Scielo RSS <![CDATA[Water SA]]> http://www.scielo.org.za/rss.php?pid=1816-795020160004&lang=pt vol. 42 num. 4 lang. pt <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>Movement of contaminants in the unsaturated zone of the subsurface from a low flush on-site sanitation system in Ivory Park, Johannesburg</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502016000400001&lng=pt&nrm=iso&tlng=pt This study measured the movement of contaminants in the unsaturated zone of the subsurface from a low-flush on-site sanitation system (also known as an aqua-privy) at three sites in Ivory Park, which at the time that the fieldwork was done was a newly-established informal settlement in Johannesburg. The aim of the study was to provide field data on the movement of contaminants from this sanitation system in a low-income area, in these climatic and subsurface conditions, and to counter a perception that on-site sanitation will inevitably cause pollution. Subsurface conditions consisted nominally of a 1 m thick layer of silty sand with denser gravel at the bottom of it, underlain by a stiff sandy clay (residual granite), with the natural water table more than 15 m below ground surface. In summary, it can be deduced that movement in the unsaturated zone of bacterial indicators, nitrogen and phosphorus from low-flush on-site sanitation systems in low-income areas is very limited, as long as the effluent remains in the subsurface. More specifically, the impact in terms of COD appears to be negligible, with substantial treatment apparently taking place within the soakaway or within the immediate vicinity thereof. With respect to (i) bacteriological indicators, (ii) nitrogen (in the form of ammonium, nitrite and nitrate) and (iii) phosphorus (in the form of Total Phosphorus), using the distilled water washout technique, there is a very rapid drop-off of contamination with distance from the soakaway. At horizontal distances of 3 m from the soakaway, levels of the measured contaminants had dropped to values consistent with the background levels. The results of this study are not confined to this particular sanitation system. By virtue of the higher hydraulic loading, these results provide an upper bound for contaminant movement from dry on-site systems under similar conditions. <![CDATA[<b>Water quality as bio-cultural screening indicator for the integrity of informal heritage sites</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502016000400002&lng=pt&nrm=iso&tlng=pt At informal heritage sites, a complex mutually-detrimental interaction or 'cycle of risk' between human, animal and ecological risk factors was detected where water quality is representative of ecological risk and cultural practices associated with the heritage intrinsic to sites are indicative of human risk. Informal heritage sites are therefore especially vulnerable as they are actively utilised, but not formally protected or sustainably managed. In South Africa, biomonitoring methods are used nationally for a rapid assessment of aquatic ecosystem health, subsuming a number of index models. There are six index models wherein water quality is ensconced. Of these the Physico-chemical Driver Assessment Index (PAI) is more complex and comprehensive than the others and therefore not conventionally the most rapid application. In addition, the Health Impact Assessment (HIA) was developed recently to measure the community health of people. Despite its complexity, water quality as part of the PAI was found to be the most appropriate of the available biomonitoring indices and, in this context, the most productive indicator for the cultural heritage-ecology interaction at informal heritage sites. This is based on the fact that potable water is such a fundamental human need and intricately interwoven with ritual cultural practice. The objective of the study was therefore to propose a biomonitoring model to explore the integrity of informal heritage sites where integrity encapsulates the environmental health and the authenticity of cultural practice as heritage. The authors conceived a 'bio-cultural screening' model and explored water quality as primary indicator, where water quality comprises biological (algal, bacterial), chemical (oxygen, pH, TDS, phosphorus, nitrogen, carbon, chlorophyll-a) and physical (temperature, turbidity) analyses. This method is then put forward as the Rapid Integrity Appraisal (RIA) for informal heritage sites, which may lead to the further application of other biomonitoring indices to these sites should a more nuanced exploration of the integrity of specific sites be required. <![CDATA[<b>A feasibility and implementation model of small-scale hydropower development for rural electrification in South Africa: A case study of Kwa Madiba SSHP Plant</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502016000400003&lng=pt&nrm=iso&tlng=pt