Conference Abstracts

All Abstracts were presented at the Groundwater Conferences

Displaying 1 - 10 of 220 results
Title Presenter Name Presenter Surname Area Conference year Keywords

Abstract

Veltman, S

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

The South African government is considering shale gas extraction in the Karoo basin, South Africa. To protect groundwater resources, there is an urgent need to do a groundwater baseline in possible gas extraction areas. Various groundwater samples have therefore been taken at a borehole and 2 soekor wells in the Northern Cape, from 2016 to 2021. The groundwater samples were analysed for dissolved gasses, specifically focussing on methane. As laboratories became more efficient ethane was also included in later analyses. From the analyses we found that drought might influence the dissolved gas concentrations in the groundwater via pressure influences on the groundwater flow and the dissolved gas flow towards the shallow aquifers. Artesian conditions at this site are helping with the flow of dissolved gasses from deep to shallow aquifers via preferential pathways. The possibility of shallow-deep groundwater interconnections and the migration of deep methane to shallow aquifers make it important to establish a groundwater baseline in the Karoo. By focusing on boreholes and wells that are emitting methane, a better understanding of groundwater flow and interaction with geological layers can be determined. If other gasses like propane and butane can be analysed in addition to methane, more information can be gathered to determine the origins of the methane and whether it is thermogenic or biogenic.

Abstract

Saldanha Bay Local Municipality appointed Skytem to conduct an airborne geophysical 3D aquifer mapping survey. As part of improving the sustainable management of the groundwater resources and exploring the options of Managed Aquifer Recharge, a better understanding of the aquifers is required. The Skytem technology unlocked a rich understanding of the subsurface geology and the groundwater contained in it.

Before the main survey commenced, a trial survey was conducted to investigate the quality of the data that may be expected from the main survey. The trial survey was conducted over the existing water supply wellfield where there were existing groundwater data including borehole lithology from drilling and ground geophysics. Consequently, the main survey commenced and consisted of the following:
1) Magnetic survey providing information regarding bedrock composition and where it changes due to faults or deposition,
2) Time Domain Electromagnetic survey providing conductivity/resistivity of the subsurface,
3) Detailed elevation along flight paths, and
4) 50Hz signal to understand where interferences can be due to power lines.

The survey interpretation showed the following important aquifer characteristics that will be useful for future management of the aquifer system:
1) Bedrock elevation and paleo topography, 2) Areas with different bedrock composition, 3) Geological faults in the bedrock, 4) Bedrock below the surface, 5) Areas with thick dry sand, 6) Clay layer extent and area without clay, 7) Areas with different water quality, and 8) Areas with very high concentrations of salt.

The survey output and interpretations are regarded as very useful for the update of the conceptual models for the area. Data can now be used to update the numerical models and improve the management of the wellfields.

Abstract

Chow,  R; Watson, A

The frequency, intensity, and duration of droughts are increasing globally, putting severe pressure on water supply systems worldwide. The Western Cape Province suffered from a period of severe water shortages that began around January 2015 and lasted until about July 2018. During this recent drought, there was a forced reduction in water use, predominantly from the agricultural sector. Citizens also reduced water use and increasingly tapped into groundwater for their needs irrespective of whether the hydrogeology was considered favourable or not. Unmonitored and unregulated abstraction of groundwater, especially under unstable climatic conditions, poses a significant risk to the future water security of the Western Cape.
We hypothesize that groundwater enabled the municipalities, residents, and industries of the Western Cape to survive the recent drought. Our aim is to evaluate the change in groundwater storage during the 2015 to 2018 drought and its subsequent recovery. To achieve this, we must gain a comprehensive understanding of the dynamics of separate components of the water cycle, as well as the overall water balance.

While there is data on surface water use during the drought, the impact on groundwater resources has yet to be evaluated. However, the accurate assessment of groundwater use is difficult, especially in data-scarce regions, such as South Africa. In our study, we combine remote sensing from NASA’s Gravity Recovery and Climate Experiment (GRACE), the Global Land Data Assimilation Systems, groundwater level measurements from the National Groundwater Archive, and ancillary datasets from the City of Cape Town’s weekly water dashboard to assess the total change in groundwater storage in the Cape Town Metropolitan area and surrounding cities over an 8-year period, from 2012 to 2020. Preliminary results from GRACE data analysis show a steady decline in aquifer saturated thickness over the drought, indicative of an increase in groundwater use.

