Research Articles (Earth Sciences)

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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.
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.
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.
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
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.
Groundwater discharges to aquatic ecosystems associated with the Table Mountain Group (TMG) aquifer: a conceptual model
(Water Research Commission, 2008) Roets, Wietsche; Xu, Yongxin; Raitt, Lincoln; Brendonck, Luc
This paper reports on a conceptual model that was developed to describe the different groundwater discharge ‘types’ from the Table Mountain Group (TMG) aquifer, that contributes to the different components of the flow regime in each of the recognised river reaches for streams and rivers associated with the TMG. This model integrates hydrogeological, ecological and geomorphological understandings into an ecohydrological perspective linking ground- and surface water systems. Through geospatial intersections of existing GIS layers a GIS model was also developed to highlight the quaternary catchments containing sensitive aquatic ecosystems that could be vulnerable to groundwater use from the TMG. The conceptual model demonstrates the intimate link between groundwater from the TMG aquifer and aquatic ecosystems in the mountain and foothill reaches of streams and rivers in the Cape Folded Mountains in particular. It also identifies two primary zones of interaction between groundwater and surface water in the TMG, namely, the ‘TMG aquifer daylight- domain’, located in the recharge zone, and the ‘TMG aquifer surface water interface-domain’, located at the discharge end of the aquifer. The conceptual model clearly indicates the difference between real groundwater, and perceived groundwater contributions to streamflow in the TMG. It is the lower flows of the flow regime that will be most vulnerable to groundwater use from the TMG aquifer in the ‘TMG aquifer daylight-domain’, which are unfortunately also the most important flows from an ecological perspective. However, any groundwater use from the TMG aquifer will also affect the discharge end of the aquifer, located far from the higher elevation recharge areas, or the point of groundwater abstraction, in lowland settings in the ‘TMG aquifer surface water interface-domain’. The GIS model integrated the conceptual understanding into a management tool by highlight all quaternary catchments associated with TMG containing sensitive aquatic ecosystems and gave the variable vulnerability for each.
Groundwater management issues in Southern Africa – An IWRM perspective
(Water Research Commission, 2008) Braune, Eberhard; Xu, Yongxin
In contrast to its strategic role as essential resource to help achieve community development and poverty alleviation in the Southern African Development Community (SADC), groundwater has remained a poorly understood and managed resource. This was the finding of a scoping study regarding the status of groundwater resources management in SADC. The key premise for the assessment was that groundwater resource management must take place within an IWRM framework and the IWRM Toolbox developed by the Global Water Partnership was used as the scope and content for the assessment. The SADC region has well- developed policies for regional development and IWRM, as well as a relatively strong focus on groundwater resources. This article questions whether problems relating to Africa’s sustainable utilisation and management of groundwater is a unique groundwater problem or must also be related to the challenges experienced in general with the implementation of an IWRM approach in Africa. A key finding was that groundwater management links to groundwater-dependent sectors like agriculture, rural development, health and environment are not well- established in policy or in practice. Internationally, there is a recognition, that such a, quite common, situation can only be addressed through a long-term process through which viable national, regional and local systems can evolve, within a strategic framework in which these intended relationships between diverse sets of interventions or management approaches and the development goals are brought out. However, such a strategic, multi-stakeholder-driven approach also still remains the major challenge in Africa for IWRM implementation as a whole. Recent continent-wide initiatives, like the development of IWRM and water efficiency plans for each country and multi-stakeholder water dialogue processes, have been taken to address this challenge. It is therefore crucial that groundwater becomes an integral part of these and related initiatives. New AMCOW and SADC initiatives for groundwater provide a major opportunity to achieve this.
Editor’s message: Building capacity and partnerships towards sustainable utilization of groundwater in Africa
(Springer, 2008) Xu, Yongxin
This Editor’s Message advises the international groundwater fraternity of new opportunities in hydrogeological developments in Africa. It is a fact that groundwater plays a vital role in socio-economic and ecological services in the continent but it has been largely neglected in the past. With the 6th Ordinary Session of AMCOW (African Ministers’ Council on Water) held in Brazzaville, Congo in late May 2007, the profile of groundwater in the continent has been raised.
The role of ground water in Sub-Saharan Africa
(Wiley-Blackwell, 2010) Braune, Eberhard; Xu, Yongxin
Although water resources managers speak of a water crisis in Africa, the management of ground water has to date not featured strongly in national and regional African water agendas. Examination of the physical environment of the continent and, in particular, the water resources in relation to the socioeconomic landscape and regional development challenges makes it clear that widely occurring, albeit largely low-yielding, ground water resources will be crucial in the achievement of water security and development. Ground water is important primarily in domestic water and sanitation services, but also for other local productive needs like community gardens, stock watering, and brick-making, all essential to secure a basic livelihood and thus to alleviate poverty. Despite the importance of small-scale farming in Africa, there is little information on the present and potential role of ground water in agriculture. In contrast to its socioeconomic and ecological importance, ground water has remained a poorly understood and managed resource. Widespread contamination of ground water resources is occurring, and the important environmental services of ground water are neglected. There appear to be critical shortcomings in the organizational framework and the building of institutional capacity for ground water. Addressing this challenge will require a much clearer understanding and articulation of ground water’s role and contribution to national and regional development objectives and an integrated management framework, with topdown facilitation of local actions.