Large numbers of households and communities will not be connected to the national electricity grid for the foreseeable future due to high cost of transmission and distribution systems to remote communities and the relatively low electricity demand within rural communities. Small-scale hydropower used to play a very important role in the provision of energy to urban and rural areas of South Africa. The national electricity grid, however, expanded and offered cheap, coal-generated electricity and a large number of hydropower systems were decommissioned. In this study, a feasibility and implementation model was developed to assist in designing and financially evaluating small-scale hydropower (SSHP) plants. The implementation model describes steps to be followed in identifying a technically possible and economically feasible opportunity to develop a SSHP site for rural electrification. The development model was used in designing the Kwa Madiba SSHP plant. The Kwa Madiba SSHP plant was economically evaluated on net present value, internal rate of return, levelised cost of energy, financial payback period and cost/benefit ratio. The outcome of this study proved that it is technically possible to provide SSHP installations for rural electrification in South Africa that are more feasible than local or national electricity grid extensions or even alternative energy sources such as diesel generators. It was concluded that the levelised cost of SSHP projects indicates that the cost of SSHP for low energy generation is high compared to levelised cost of coal-fired power generation. However, the remoteness of SSHP for rural electrification increases the cost of infrastructure to connect remote rural communities to the national electricity grid. This provides a low cost/benefit ratio and renders technically implementable SSHP projects for rural electrification feasible on this basis. <![CDATA[<b>Modelling the economic trade-offs of irrigation pipeline investments for improved energy management</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502016000400004&lng=pt&nrm=iso&tlng=pt Higher electricity tariffs have accentuated the importance of the trade-off between lowering investment cost by buying pipes with smaller diameters and the higher operating costs that result from the increased power requirement to overcome the higher friction losses of the thinner pipes. The Soil Water Irrigation Planning and Energy Management (SWIP-E) mathematical programming model was developed and applied in this paper to provide decision support regarding the optimal mainline pipe diameter, irrigation system delivery capacity and size of the irrigation system. SWIP-E unifies the interrelated linkages between mainline pipe diameter choice and the timing of irrigation events in conjunction with time-of-use electricity tariffs. The results showed that the large centre pivot resulted in higher net present values than the smaller centre pivot and the lower delivery capacities were more profitable than higher delivery capacities. More intense management is, however, necessary for delivery capacities lower than 12 mm-d-1 to minimise irrigation during peak timeslots. Variable electricity costs are highly dependent on the interaction between kilowatt requirement and irrigation hours. For the large centre pivot the interaction is dominated by changes in kilowatt whereas the effect of irrigation hours in relation to kilowatts is more important for smaller pivots. Optimised friction loss expressed as a percentage of the length of the pipeline was below 0.6%, which is much lower than the design norm of 1.5% that is endorsed by the South African Irrigation Institute. The main conclusion is that care should be taken when applying the friction loss norm when sizing irrigation mainlines because the norm will result in pipe diameters that are too small, consequently resulting in increased lifecycle operating costs. A clear need for the revision of the friction loss design norm was identified by this research. <![CDATA[<b>Diatom-based water quality monitoring in southern Africa: challenges and future prospects</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502016000400005&lng=pt&nrm=iso&tlng=pt Diatoms are of significant ecological importance in aquatic ecosystems, which stems from their dynamic position at the base of the trophic web as primary producers. Because diatom communities have specific environmental requirements and respond rapidly to changes in environmental conditions they are often employed as a cost-effective method to assess anthropogenic impacts and health statuses of aquatic ecosystems, particularly in Europe and North America. The purpose of this review is to summarise the challenges and future prospects associated with biological water quality monitoring using diatoms with special