback of such methods is the difficulty in estimating representative annual inflow volumes, such as groundwater recharge. One such methodology is the Aquifer Firm Yield Model (2012) which assesses sustainable groundwater supplies based on threshold recharge inflows, baseflow and evapotranspiration outflows, and a 5 m aquifer saturated fluctuation limit. While this was intended for use at a preliminary stage of investigations, before sufficient hydrogeological data would be available for a numerical model, it nonetheless provides an estimate of the available groundwater for abstraction based on a water budget concept rather than test pumping data analysis. A comparison of the results of these two approaches is provided for several newly developed municipal production boreholes in the Karoo to compare where the assumptions inherent to each approach may be highlighted by noticeable differences in results.

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

Estimating pumping rates for the purpose of equipping boreholes with suitable pumps that will not over abstract either the boreholes or the aquifer(s) that are intersected is often assessed through test pumping of the boreholes prior to pump selection. While the South African National Standard has guidelines on the methodologies and durations of these tests (SANS 10299-4:2003), many production boreholes in the agricultural and industrial sectors are still equipped based upon so called Farmer Tests or Pump Inlet Tests (PIT), often of a short (6-24 hour) duration. These tests are also frequently and incorrectly confused with a Constant Head Test (CHT), both of which are different in methodology to SANS 10299-4:2003 testing, which relies to a high degree on data collected during a Constant Discharge/Rate Test (CDT or CRT) and recovery thereafter. The study will assess differences in test pumping methodology, data collection, analysis methodology and final recommendations made between Farmer Tests and SANS 10299-4:2003 methodology tests for 20 boreholes in which both tests were performed. The selected sites cover a variety of geological and hydrogeological settings in the Western Cape. Test comparisons include boreholes drilled into the Malmesbury Group, Table Mountain Group and Quaternary alluvial deposits, with tested yields ranging from 0.5 – 25 L/s.

Abstract

Test-pumping drawdown curves are not always sufficiently indicative of aquifer characteristics and geometry. In fact, drawdown curves should never be analysed and interpreted alone. The derivative analysis (Bourdet et al., 1983) and flow dimension theory (Barker, 1988) make it possible to infer the regional geometries and flow characteristics of fractured aquifers which are otherwise often unknown or inconclusive when interpreting point-source borehole logs. The propagation of the drawdown and/or pressure front through the aquifer reaches distal hydrogeological objects which influence the flow regime and imprints signatures in the drawdown derivative curves. The conjunctive interpretation of these flow regime sequences and geological data results in a robust, well-informed conceptual model which is vital for resource management.

A methodology similar to that of A. Ferroud, S. Rafini and R. Chesnaux (2018) was applied to the test-pumping data of 14 confined and unconfined Nardouw Aquifer boreholes in the Steenbras area, Cape Town, which has been under exploratory investigation since the early 2000’s. The Steenbras wellfield was developed following the major 2017-2018 Western Cape drought. The NE-SW trending open folds and dextral strike-slip Steenbras-Brandvlei Megafault Zone (with crosscutting faults and dykes) make the aquifer hydrogeologically complex. It is due to these complexities that the sequential flow regime analysis was undertaken to enhance the current conceptual understanding.

The analyses reveal domains of flow models which include open vertical fracture, T-shaped channel, double(triple) porosity model, and leaky/recharge boundary amongst others. Poor data quality and noise issues are also highlighted. The outcomes of the sequential flow regime analysis allow for identification of applicable flow models for type curve fitting to avoid erroneous aquifer parameter estimations; improvement of the hydrogeological understanding of the aquifer; enhancements of the current conceptual model in order to inform on subsequent numerical modelling, groundwater resource management and ecological protection.

Abstract

Across Africa, given the pressing challenges of climate change and widespread water, food and livelihood insecurity and poverty, there is an ever-increasing expanding role for groundwater in resilience building, especially in borderland communities. This situation is being investigated in several projects and geographies. This paper’s groundwater management analysis was based on literature reviews, key informant interviews (KIIs), and focus group discussions (FGDs) in selected case study areas throughout sub-Saharan Africa. The KIIs included representatives of water management institutions, community leaders, international development partners, the private sector and non-governmental organisations (NGOs) involved in the use or management of groundwater. The FGDs occurred in borderland communities in Ethiopia, Kenya, and Somalia (with these three countries sharing borders) and Mozambique, South Africa and Zimbabwe (with these three also sharing borders). The findings show that informal institutions such as clan, tribal or ethnic affiliations dictate access to natural resources such as groundwater in borderlands. These same Institutions also play a significant role in conflict resolution in the borderland areas. In addition, informal institutions play an essential role in groundwater management and should also be recognised – in engagements and formal water policies and legislation. Formal organisations, institutions and government structures should strengthen their focus on ensuring that discussions and decisions include informal role players. Further developing and enforcing conventions, land-use plans, and bylaws governing access to and use of groundwater should ensure engagement and co-creation of solutions towards effective water resource management.

