Department of Earth Science

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https://hdl.handle.net/10566/272

Research is organized in the broad fields of Environmental Water & Science and Applied Geology. The main research areas are in Petroleum Geology, Economic Geology/ Exploration Geochemistry, Tectonic Evolution, Integrated Water Resource Management and Groundwater studies under the leadership of the UNESCO Chair.

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A three-tier approach to protect groundwater resources in South Africa
(Water Research Commission, 1995) Xu, Yongxin; Reynders, A.G.
The quality of groundwater is affected by many activities occurring on the surface of the earth. A pro-active protection approach is required to avoid the costly and technology difficult exercise of groundwater remediation. This paper reviews various approaches for groundwater protection and documents recent developments in this field. A comprehensive protection strategy consists of many elements, ranging from the protection of entire aquifers to localized water-supply sources. A Three-tier protection concept, with the emphasis on a zoning approach, is proposed for South Africa. This will facilitate the protection of groundwater at various levels (national, regional and local) and will ensure that protection needs in the short, medium and long term are addressed.
Borehole dilution experiment in a Karoo aquifer in Bloemfontein
(Water Research Commission, 1997) Xu, Yongxin; van Tonder, Gerrit J.; van Wyk, B.; van Wyk, E.; Aleobua, B.
This paper shows that a borehole dilution experiment using common salt is a useful technique for better understanding of some hydrogeological features of a fractured aquifer. A sense of such tracer experiments was performed in the campus site aquifer, a hydrological experiment site of the Institute for Ground Studies at the University of the Orange Free State in Bloemfontein. It is demonstrated that the model for use in homogeneous aquifers may be adapted in fractured aquifers. Results have revealed valuable information on hydraulic parameters of the fracture system at different scales. Profiles of electrical conductivities monitored in several boreholes can be used to locate horizontal fracture zones in the aquifer. These results may provide an important guide to formulate realistic conceptual models for borehole protection zoning. The experiment can also serve as a reference to future experiments of this kind in Karoo aquifers which cover some 50% of the subcontinent of Southern Africa.
A water balance approach to the sustainable management of groundwater in South Africa
(Water Research Commission, 2000) Wright, K.A.; Xu, Yongxin
The water balance approach, based on the principles of conservation of mass, is applied to the issue of sustainable groundwater management in South Africa, incorporating the ethos of the National Water Act of 1998, prioritising basic human needs and the needs of aquatic ecosystems over inessential uses. The principle of water balance is described and the benefits (such as prevention of resource misallocation), of applying such an approach to groundwater management, are outlined, with additional practical considerations briefly reviewed. It is hoped that the approach will be tested and refined through application to groundwater case studies.
Estimation of recharge using a revised CRD method
(Water Research Commission, 2001) Xu, Yongxin; van Tonder, Gerrit J.
The cumulative rainfall departure (CRD) method, based on the water-balance principle, is often used for mimicking of water level fluctuations. Because of its simplicity and minimal requirement of spatial data, the CRD method has been applied widely for estimating either effective recharge or aquifer storativity, and consequently gained a focus in South Africa. This paper critically reviews this method and proposes expanded algorithm. Validation of the method under typical South African conditions is discussed based on model-generated and known cases. The study is aided with a user-friendly Excel program called Recharge Estimation Model in Excel (REME).
Capture zone simulation for boreholes located in fractured dykes using the linesink concept
(Water Research Commission, 2002) Xu, Yongxin; van Tonder, Gerrit J.
Delineation of capture zones for groundwater source protection is normally performed by using numerical codes which are based on the porous medium flow equation. However, boreholes are often sited in or along permeable dykes or single fracture zones through which aquifers are drained. It is very important to take into account dyke-influenced aquifers. This paper makes use of Linesink to simulate permeable dyke or fractured zones and utilises the pathline distribution to delineate the capture zones. Conditions when the influence of a fractured dyke can be considered negligible are also discussed through comparison with stagnation point in a uniform flow field. The approach may be sufficient to illustrate protection zoning requirements when dyke aquifers are considered.
A hydrogeomorphological approach to quantification of groundwater discharge to streams in South Africa
(Water Research Commission, 2002) Xu, Yongxin; Holness, S.D.; Zhang, J.; van Tonder, Gerrit J.