focus on southern Africa. Much work still needs to be carried out on diatom tolerances, ecological preferences and ecophysiology. It is recommended that past research pertaining to African diatom taxonomy should be made readily accessible to all through electronic media for use as a reference point. Moreover, following the same approach as for macroinvertebrate biomonitoring, African and other developing countries can resort to intermediate diatom taxonomy (i.e. genus), which is easier, less time-consuming and requires less-skilled personnel. While the lack of capacity and baseline information on diatom community composition and ecological requirements represent significant hurdles, diatom biomonitoring potentially holds much promise for understanding the ecological functioning and management of aquatic ecosystems in southern Africa. The application of diatom-based water quality assessment protocols has direct and immediate value for use as an 'added-value' assessment tool in addition to the use of macroinvertebrates and fish indices as these can indicate anthropogenically impacted and pristine sites. <![CDATA[<b>Testing household disinfectants for the inactivation of helminth eggs on surfaces and in spills during pit latrine emptying</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502016000400006&lng=pt&nrm=iso&tlng=pt The lack of potable water, poor hygiene practices and inefficient sanitation systems in developing countries pose a risk to human health. Pit latrines aim to break the link between human faecal waste and human contact by serving as improved sanitation. The eThekwini Municipality has developed a programme that employs workers to empty pits every 3 to 5 years. This study aimed to find a cost-effective, easy way of disinfecting household surfaces and inactivating Ascaris eggs using household disinfectants, so that transmission of helminths is minimised when pits are emptied. Disinfectants tested in this study were based on sodium hypochlorite or carbolic acid. Experiments simulated inactivation of Ascaris eggs by wiping contaminated surfaces with disinfectants and by soaking small spills in disinfectants. Samples were processed using standard helminth egg enumeration methods for soil and sludge. Wiping of contaminated surfaces removed Ascaris eggs, facilitating egg transfer but not egg inactivation. Prolonged exposure to disinfectants, at concentrations of 50% and above, were required to inactivate eggs. Sodium hypochlorite-based disinfectants were the most successful for inactivation, whilst those based on carbolic acid were mostly ineffective. It is recommended that faecal sludge spills are soaked in a sodium hypochlorite-based disinfectant and contaminated surfaces be wiped with a sodium hypochlorite-based disinfectant-saturated cloth, which should then be soaked for 1 h in a similar disinfectant solution (50% dilution) to inactivate any eggs picked up on the cloth. <![CDATA[<b>Missing the link: urban stormwater quality and resident behaviour</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502016000400007&lng=pt&nrm=iso&tlng=pt Conventional urban drainage systems are designed to reinforce human dominance over the biophysical environment resulting in contaminated surface runoff being discharged into urban waterways. It is widely recognized that poor stormwater quality is one of the main contributing factors to the deterioration of urban rivers. The result is that blue-green corridors of urban open spaces are compromised by the cumulative impacts of pollution that alter productive ecosystem services and are no longer able to support biodiversity. The problem is partly caused by conventional stormwater infrastructure, which is designed to remove runoff as quickly and efficiently as possible. Yet the condition of an urban waterway cannot be understood simply as a cause and effect relationship, but emerges from interactions between people, drainage and ecological systems. This study aimed to understand the linkage between biophysical and social systems in an urban setting in Cape Town, South Africa. Surface water flowing into roadside catchpits was analysed using multiple water quality parameters. Surveys, interviews and observations explored how local residents understand their impacts on the quality of an urban river. The results show that runoff is highly variable and some environmental conditions, such as rainfall, antecedent dry days and season, are the primary drivers of water quality. However, residents have a poor understanding of the linkages between what they do on the land and impacts on urban rivers. The findings suggest that the predominant focus on technological solutions and flood prevention do not persuade citizens to account for actions that result in deterioration of waterway conditions. Drainage infrastructure fails to connect citizens with