Abstract

The groundwater governance arrangements for the development of groundwater resources were analysed. The analysis highlighted gaps and barriers to overcome before unconventional gas (shale gas and coal bed methane) development can take place at an industrial scale. The following governance challenges were identified (i) setting baseline measurements to detect groundwater pollution and to determine resource status; (ii) review of licenses and setting conditions for the development of unconventional resources; (iii) compliance monitoring and enforcement systems in place (iv) dealing punitively with non-compliant operators (v) mitigation options in place to prevent groundwater pollution; (vi) goal-based regulatory framework in place rather than a prescriptive regulatory framework; (vii) disclosure of hydraulic injection fluid; (viii) coordination with other government departments and regulatory bodies; (ix) a framework for subsidiarity and support to local water management; and (x) an incentive framework that support good groundwater management. To overcome the challenges requires a decentralized, polycentric, bottom-up approach, involving multiple institutions to deal with unconventional gas development. This provides better conditions both for cooperation to thrive and for ensuring the maintenance of such institutions.

Abstract

The EKK-TBA is significant in anchoring Gross Domestic Product growth and development in both countries is heavily reliant on groundwater. Recently a transboundary diagnostic analysis (TDA) and a strategic action plan (SAP) for the EKK-TBA was completed. The analysis resulted in a three-fold expansion of the EKK-TBA boundary. The new EKK-TBA boundary overlaps part of the Okavango and Zambezi River Basins and now also includes major wellfields in Botswana and Zimbabwe (Nyamandlovu and Epping Forest) as well as the Makgadikgadi Pans which act as the surface water and groundwater discharge zone.

An analysis of institutional arrangements was carried out to enhance effective and efficient management of the EKK-TBA. Noting the complexity of the EKK-TBA. the initial institutional response could potentially be the development of a bilateral agreement between Botswana and Zimbabwe for cooperation and coordination to support the management of the TBA. This agreement would seek to establish a Joint Permanent Technical Committee (JPTC) that would also co-opt in members from the two shared watercourse commissions. Such a JPTC would enable improved coordination across the varying transboundary dimensions and would align with the precepts of the Revised Protocol on Shared Watercourses. This would include such principles including sustainable utilization, equitable and reasonable utilisation and participation, prevention, and co-operation, as well as aspects of data and information exchange and prior notification.

Abstract

Water security is pivotal for economic growth, sustainable development and poverty reduction in SADC. Increasing aridity and dwindling surface water supplies are resulting in new opportunities for groundwater as a source for domestic, agricultural and industrial use. We carried out an assessment of groundwater governance in the SADC region to determine the effectiveness of provisions to regulate groundwater. Numerous sources of information were solicited, reviewed, and data was mined using framework analysis and qualitative context analysis approaches. This provided a systematic model for managing and mapping the data. There is a good understanding of aquifer systems at the regional level. Transboundary aquifers have been delineated and areas prone to groundwater drought have been identified. Information systems to manage groundwater data, however, are disparate throughout the region and institutions to manage groundwater are inadequate and are functioning within an environment of scarce financial and human resources. The hydrogeological capacity in public institutions such as government departments is a major concern and regulations to protect groundwater resources are often not in place. This includes instruments to control groundwater abstraction and potentially polluting activities. Where regulatory instruments are in place, often no enforcement or sanctions of unlawful activities are taking place. There is also limited coordination with other sectors such as energy and mining. Furthermore, the implementation of groundwater management action plans, where developed, is weak. Overall, groundwater management in the SADC region was found to be poor. Whilst the groundwater governance challenges are great, there are opportunities to support diagnostic analysis of transboundary aquifer systems, competency development, establishing regional groundwater monitoring networks, strengthening institutional frameworks, and development of groundwater resources, e.g. to clear the backlog in access to improved water supply.