In South Africa, the flow requirements for maintaining the normal functioning of aquatic ecosystems is termed the “ecological reserve”, and these should be determined when a licence application for water allocation is processed. Determination of the ecological reserve entails investigation of the relationship between the major interactive components of the hydrologic cycle, namely groundwater and surface water bodies including rivers, lakes and estuaries. Information on groundwater discharge towards surface water bodies is critical for the water resource manager to make a decision regarding the amount of groundwater allocation that can be licensed without causing a negative impact on aquatic ecosystems. Existing techniques of hydrograph-separation are too subjective either due to the fact that assumptions of the techniques cannot be met in reality or that the parameters used in models do not have physical meanings. This paper presents a geomorphologic framework under which the quantification of groundwater from a hydrograph is discussed. A focus is placed on hydrogeomorphological typing that can be used to guide a process of separating groundwater discharge time series from hydrographs where a monthly groundwater discharge time series is required for comparison with instream flow requirements. For generating monthly groundwater discharge time series, a generic procedure is proposed, which is applied in a case study.
Hydro geochemical characteristics of the basement aquifers in namaqualand
(University of the Western Cape, 2003) Titus, R.A; Xu, Y
At the onset of this research programme it became apparent that there is a dearth of research studies focusing on the groundwater resources of the region. As a result, a conceptual representation of the hydrogeological system (i.e. specific aquifer systems, groundwater flow regime, etc.) for the perceived problematic aquifer systems in the Namaqualand region did not exist. The research project contributes significantly to conceptual representation of the aquifer system, in particular a quantitative understanding of the regions' groundwater resources in terms of its hydrochemical development and the construction of a groundwater flow model at regional scale as well as at a local scale. The groundwater resources for the Namaqualand region are developed predominantly in the basement rocks. The infiltration and flow of water is controlled by the prevailing complex fracture network and can vary in space and time. Such observations relate to structurally controlled flow systems and varying water chemistry amongst closely spaced fracture systems.
A decision-making framework for groundwater management in arid zones (with a case study in Namaqualand).
(University of the Western Cape, 2004) Pietersen, Kevin Claude; Xu,Yangwin and Green, George Clifford
The main aim of the work on which this thesis is based was to develop a framework for sustainable management of groundwater resources in arid zones with emphasis on Namaqualand in the north western region of South Africa. The first part of the thesis focuses on describing the groundwater resource base and legislative framework for groundwater management. Most aquifers in South Africa occur in fractured rock ranging in age from earliest Pre-Cambrian to Jurassic. Primary aquifers are mostly restricted to the coastal plains and river deposits. Characterisation of the fractured rock aquifers has been limited. Thus, an inadequate knowledge base exists in a number of hydrogeological domains to understand the attributes and dynamics of fractured rock aquifers. A serious shortcoming in our knowledge base is to understand the institutional arrangements necessary for proper resource management. This is particularly important in view of the National Water Act of 1998, where groundwater is subject to the same protection measures as surface water. These measures are sophisticated and require tools and technologies to be developed to support sustainable groundwater management and utilisation. The technical, economic, social, legal, political, and environmental issues affecting groundwater management of arid zones of South Africa were analysed. The objectives and appropriate measures to overcome the barriers for sustainable development were also presented. This was necessary to structure the decision problem and to generate and identify the decision alternatives. Thus decision alternatives have been formulated for the various elements of the objectives in order to achieve preferred scenarios. The main part of the thesis was the development of a decision-making framework for groundwater management in the arid zones of Namaqualand. A multiple criteria decision analysis (MCDA) approach was adopted to assist in the formulation of the decision-making framework. ln order to select the most appropriate MCDA technique, some background was required on the theoretical aspects. A value function method was selected, which provides decision support by interval SMART/SWING. This method incorporates informational uncertainty through interval judgements. The decision problem supported the selection of this method because of the discrete alternatives and uncertainty associated with groundwater management. Further, the method provided an interactive technique to interrogate various decision alternatives based on prior knowledge of the decision-maker. The software WINPRE was utilised in the value tree construction and analyses, A number of value trees and attributes were defined. These attributes were evaluated against the identified alternatives. This provided a systematic framework for the analytical understanding of the problem. As a result a number of preferred alternatives were elicited. The analyses resulted in a model for groundwater management in arid zones. The ideal state for groundwater management was presented, but in practice this is difficult to implement, mainly because of human and financial resources. As a result, a critical path was established based on the analyses done in this thesis. This was applied to the Namaqualand example. ln this example the activities to support a Catchment Management Strategy was identified. This means that the decision-maker is able to focus on issues that are deemed important. More importantly, the method allows the decision-maker to develop the various consequences of the alternatives with stakeholders. As a result of the decision model a number of strategies were proposed for sustainable groundwater management in arid zones with a case study in Namaqualand. A consequences table were developed which could be used for M&E purposes.