their downstream impacts on environmental systems and services. The implication is that most residents 'miss the link' - between their actions on land, their impacts on runoff and river water quality, and, in turn, their ability to influence societal patterns and processes. <![CDATA[<b>Four decades of water recycling in Atlantis (Western Cape, South Africa): Past, present and future</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502016000400008&lng=pt&nrm=iso&tlng=pt The primary aquifer at Atlantis (Western Cape, South Africa) is ideally suited for water supply and the indirect recycling of urban stormwater runoff and treated domestic wastewater for potable purposes. The relatively thin, sloping aquifer requires careful management of the artificial recharge and abstraction for balancing water levels. Water quality management is a further key issue at Atlantis for ensuring the highest quality potable water. Groundwater quality varies from point to point in the aquifer, while urban runoff and wastewater qualities vary greatly. The layout of the town allows for the separation of stormwater from the residential and industrial areas as well as separate treatment of domestic and industrial wastewater. This permits safe artificial recharge of the various water quality portions at different points in the aquifer, either for recycling or for preventing seawater intrusion. All of the management actions are dependent on detailed data collection and this paper describes the various parts of the system, describes the data collection activities, and provides results of the monitoring and aquifer responses over the past four decades. Challenges related to iron fouling of production boreholes are also described. The presence of emerging contaminants was studied in 2008 but requires follow-up research for establishing the extent of any possible threat to water recycling. In order to address the shortcomings of the system a risk management plan based on the Hazard Analysis and Critical Control Points approach was developed. Lessons learnt from the Atlantis experience can be transferred to other potential sites for establishment of similar systems in arid and semi-arid areas of South Africa and the African continent. <![CDATA[<b>Pollutant removal in subsurface wastewater infiltration systems with/without intermittent aeration under different organic pollutant loadings</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502016000400009&lng=pt&nrm=iso&tlng=pt Organic pollutant and nitrogen removal performance of subsurface wastewater infiltration systems (SWISs) with and without intermittent aeration, and operated under different organic pollutant loadings, was investigated. The intermittent aeration strategy not only significantly increased removal rates of organic pollutants and NH4+-N, but also successfully created aerobic conditions at a depth of 50 cm and did not change anoxic or anaerobic conditions at a depth of 80 and 110 cm, resulting in high TN removal. Increasing organic pollutant loading did not affect the removal of organic pollutants and nitrogen in intermittent aerated SWISs. High removal rates of COD (98.0%~98.4%), NH4+-N (93.8%~98.1%) and TN (84.5%~94.0%) were simultaneously obtained in intermittent aerated SWISs for organic pollutant loadings ranging from 7.4 to 29.1 g COD/(m²∙d), and these removal rates were significantly higher than for non-aerated SWISs. The results suggest that intermittent aeration is a reliable option to achieve high nitrogen removal in SWISs, especially with high organic pollutant loading. <![CDATA[<b>A qualitative and quantitative analysis of historic commercial fisheries in the Free State Province in South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502016000400010&lng=pt&nrm=iso&tlng=pt There is a general lack of information on inland commercial fisheries in South Africa. The primary objective of this study was to provide a retrospective assessment of commercial fisheries in the Free State Province based on the assessment of catch data from fisheries operating for the period 1979-2014. Permits were issued for commercial operators on 11 dams but catch data were only available for Bloemhof, Kalkfontein, Gariep, Vaal, Erfenis, Rustfontein and Koppies Dams. A total of 9 036 t of fish were harvested over the 35-year period, equating to an average (± SE) of 282 ± 185 t∙yr-1. Catch composition differed between dams but comprised mainly of common carp Cyprinus carpio and the Labeos, Labeo capensis and Labeo umbratus. Based on an assessment of the available catch data, the only successful fisheries that were sustained for more than 10 years were on Bloemhof Dam (mean ± S.E.: 201 ± 25 t∙yr-1 since 1981) and Kalkfontein Dam, where 127 ± 30 t-yr-1 was harvested (by an operator from Bloemhof Dam). All other fisheries appear to have failed with individual