Abstract

The Department of Water and Sanitation reviewed and re-designed (optimised) the national water resources monitoring networks. During the re-design, monitoring objectives were formulated and prioritised. The highest priority, i.e. to make available data and information related to quantity and quality of present and future water resources is through planned infrastructure development and other interventions. The data and information dissemination aims at providing strategic decision support for the equitable and sustainable allocation of resources to the population, environment and other economic sectors of society. In setting up the groundwater monitoring network, an approach was followed which allowed for the incorporation of local and international best-practice; hydrogeological information combined with expert knowledge. We used the following criteria to establish the baseline or background sites for the national groundwater monitoring network: borehole spatial densities; pristine areas (no land-use activities); aquifer yield; recharge; baseflow; sites for background monitoring related to groundwater reserve determinations and the setting of resource quality objectives; springs; and international obligations. Trend monitoring sites were selected around baseline sites and around towns who were groundwater dependent. The trend monitoring sites allow for trends to be determined in terms of: (i) over-exploitation/abstraction of groundwater; (ii) groundwater quality degradation from various land use practices; and (iii) groundwater water use. Regional Spatial Design Workshops were held to compare the existing water resources monitoring network with the newly designed network and the existing monitoring network were optimised accordingly. Google Earth was used to query the detail of the monitoring sites, consider land-use coverages and incorporated expert input to position sampling points in line with the monitoring objectives. The implementation of the updated groundwater monitoring network will rely predominantly on hydrogeological considerations and field-
based investigations and observations. When the networks are optimised, statistical techniques will be useful to ascertain monitoring point location, redundancy and frequency.

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

South Africa has an energy crisis. The country requires 53 Gigawatt of new capacity by 2030. The exploitation  of  unconventional  gas  is  a  potential  game-changer  to  meet  South  Africa’s  current energy deficit to fuel economic growth and development. Water management, both in terms of abstraction and disposal, has emerged as a critical issue in the development of unconventional gas reservoirs. This presentation focuses on a high-level, qualitative analysis of the groundwater-related institutional and governance challenges associated with unconventional gas exploration and production. The findings represent a synthesis of information sourced from regulatory and legislative documents as well as international experience. The analysis maps the current groundwater institutional and governance landscape in South Africa and lessons learned from other regimes such as the United Kingdom and United States of America. Good governance entails ensuring that there is compliance with policy and legislation, effective decision-making, appropriately allocated accountability, transparency and that stakeholder interests are considered and balanced. This forms the basis of a preliminary gap analysis.

Abstract

The Elandsfontein aquifer is currently under investigation to assist with the management of the system and to ensure the protection of the associated Langebaan lagoon RAMSAR site. The Elandfontein aquifer unit is situated adjacent to the Langebaan Road aquifer in the Lower Berg River Region and is bounded by the Langebaan Lagoon, possible boundary towards Langebaan Road aquifer, the Groen River bedrock high and the Darling batholith. The study will investigate the boundaries and hydraulic characteristics of the different aquifers and aquitards (Elandsfontein clay layer) in the Elandsfontein unit and their relationship to the Langebaan Lagoon. A literature review and baseline study has been completed to determine groundwater flow patterns and the general distribution of water quality, using historic data to characterize the different aquifers and aquitards of the system. An initial conceptual model has been formulated based on this data. Pumping tests will be used to acquire hydraulic characteristics of the Elandsfontein aquifer where data gaps exist, together with water quality and stable isotope sampling. Future plans are to construct a groundwater numerical flow model of the Elandsfontein system to assist with the management of the complex relationships between the recharge areas, flow paths through the different aquifer layers and aquitards towards the Langebaan Lagoon discharge. Results will be presented using graphical methods such as time series graphs amongst the monitoring boreholes over the years, piper diagrams to show water type characterization (Na-Cl type water) and initial results from the groundwater flow model. The expected results are envisaged to advance knowledge on groundwater availability and quality to inform the decision about water resource protection and utilization. Therefore this study is designed to provide large-scale background information that will improve the knowledge and understanding of the Elandsfontein aquifer unit and provide a basis for potential future studies of a more-detailed nature.

Abstract

Groundwater recharge assessment was undertaken in the crystalline aquifer of the Upper Crocodile River Basin, Johannesburg South Africa. The basin is characterised by the complex hydrogeological setting represented by weathered and fractured granitic gneisses overlain by quartzite, shale and dolostone. A number of recharge estimation methods including the Stable Isotope Enrichment Shift method, were tested. The measurement of δ 18O and δD in springsrevealed the presence of high elevation recharge or cold weather recharge that occurs prior to extreme evaporation, undergoing deep circulation and discharging at the contact between the Witwatersrand quartzite and the underlying shale. In the dolostones, recharge occurs after evaporation at higher elevation undergoing deeper circulation through the dissolution cavities.