A comparison of SAAS and chemical monitoring of the rivers of the Lesotho Highlands Water Project
(University of the Western Cape, 2004) Rajele, Molefi Joseph; Okujeni, Charles; Jonker, Lewis; Dept. of Earth Science; Faculty of Science
The Lesotho Highlands Development Authority routinely uses the South African Scoring System version 4 (SASS4) in conjunction with water chemistry to monitor water quality of rivers in the Lesotho Highlands Water Project areas. The objective of this study was to test the efficiency of SASS4 in these areas.
Snow impact on groundwater recharge in Table Mountain Group aquifer systems with a case study of the Kommissiekraal River catchment South Africa
(Water Research Commission, 2005) Wu, Yong; Xu, Yongxin
Snowmelt in the mountainous areas of the Table Mountain Group (TMG) in South Africa is believed to be one of sources of groundwater recharge in some winter seasons. This paper provides a scientific assessment of snow impact on groundwater recharge in Table Mountain Group Aquifer Systems for the first time. Snowfall periodically occurs on the highest mountain ranges of about 1 000 to 1 200 m above mean sea level (a.m.s.l) in the TMG area. Snow over the mountainous catchments is often observed on the gentle side of the slope, which is substantially affected by wind and vegetation. Based on climatic analysis, recharge processes and Landsat 7 Enhanced Thematic Mapper (ETM) images, the recharge areas influenced by snowmelt in the TMG are identified as those catchments that are located above 1 000 m a.m.s.l. Physical processes within the snowpack are very complex involving mass and energy balances as well as heat and mass transport. Snowmelt rate was calculated using a variable degree-day melt factor determined as a function of snowpack density and vegetation cover. The hourly snowmelt rates estimated with different new snow density models. Groundwater recharge from snowmelt is affected by snowmelt mechanisms and local recharge conditions. The recharge rate is constrained by characteristics of the fractures rather than snowmelt rate. Recharge is also discounted due to prevailing interflow occurring in favourite geomorphological locations. This hypothesis is confirmed by an infiltration experiment in which up to 13.6% of the infiltrating water can recharge the aquifer.
Groundwater recharge estimation in Table Mountain Group aquifer systems with a case study of Kammanassie area
(University of the Western Cape, 2005) Wu, Yong; Xu, Yongxin; Titus, Rian; Dept. of Earth Science; Faculty of Science
The focus of this study was on recharge mechanisms and recharge estimation within the Table Mountain Group area. The study evaluated recharge processes and recharge estimation methods in the Table Mountain Group aquifer systems.
Water quality trends in the Eerste River, Western Cape, 1990 - 2005
(University of the Western Cape, 2006) Ngwenya, Faith; Jonker, Lewis; Raitt, Lincoln; Dept. of Earth Science; Faculty of Science
The Eerste River is a river system which has, over the years, been subjected to human interference. The purpose of this study was to investigatge temporal and spatial trends in the water quality of the Eerste River between 1990 and 2005. The study results revealed that the major trends in the water quality of the Eerste River are more spatial than temporal.