enterprises lasting between 1 and 10 years and generally yielding less than 25 tyr-1 when operational. Success at Bloemhof Dam appears to have been dependent on the ability to harvest > 100 t∙yr-1 and the long-term fisheries experience of the operators. <![CDATA[<b>The effectiveness of conventional water treatment in removing <i>Ceratium furcoides </i>(Levander) Langhans, <i>Microcystis </i>sp. and microcystins</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502016000400011&lng=pt&nrm=iso&tlng=pt Algal blooms are a global problem due to various negative effects that can compromise water quality, such as the production of metabolites that are responsible for odour, colour, taste and toxins. In drinking water supplies algae can reduce the aesthetics of potable water when not readily removed by conventional water treatment processes. One of the major challenges in water treatment is the removal of cells without leading to lysis and the consequent release of dissolved metabolites in the water. The Maestra Reservoir, which is located in Caxias do Sul, RS - Brazil, is a small meso- to supereutrophic reservoir. The reservoir provides water for the Celeste Gobatto water treatment plant (Celeste Gobatto WTP) which uses the conventional method of treatment. This study aimed to evaluate the efficacy of conventional water treatment for the removal of algae, cyanobacteria and cyanotoxins. A bloom of Microcystis (Kützing) ex Lemmermann with a density of 23 163 cells-mL-1, Ceratium furcoides (Levander) Langhans, (5 356 cells-mL-1) and a microcystin concentration of 1.97 μg∙L-1was found in the raw water reservoir. Samples sites were assigned the following numbers: (1) raw reservoir water; (2) WTP entry; (3) after sedimentation; (4) filtered water; and (5) treated water. Cell removal was evaluated by cell counting conducted with an inverted microscope, chlorophyll-a by a colorimetric method and microcystin by an enzyme immunoassay kit. Conventional water treatment was effective in removing chlorophyll-a, Microcystis sp. and Ceratium furcoides, mainly in the early treatment steps. Microcystin persisted until the last treatment step, when approximately 50% of the microcystin that had arrived at the WTP was removed by disinfection. Removal of these taxa and toxin was above 98%. Despite the efficacy of Ceratium furcoides removal, the presence of this dinoflagellate in treated water is considered to be large because of its large size. <![CDATA[<b>A bibliometric analysis of drinking water research in Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502016000400012&lng=pt&nrm=iso&tlng=pt A total of 1 917 publications of drinking water research in Africa from 1991 to 2013 were identified from the data hosted in online version of SCI-Expanded, Thomson Reuters Web of Science, for bibliometric analysis. The analysis included publication output, distribution of keywords, journals and subject areas, and performances of countries, institutions, and authors. Citation trends and highly-cited publications are also reported. We found that the publication output of related documents increased over the entire period of study. The results showed that 'water', 'drinking water', and 'oxidative stress' were the most frequent terms in publication titles, authors' keywords and KeyWords Plus. The top three subject areas were 'water resources', 'environmental science', and 'environmental and occupational public health'. The ten most productive institutions were located in South Africa and Egypt, and the University of Pretoria was the overall most productive institution. Thus, a quarter of all of the articles published were from South Africa. It was found that articles became increasingly collaborative with greater numbers of authors, page counts and bibliographies. More than half of the internationally collaborative articles were co-authored with researchers from Europe. French and US institutions contributed to the highest number of collaborative articles. <![CDATA[<b>Synthesis of robust flexible polyethersulfone ultrafiltration membranes supported on non-woven fabrics for separation of NOM from water</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502016000400013&lng=pt&nrm=iso&tlng=pt This work describes the synthesis of structurally robust ultrafiltration (UF) polyethersulfone (PES) membranes supported on three different types of non-woven fabrics (NWFs) prepared using a simple phase inversion method. The NWF supported membranes exhibited high mechanical strength compared to the unsupported PES membranes modified with polyvinyl pyrrolidone (PVP) due to the strength provided by the NWFs. The tensile strength of the supported PVP modified membranes was ~7 MPa compared to ~2 MPa observed for the PVP modified unsupported UF membranes. The use of the NWFs clearly provides robustness to the modified membranes. The