The Water Table Fluctuation method in the dolostone resulted in the mean annual recharge of 99 mm/year, representing 14% of mean annual precipitation. The Reservoir Water Balance method revealed that the Pretoria Group shale aquifer contributes 16% of dam water outflow per year (groundwater discharge) which equates to 3 429 662 m3 on average, while 7% of dam inflow is lost to groundwater constituting groundwater recharge of average 2 084 131 m3 per annum. Baseflow Separation method applied gave an average recharge value of 9.4% for the entire catchment. The estimated average recharge for the entire catchment was found to be 13% corresponding to 91 mm, which equates to 374 Mm3 . The Stable Isotope Enrichment Shift Method resulted an average annual recharge of 26.1% in the aquifers composed of quartzites and 3% in the dolostones. The method is found to be promising for application in spring regimen however, a further development is recommended since small shifts exaggerate recharge while large shifts undermine it.

Abstract

The Gravity Recovery and Climate Experiment (GRACE) satellites detect minute temporal variation in the earth's gravitational field at an extraordinary accuracy, in order to make estimation of the total water storage (TWS). GRACE provides a unique opportunity to study and monitor real time water variation in the hydrologic stores (snow, groundwater, surface water and soil moisture) due to increases or decreases in storage. The GRACE monthly TWS data are being used to estimate changes in groundwater storage in the Vaal River Basin for a period (2002 to 2014). The Vaal River Basin has been selected, because it is one of the most water stressed catchments in South Africa; it is well-renowned for its high concentration of industrial activities and urbanized zones. Therefore, in order to meet future water demands, it is critical to monitor and calculate changes in groundwater storages as an important aspect of water management, where such a resource is a key to economic development and social development. Previous studies in the Vaal River Basin were mostly localised focusing mainly on groundwater quality and to a lesser extent groundwater assessment. Hydrological models have been generated for the whole of South Africa, but many of these models do not take into account the groundwater component. Thus, there is a significant gap in the understanding of surface and ground water dynamics in the Vaal River Basin. The paucity of data and monitoring networks are often the limitation in calculating changes in water storage over a large area, particularly in Africa. In this scenario GRACE is a good approach to estimate changes in hydrological storages as it covers large areas and generates real time data. It does not require information on soil moisture, which is often difficult to measure. The accuracy of calculating change in groundwater storage lies in the processing of GRACE data and smoothing radii. For this study, smoothing radii of 1500, 900, 500, 300, 150 and 1 km are used. Currently the associated error with different smoothing radii is unknown. The preliminary results indicate that the study area experienced a loss in TWS of -31.58 mm equivalent water height over a period of 144 months in TWS at 300 km smoothing radius. The change in groundwater storage is calculated by incorporating hydrologic components to the TWS (work in progress). The results obtained from this study will be compared to existing hydrological models and results generated from models applicable to the semi-arid region of South Africa. It is anticipated that this satellite observation technique, GRACE, will provide an accurate estimate of change in groundwater storage. Furthermore, it will show the usefulness of satellite based techniques for improving our understanding of groundwater dynamics, which will improve water management practices.

Abstract

The Gravity Recovery and Climate Experiment satellites detect minute temporal variation in the earth’s gravitational field at an unprecedented accuracy, in order to make estimation of the total water storage (TWS). GRACE provides a unique opportunity to study and monitor real time water variation in the hydrologic stores( snow, groundwater, surface water and soil moisture) due to increase or decrease in storage. The GRACE monthly TWS data are used to estimate changes in groundwater storage in the Vaal River Basin. The Vaal River Basin has been selected because it is one of the most water stressed catchment in South Africa; it is well-renowned for its high concentration of industrial activities and urbanized zones. Therefore, in order to meet future water demands it is critical to monitor and calculate changes in groundwater dynamics as an important aspect of water management, where such a resource is a key to economic development and social development.

Previous studies in the Vaal River Basin, where mostly localized focusing largely on groundwater quality and to a lesser extent groundwater assessment. Hydrological models have been generated for the whole of South Africa, many of this models does not take into account the groundwater. Thus, there is a significant gap in our understanding of surface and ground water dynamics in the Vaal River Basin. The paucity of data and monitoring networks is often the limitation in calculating changes in water storage over a large area, particularly in Africa. In this scenario GRACE is the only approach to estimate changes in hydrological stores as it covers large areas and generate real time data. It does not require information on soil moisture, which is often difficult to measure. The preliminary results indicate that the change in TWS anomaly derived from GRACE data is - 12.85 mm of vertical column of water at 300 km smoothing radius. The change in groundwater storage is calculated by incorporating hydrologic components to the TWS (work in progress). The results obtained from this study will be compared to existing hydrological models and results generated from models applicable to the semi-arid region of South Africa. It is anticipated that this satellite observation technique, GRACE, will provide an accurate estimate of change in groundwater storage. Furthermore, it will show the usefulness of satellite based techniques for improving our understanding of groundwater dynamic, which will improve water management practices.