Hydraulic properties of the Table Mountain group (TMG) aquifers
(University of the Western Cape, 2006) Lin, Lixiang; Xu, Yongxin
The Table Mountain Group (TMG), located at the southmost cape of African Continent, is one out of three major regional aquifer systems in South Africa, which has a potential of bulk water supply to meet the requirements of irrigation and local municipalities in the Western and Eastern Cape provinces. The TMG aquifers comprising a thick sequence of hard sedimentary rocks dominated by fractured sandstones have the outcrop area of 37000 km2, the deposit area of 248000 km2 and the thickness ranging from 900m to 4000m. Large-scale distribution of the TMG over various geological structures leads to a big diversity in its hydrogeological properties, especially the hydraulic properties which are critical in determining the aquifers’ abstraction potential and sustainable yield. A proper estimation of hydraulic properties, with focus on the investigation of aquifer porosity, permeability and storativity, is important for the sound evaluation and sustainable utilization of the groundwater resource in the TMG area. Data from previous studies and current research have been collated and analyzed to help establish conceptual models of the TMG aquifers and to quantify the intrinsic aquifer properties − hydraulic properties. Based on the study of hydrogeological settings and aquifer types, combined with the interpretation of aquifer hydraulic tests, it is realized that the hydraulic properties of the TMG rocks are strongly controlled by fractures regarding the groundwater flow path within the TMG rocks. Media study on the nature of the fractures or fracture networks therefore is conducted in detail. Subsequently, the establishment of the fractured-media conceptual models on the basis of stochastic analyses is helpful for the better understanding of groundwater behaviors in the TMG aquifers. With the data derived from field measurements and interpretation of remote sensing data, the fractured rock hydraulic conductivities are estimated by using a hydraulic conductivity tensor approach. Considering the influential factors such aperture, roughness, stress condition, and most importantly the connectivity of fractures, the tensor model is accordingly modified to meet different boundary conditions for the estimation of the hydraulic conductivities on the surface and at depth. As a result, the estimated hydraulic conductivities at most sites fall in the range of 10-2~10-3 m/d that is roughly consistent with site pumping test results. However, it decreases with depth following a negative power law, which implies that the majority of fractures tend to be closed at depth. Site hydraulic tests also show the similar tendency of vertically spatial variation of the hydraulic conductivities. The study of fracture connectivity shows another hydrogeological significance. Fracture networks on the measurement scale present the feature of various fracture blocks in the system rather than they are well connected. The 3-D model demonstrates that very few fractures in the TMG sandstones are competent for groundwater flow. With this regard the computation of hydraulic conductivities is hence calibrated Multiple approaches are employed to estimate porosity and associated aquifer storativity. Results show that porosity of the TMG sandstones is strongly scale-dependent, of which the value of core sample laboratory tests yield a upper limit of 1.0%~3.6%. The porosity of pumping tests and in-situ fracture measurements fall in the middle rang of 0.05%~0.6%, whilst the application of lineament interpretation from remote sensing data produce its lower limit of 1.2×10-8. Assuming the TMG rocks are homogeneous media, the storativity value should have the same trend at various scales. These results indicate that the TMG groundwater resource at a larger scale may be overestimated if use the aquifer parameters derived from a smaller-scale study. Research findings in current study provide a new insight into the fractured rock aquifers in the TMG area. Some of the results will have wide implications on the groundwater management and forms a solid basis the further study of the TMG aquifers.
Sustainable groundwater use, the capture principle, and adaptive management
(Water Research Commission, 2006) Seward, Paul; Xu, Yongxin; Brendonck, Luc
The purpose of this paper is to review the case for using ‘capture’ rather than recharge as the conceptual basis for sustainable groundwater use in South Africa. Capture refers to the sum of the increase in recharge and decrease in discharge brought about by pumping. Definitions of sustainability are reviewed, and the capture process is outlined. Implications for using the capture principle in the implementation of the NWA are discussed, and adaptive management is proposed as an appropriate management approach. Implications for groundwater monitoring are also discussed. Case studies are described that support the need for adaptive management and the application of the capture principle
Pre-paid water metering: social experiences and lessons learned from Klipheuwel pilot project, South Africa
(University of the Western Cape, 2006) Kumwenda, Moses; Jonker, L; Dept. of Earth Science; Faculty of Science
This thesis examined a pre-paid water metering pilot project which was implemented in Klipheuwel , Cape Town, South Africa in 2001. It was anticipated that the implementation of pre-paid water meters would help improve the management of water service delivery in the Cape Metropolitan Area. However, just four years after its implementation the project has collapsed.
A tensor approach to the estimation of hydraulic conductivities in Table Mountain Group aquifers of South Africa
(Water Research Commission, 2006) Lin, Lixiang; Xu, Yongxin
Based on the field measurements of the physical properties of fractured rocks, the anisotropic properties of hydraulic conductivity (HC) of the fractured rock aquifer can be assessed and presented using a tensor approach called hydraulic conductivity tensor. Three types of HC values, namely point value, axial value and flow direction one, are derived for their possible applications. The HC values computed from the data measured on the weathered or disturbed zones of rock outcrops tend to give the upper limit values. To simulate realistic variations of the hydraulic property in a fractured rock aquifer, two correction coefficients, i.e. the fracture roughness and combined stress conditions, are adapted to calibrate the tensor model application. The application results in the Table Mountain Group (TMG) aquifers show that the relationship between the HC value and fracture burial depths follows an exponential form with the power hyperbola.