membrane surfaces became hydrophilic with addition of PVP and the pore sizes increased with an increase in PVP concentration (scanning electron microscopy (SEM) results). The rejection of humic acid (as a model NOM compound) was 98% for PES on NWF1, while PES membranes supported on NWF2 and NWF3 gave rejections of 94% and 96%, respectively; all with good fouling resistance. This work demonstrates that the use of a NWF support allows for the modification of the surface of the membranes without compromising the overall strength of the membranes, but more importantly the ability of the membranes to reject HA while exhibiting high resistance to fouling. <![CDATA[<b>Challenges in the potable water industry due to changes in source water quality: case study of Midvaal Water Company, South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502016000400014&lng=pt&nrm=iso&tlng=pt Midvaal Water Company treats hypertrophic water abstracted from the Vaal River to supply bulk wholesome potable water to their consumers in compliance with the South African National Standard (SANS) 241:2015 for drinking water. The facility incorporates conventional and advanced treatment processes. The aims of the study were to identify how the water treatment processes of the plant have changed over time in response to the varying water quality of the Vaal River, and to consider both current and future obstacles as well as possible solutions regarding water quality and treatment. Oxidation steps such as pre-chlorination, potassium permanganate addition, pre-ozonation and intermediate ozonation have either been applied in the past or are still operational. The dissolved air flotation plant accounts for almost 70% of total chlorophyll removal and the significance of this process was confirmed during a brief maintenance shutdown during 2015. Total chlorophyll concentrations of the source water have increased extensively since 1984, while turbidity levels have remained fairly constant but with spikes at times. The facility suffers from severe taste and odour episodes during warm periods due to the presence of methylisoborneol (MIB), released by Cyanophyceae, in the Vaal River. Concentrations of > 300 ng/L MIB have been recorded, whereas the odour threshold concentration for MIB ranges from 4 ng/L to 20 ng/L. The additional application of activated carbon to alleviate taste and odour problems has to be weighed against the cost implications for consumers, the correct type to be purchased for the organic molecules to be adsorbed, the interference of natural organic matter, and the formation of additional sludge mass, as well as the intensity and duration of taste and odour events. Midvaal remains a bulk potable water supplier and therefore has to consider the socio-economic status of their consumers where water pricing is concerned. The study ultimately emphasized the intrinsic value of protecting water resources. <![CDATA[<b>Estimating runoff from ungauged catchments for reservoir water balance in the Lower Middle Zambezi Basin</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502016000400015&lng=pt&nrm=iso&tlng=pt The Lower Middle Zambezi Basin is sandwiched between three hydropower dams; Kariba, Kafue (Itezhi-tezhi) and Cahora Bassa. The operation of the upstream dams impacts on the inflows into the downstream Cahora Bassa Dam which, in turn, affects the area inundated upstream of the Cahora Bassa Dam. This study applied a rainfall-runoff model (HEC-HMS) and GIS techniques to estimate both the gauged and ungauged runoff contribution to the water balance of Cahora Bassa. The rivers considered in the study are the Zambezi, Kafue, Luangwa, Chongwe, Musengezi and Manyame. Missing data were generated using the mean value infilling method. The DEM hydro-processing technique was used to determine the spatial extent of the ungauged area. A hydrological model, HEC- HMS, was used to simulate runoff from the ungauged catchments. Results from the study show that the ungauged catchment contributes about 12% of the total estimated inflows into the Cahora Bassa Dam. Averaged results over 30 years show total inflows of 71.73 x 10(9) m³/yr, total outflows of 52.25 x 10(9) m³/ yr and a residual storage of 20 x 10(9) m³/yr. The study successfully estimated the water balance of the Middle Zambezi Basin which, in turn, may help to inform the operation of the Cahora Bassa Dam and management of artificial floods in the basin. <![CDATA[<b>Water quality modelling and optimisation of wastewater treatment network using mixed integer programming</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502016000400016&lng=pt&nrm=iso&tlng=pt Instream water quality management encompasses field monitoring and utilisation of mathematical models. These models can be coupled with optimisation techniques to determine more efficient water quality management