Abstract

With increasing population growth and a subsequently increased demand for food production, the agricultural sector has had to grow and develop continuously despite drought-stricken water resources in recent years. The expansion in this sector requires increasingly efficient water use management and increases in water supplies, which are often met through groundwater utilization. In the past several years the use of groundwater in the Western Cape has increased exponentially and thus has forced the sharing of resources. The question pertains to how an invisible water resource that is difficult to measure and quantify, can be shared. Issues of varying complexities can arise when submitting a water use licence application (WULA), such as historical water use debates, interactions between groundwater and surface water, seasonal stresses on resources, etc. In one case study in De Doorns, a WULA became side-tracked soon after initiation by a neighbour’s complaint that his production borehole was severely affected by the drilling of the applicant’s boreholes. In the second case study in the Hexriver Valley, a WULA was complicated by a gentleman’s agreement stating that no one in the valley is allowed to abstract groundwater from deeper than 6 m. This gentleman’s agreement stems from past disagreements regarding such practices. The final case study was not a WULA but arose out of concerns for dropping weir levels connected to a new borehole. The borehole was equipped with new casing to case off the alluvium; it was suspected to be the cause of the disturbance. The scientific method was used to evaluate the borehole’s impact on the weir. Case studies such as these will become more prevalent as the demand on water resources will increase. Hydrogeologists needs to more informed of the complexities that can and will arise in the future as a result of shared water resources.

Abstract

The western part of South Africa is experiencing a prolonged drought. In many cases, the effects of drought have been noticed since 2011, putting the western part of the Northern Cape under severe stress to provide water to the communities. In the past 10 years, rainfall has also decreased, and in most cases, the catchments did not receive rain to help with the recharge of groundwater. Various lessons were learned from the change in the climate and environment. But a lot can be done to minimise the impact of these changes on the water supply to communities. This paper addresses what we are noticing in the environment that impacts the way we think groundwater behaves. The changes include the change in rainfall: patterns, lines, and type of rainfall. The collapsing of boreholes with water strikes closing when being over-pumped occurs more often in the last 3 years. Pump test recommendation changes with water level change – deployment output. A combination of the factors mentioned puts more stress on groundwater resources, and a mindset change is needed to give assurance of future supply to the communities.

Abstract

The impact of the future closure of the KROPZ phosphate mine in the West Coast on the various potential receptors including the underlying Elandsfontein Aquifer System (EAS), Langebaan Lagoon (RAMSAR-site) and wetlands were assessed. This abstract/paper describes the geochemical characterization and management options related to the waste streams from the mining activity, to assess the post closure contribution to groundwater flow from the mine towards potential receptors. The PHREEQC geochemical modelling code was used to predict potential mine water impacts. The input water quality parameters used in the model included: background groundwater quality, pit water and processed water generated from phosphate separation process at the mine. Various scenarios were simulated combining the different process water streams with the tailings and soft stockpile material at the mine. The geochemical predictions showed some management options that should be prevented, while also providing guidance to promising options where most of the chemical parameters does not exceed the WUL stage 1 thresholds. There is however, an increase in sulphate concentrations that need attending to before the mine goes into production phase. Currently there seems to be no immediate concern on the Lagoon relating to the prediction of mine water impacts post mine closure. Some of the management scenarios do however show low levels of potential impacts on SANParks property 100 years post closure. These predictions do however correlate to areas where limited calibration data is available. At the time of this abstract the sites for new boreholes have been selected and the initial boreholes are being drilled to confirm aquifer properties in areas with limited data.