Foreword to special section: groundwater in Africa
(Wiley-Blackwell, 2010) Bradbury, Kenneth R.; Xu, Yongxin
Investigating changes over time of annual rainfall in Zimbabwe
(Copernicus Publications, 2010) Mazvimavi, Dominic
There is increasing concern in southern Africa about the possible decline of rainfall as a result of global warming. Some studies concluded that average rainfall in Zimbabwe had declined by 10% or 100 mm during the last 100 years. This paper investigates the validity of the assumption that rainfall is declining in Zimbabwe. Time series of annual rainfall, and total rainfall for (a) the early part of the rainy season, October-November-December (OND), and (b) the mid to end of the rainy season, January-FebruaryMarch (JFM) are analysed for the presence of trends using the Mann-Kendall test, and for the decline or increase during years with either high or low rainfall using quantile regression analysis. The Pettitt test has also been utilized to examine the possible existence of change or break-points in the rainfall time series. The analysis has been done for 40 rainfall stations with records starting during the 1892– 1940 period and ending in 2000, and representative of all the rainfall regions.
A conceptual model for the development and management of the Cape Flats aquifer, South Africa
(Water Research Commission, 2010) Adelana, Segun; Xu, Yongxin; Vrbka, Petr
This paper provides an integrated approach to the analysis of the geological, hydrological and hydrogeological characteristics of the Cape Flats: a coastal plain sand formed within the mountains of the Cape Town metropolitan area. The study is mainly based on evaluation of available data, on surface water and groundwater, rainfall and selected springs, to describe the Cape Flats aquifer. Qualitative analysis has shown that both surface water and groundwater of the investigated area are of good quality; whereas sources of contamination indicated are restricted to certain parts of the area. Interpretation of hydrogeological data and aquifer parameters revealed that the Cape Flats aquifer has good storage characteristics to support its development for water supply, although the generally unconfined conditions render it highly susceptible to pollution from the surface. From the analysis of long-term climate data in Cape Town, it is evident that fluctuation exists in the pattern of rainfall; this rainfall pattern has implications for recharge and water management issues in the city. Therefore, a conceptual hydrogeological model was developed to elucidate groundwater flow and recharge mechanisms in the Cape Flats.
Review: groundwater management and groundwater/surface-water interaction in the context of South African water policy
(Springer Verlag, 2011) Levy, Jonathan; Xu, Yongxin
Groundwater/surface-water interaction is receiv¬ing increasing focus in Africa due to its importance to ecologic systems and sustainability. In South Africa's 1998 National Water Act (NWA), water-use licenses, including groundwater, are granted only after defining the Reserve, the amount of water needed to supply basic human needs and preserve some ecological integrity. Accurate quantification of groundwater con¬tributions to ecosystems for successful implementation of the NWA proves challenging; many of South Africa's aquifers are in heterogeneous and anisotropic fractured-rock settings. This paper reviews the current conceptualizations and investigative approaches regard¬ing groundwater/surface-water interactions in the con¬text of South African policies. Some selected pitfall experiences are emphasized. The most common approach in South Africa is estimation of average annual fluxes at the scale of fourth-order catchments (~500 km2) with base flow separation techniques and then subtracting the groundwater discharge rate from the recharge rate. This approach might be a good start, but it ignores spatial and temporal variability, potentially missing local impacts associated with production-well placement. As South Africa's NWA has already been emulated in many countries including Zambia, Zimbabwe and Kenya, the successes and failures of the South African experience dealing with the groundwater/surface-water interaction will be analyzed to guide future policy directions.
Book review: estimating groundwater recharge
(Springer Verlag, 2011) Xu, Yongxin
Assessment of microbial contamination of groundwater in upper Limphasa River catchment, located in a rural area of northern Malawi
(Water Research Commission, 2012) Kanyerere, Thokozani; Levy, Jonathan; Xu, Yongxin; Saka, John
In rural Africa, scientific evidence is often lacking to guide the scaling-up of groundwater as the safest source of potable water. An investigation was conducted in the Upper Limphasa Catchment in northern Malawi to determine the safety of groundwater sources and to explore factors influencing water quality. Water samples from 17 boreholes, 6 hand-dug wells and 90 households were analysed for selected parameters. Portable incubators, multi-parameter probe and colorimetric standard methods were used for field measurements, and standard methods were used for laboratory water analysis. Results were compared to specified guidelines of the World Health Organization and Malawi Bureau of Standards to establish the potability of water. Statistical results using non-parametric t-tests indicated that the wells were more contaminated with E. coli bacteria than boreholes (p=6.2x10-6), suggesting non-consideration of local hydrogeologic factors in groundwater development. Water from boreholes that tested negative for pathogens at source tested positive at some households (total coliform: p=0.0042 and E. coli p=7.8x10-7) suggesting the effect of handling practices. Water from wells that was not treated with chlorine showed higher levels of E. coli than treated water from the same sources, confirming the effectiveness of chlorine in reducing pathogenic bacteria in households’ stored drinking-water, reinforcing the scientific basis for scaling up chlorine as effective disinfectant. However, this study demonstrated that chlorine failed to effectively eliminate all pathogens in drinking water. As a case study in tropical rural environments in Africa, these findings on the suitability of using chlorine as disinfectant and on factors explaining groundwater contamination, though provisional, provide a scientific basis for assessing cost-effectiveness and sustainability of scaling-up the use of chlorine as a curative remedy and of systematically investigating local hydrogeologic factors in order to implement measures to protect groundwater quality in poverty-prone rural communities.

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