alternatives. Among these activities, wastewater treatment plays a crucial role. In this work, a Streeter-Phelps dissolved oxygen model (DO) is implemented in a semi-hypothetical Upper Olifants River system to forecast instream dissolved oxygen profiles in response to different wastewater discharge scenarios. A mixed integer programming (MIP) numerical approach was used in the simulation and determination of the best treatment regimen to meet the instream DO standard at the minimum cost for the chosen river catchment. The Olifants River catchment modelled in this study features 9 wastewater treatment plants. Three treatment levels were evaluated for biochemical oxygen demand (BOD) and the impact was evaluated at specific measuring points (checkpoints) within the river system. Using this model, it was demonstrated that water quality standards can be met at all monitoring points at a minimum cost by simultaneously optimising treatment levels at each treatment plant. <![CDATA[<b>Estimates of the impacts of invasive alien plants on water flows in South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502016000400017&lng=pt&nrm=iso&tlng=pt The adverse impacts of alien plant invasions on water flows have been a prime motivation for South Africa's Working for Water Programme. The approach used in this study builds on a previous national assessment in 1998 by incorporating factors that limit plant water-use, information from recent research and improved flow reduction models. The total reduction in flows is estimated to be 1 444 million m³-yr-1 or 2.9% of the naturalised mean annual runoff (MAR), less than half of the 3 300 million m³-yr-1 estimated in 1998. Two main factors account for this difference: (a) a decrease in the estimated unit-area flow reduction to 970 m³-ha-1-yr-1 compared with 1 900 m³-ha-1-yr-1 estimated in 1998, largely due to the new model being based on more representative reduction factors; and (b) the updated estimate of the condensed invaded area of 1.50 million ha (previously 1.76 million ha), although the taxa mapped for this assessment only accounted for 1.00 million of the 1.76 million ha reported in 1998. Reductions due to invasions in Lesotho are estimated to be about 161 million m³-yr-1 and those in Swaziland about 193 million m³-yr-1. The taxon with the greatest estimated impact was wattles (Acacia mearnsii, A. dealbata, A. decurrens) with 34.0% of the total reductions, followed by Pinus species (19.3%) and Eucalyptus species (15.8%). The revised estimate is considered on the low side largely because the extent and impacts of riparian invasions have been underestimated. If the current estimates that 4-6% of Acacia mearnsii, Eucalyptus, Populus and Salix invasions are riparian, are adjusted to a more representative 20%, 50%, 80% and 80%, respectively, the total reductions increase by nearly 70% to ~2 444 million m³-yr-1. Producing these estimates involved a number of assumptions and extrapolations, and further research is needed to provide more robust estimates of the impacts. <![CDATA[<b>Estimating total evaporation at the field scale using the SEBS model and data infilling procedures</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502016000400018&lng=pt&nrm=iso&tlng=pt The spatial representativeness of total evaporation estimates (ET) acquired from conventional approaches is limited, as these techniques generally provide site-specific values. The use of satellite earth observation has shown a great deal of potential in capturing spatially representative hydro-meteorological flux data and therefore represents a practical alternative for estimating ET. However, one of the challenges facing ET estimation using satellite earth observation data is the effect of clouds, which reduce the number of satellite images available for use. The objectives of this paper were firstly to validate satellite-derived ET estimates against estimates acquired from a surface renewal system and, secondly, to assess the feasibility of two infilling techniques to create a daily satellite-derived ET time series. The Surface Energy Balance System (SEBS) model was used to derive daily ET using MODIS imagery. Two infilling approaches, the Kc approach and a linear interpolation approach, were evaluated by comparing their respective values against in-situ ET measurements, as well as SEBS ET estimates derived using MODIS. The results showed that SEBS ET estimates were approximately 47% higher and produced R² and RMSE values of 0.33 and 2.19 mm-d-1, respectively, compared to in-situ ET values. The ET estimates obtained by applying the Kc approach and the linear interpolation approach compared favourably with the in-situ ET values, producing RMSE values of 0.9 mm-d-1and 0.6 mm-d-1, respectively. However, comparisons of ET estimates acquired by applying the Kc act approach and the linear