Abstract

Israel,S

Surface water resources are under threat of depletion and quality deterioration due to various factors such as climate change, urbanization, and population expansion. Managed aquifer recharge (MAR) is a technique that has been successfully implemented over the last 4 decades to sustain the balance between water demand and availability. The unsaturated zone, where source water is introduced during infiltration, plays a major role in the reduction of contaminants present in water before it naturally percolates and reaches the aquifer. This research aims to evaluate the removal efficiency of contaminants by the unsaturated zone. Three objectives to be accomplished are; to determine and classify the chemical composition of the source water. Secondly, to determine the hydraulic properties of the soil in the area of interest. Lastly to evaluate the contaminants removal efficiency, by tracing the quality of water at the point of recharge and discharge. The Atlantis water resource management scheme in the Western Cape will be used as a case study, in order to assess the relationship between the unsaturated zone and the reduction of contaminants. The current study argues that during the artificial recharge of aquifers, contaminants present in the source water filter through the unsaturated zone, where natural processes, as well as resident microbes, reduce their concentrations to acceptable levels. Assessing the ability of the unsaturated zone to reduce contaminants, will allow for the early warnings of contamination potential and the execution of informed prevention strategies that can be used in decision making of the management and protection of water resources. Additionally, the advanced understanding of the role that the unsaturated zone plays in eliminating contaminants can be used to account for satisfactory groundwater quality in areas where groundwater is not constantly monitored and artificial remedies are not applied.

Abstract

In response to the serious 2015-2018 “Day Zero” drought, the City of Cape Town implemented large-scale augmentation of the Western Cape Water Supply System from deep groundwater resources within the Table Mountain Group (TMG) fractured aquifers. Several planned TMG wellfields target the Steenbras-Brandvlei Mega-fault Zone (SBMZ), the northern segment of which hosts the Brandvlei hot spring (BHS) – the hottest (~70°C) and strongest (~4 million m3/yr) in the Western Cape. Considering its possible “neohydrotectonic” origin, the BHS may mark the site of a major palaeo-earthquake, suggesting that SBMZ structures are prone to failure in the current crustal stress regime. Despite the “stable” intraplate tectonic setting, the SW Cape has experienced historic large (magnitude >6) earthquakes. Therefore, a better hydrogeological and seismotectonic understanding of the regional “mega-fault” structures is needed.

The South African TrigNet array of continuously recording Global Navigational Satellite System (GNSS) stations can be used to measure surface deformation related to confined aquifer depressurisation and vertical compression during groundwater abstraction. Time-series data from 12 TrigNet stations were used to establish a monitoring baseline for the SW Cape. Observed vertical motions range from slow subsidence to variable slow uplift with superimposed cyclical uplift/depression patterns of seasonal and multi-year variability. Baseline deformation/strain rates were calculated using 27 station pair lengths, ranging between compressive (-0.47 nanostrains/yr) and extensive limits (+0.58 ns/yr), indicating a rigid intraplate setting.

Anomalous high strain rates (> 10 ns/yr), associated with three stations, are probably due to station mount/foundation issues, rather than neo-seismic activity. Regional results show that seismo-geodetic monitoring is an important tool for understanding fractured aquifer compressibility and hydroseismicity, the latter of which may potentially be induced by large-scale TMG groundwater abstraction and/or natural earthquakes in the Western Cape. A local seismo-geodetic monitoring system is therefore being established at Steenbras Wellfield for further observations and analysis.

Abstract

Kanyerere, T

The argument in this paper is that improved understanding of science-policy integration, where physical bases of natural science is combined with practice in managing water resource challenges, becomes critical in translating scientific knowledge into effective and sustainability solutions linked to groundwater resource protection. Such hypothesis should be attested at locally relevant scale where water resources reside and where water utilization takes place. This paper provides a practical case-study of how science-policy integration can directly impacts groundwater resource protection practice from a local, and national perspective using strategies of groundwater resources directed measures. A combination of literature surveys, and desktop record review methods were used for the purpose of data collection from published literature and publicly accessible national databases of the Department of Water and Sanitation (DWS). Collected data were analysed using document analysis, descriptive statistics, and case study analysis methods. Based on the analysis, three types of science-policy nexus theoretical models exist in practice, namely, 1) science-policy integration, 2) policy-science integration, and 3) mixed integration. From a national perspective, the analysis showed that South Africa is able to practically apply science-policy nexus in policy implementation practice for water resources protection, and that such practice depicts a mixed integration model of the nexus. Case study analysis of the Schoonspruit-Koekemoerspruit River Catchment provided insight on how localized operationalization of groundwater resource directed measures facilitates sustained groundwater resources protection for water availability and sustainable utilization. This study provides an exemplary for collaborations between researchers and/or scientists and policy makers to ensure that science research is answering policy-relevant questions and that results from scientific work are readily available for policy implementation. In addition, there is adequate evidence to indicate that science-policy nexus can be designed and prioritized to support sustainable development agenda on groundwater resilience, and visibility at various levels.