Realizing agricultural potential in land reform: The case of Vaalharts irrigation scheme in the Northern Cape Province
(University of the Western Cape, 2007) Maisela, Ramatsimele Jacqueline; Lahiff, Edward; Faculty of Economics and Management Sciences
The effectiveness of the South African Land reform Programme has been at the centre of debates amonng land reform activists and within government. Empirical evidence shows that land reform has not only been moving at a slow pace, but has also had limited impact on the livelihoods of beneficiaries, due to the fact that many land reform farms have operated at a very low level since being transferred to their new owners. This study looks at performance of land reform in South Africa, using the Vaalharts Irrigation Scheme in the Nothern Cape as an example.
Groundwater resource evaluation in Table Mountain group aquifer systems
(University of the Western Cape, 2007) Jia, Haili; Xu, Yongxin; Titus, Rian; Dept. of Earth Science; Faculty of Science
Table Muntain Group has been identified as one of the major Regional Aquifers in South Africa. the vast distribution of it leads to a great diversity in its hydrogeological properties, which influences the dynamics of recharge, discahrge and storage, resulting in groundwater occurrances unevenly distributed in TMG area. Thereby a proper regional groundwater resource evaluation focusing on the quantification of recharge, discharge and storage, is of most importance for the efficient groundwater utilization and management of TMG aquifers.The response of TMG aquifer to pumping stress is studied in Kammanassie Mountains by groundwater flow modeling. 3D hydrogeological model is constructed, which helps to improve the understanding of the conceptual hydrogeological model. Detailed groundwater-related analyses are performed on the basis of previous data sets. Groundwater numerical model is then established according to the conceptual model to stimulate the aquifers responses to various pumping scenarios. Some general data processing approaches are also develooped in this study that can be expected to apply to analog studies.
Conservation status of large branchiopods in the Western Cape, South Africa
(Springer Verlag, 2007) De Roeck, Els R.; VanSchoenwinkel, Bram J.; Day, Jenny A.; Xu, Yongxin; Raitt, Lincoln; Brendonck, Luc
Temporary wetlands are an ecologically and economically important habitat in South Africa. They harbor large branchiopods, known to be flagship species of nonpermanent aquatic habitats, and sensitive to land use changes. In this study we review the current status of large branchiopods in the Western Cape, a South African province subject to increasing agriculture and urbanization. We studied the species diversity and distribution of large branchiopods by sampling 58 temporary wetlands in an area covering about 30% of the Western Cape. Information obtained from field samples was supplemented by incubating resting egg banks from the sampled wetlands. Our data were compared with all known distribution records for large branchiopods in the target region. Based on this combined information, the International Union for the Conservation of Nature and Natural Resources (IUCN) Red List category was assessed for each species. Four of the eight large branchiopod species known to occur in the sampling area were collected. Of all wetlands sampled, 40% harbored large branchiopods. Most anostracan populations were small, and species co-occurred in only one wetland. From the entire Western Cape, 14 species have been recorded in the past. Two of these are already included in the IUCN Red List. Insufficient data are available to determine the IUCN Red Data Category of six other species. A large variation in the telsonic appendages of S. dendyi was found across the studied area. In view of possible ongoing speciation and subsequent radiation, individual populations need protection. Since little information is available, it is difficult to evaluate recent changes in the conservation status of large branchiopods. Their populations are currently very low and have probably diminished in the last few decades. More knowledge about the functioning of temporary systems is needed to manage these vulnerable habitats and conserve their threatened species.
Empowered women in water management
(University of the Western Cape, 2007) Zonde, Memory; Jonker, Lewis; Abrahams, Yvette; Faculty of Science
Following South Africa's independence from apartheid rule, there has been progressive developments in policies that promote equity in all spheres including the water sector. Equality in the water sector is not only limited to water access, but also management of the water. This study investigated the factors that empower women in the water sector as an example of gender equity.

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