interpolation approach against the SEBS ET indicated a poor match, yielding RMSE values of 1.96 mm-d-1and 1.54 mm-d-1, respectively. <![CDATA[<b>Improving the understanding of rainfall distribution and characterisation in the Cathedral Peak catchments using a geo-statistical technique</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502016000400019&lng=pt&nrm=iso&tlng=pt The characterisation of rainfall variability, spatially and temporally, is essential for hydrological and ecological analyses. Inherently, this variability is distinctly more obvious in mountainous areas compared to lowlands. The objective of this study was to ascertain if the use of the regression-Kriging technique would provide improved estimates and understanding of the rainfall distribution across the Cathedral Peak catchments in the Drakensberg escarpment region, South Africa. Findings showed longitude and altitude to be the overall best predictors of the distribution of rainfall for the annual period, wet season and dry season, with longitude explaining 72% and altitude explaining 26% of the rainfall variability for mean annual precipitation, 73% and 26% for the wet season and 50% and 22% for the dry season, respectively. The combination of both longitude and altitude showed a larger coefficient of determination, of 0.73, 0.74 and 0.51, for the annual, wet season and dry season, respectively. Long-term mean annual rainfall patterns showed an overall strong directional distribution from west to east with a distinct pattern observed during the dry season. It was concluded that regression-Kriging is a useful alternative method for characterising rainfall distribution as well as prediction errors for mountainous areas. <![CDATA[<b>Horizontal variation in trace elements and soil characteristics at Siloam and Tshipise geothermal springs, Limpopo Province, South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502016000400020&lng=pt&nrm=iso&tlng=pt The Limpopo Province is the location of 31% of South Africa's geothermal springs. The springs at Siloam and Tshipise are among those springs which fall into the 'scalding category' with average temperatures of 67.7°C and 54.6°C, respectively. The aim of this study was to determine the horizontal variation in trace element concentrations and soil indicators in surface soil associated with the geothermal springs at Siloam and Tshipise. Results show that, in general, the trace element concentrations present in the soil decrease with horizontal distance from the springs. Water and soil samples were collected from May to July 2014, with the soil sampled at 0-15 cm depth at 5 m intervals in the horizontal distance from the geothermal spring. The physicochemical parameters of the water were determined as well as the trace elements. The soil samples were digested using microwave digestion and trace elements were determined using an inductively coupled plasma-mass spectrometer (ICP-MS). Soil indicators - pH, soil organic matter (SOM) and soil water retention (SWR) - were also determined. The resulting data were subjected to both descriptive and factor analyses. Results showed only one factor determining the variation in geothermal water, attributed to the rock-water interaction in the deep aquifer (geology); two factors were obtained for variation in soil indicators and trace element concentrations, attributed to spring geology and the soil pedogenesis. There was a strong correlation between the trace elements and soil indicators at the 95% confidence level. There is generally a positive correlation between the trace elements and soil indicators if the soil pH, SOM and SWR are high; in these instances most of the trace elements in the soil will also be relatively high. A two-factors-without-replication ANOVA (p < 0.05) showed that there is a significant difference in trace element concentrations at different distances. <![CDATA[<b>A critical look at South Africa's Green Drop Programme</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502016000400021&lng=pt&nrm=iso&tlng=pt In this paper we briefly reflect on the different legislation and types of regulatory mechanisms that South Africa's Department of Water and Sanitation (DWS) has in place to try to improve the performance and compliance of water services authorities (WSAs) in the controversial wastewater services sector. In particular, we focus on DWS's incentive-based mechanism, the National Green Drop Certification Programme (Green Drop Programme), and evaluate the achievements and challenges associated with its implementation to date. While there has been considerable improvement in performance in all areas of the programme since its inception in 2009, much still needs to be done in order to address the dire situation the country's wastewater services sector finds itself in. Challenges facing the Green Drop Programme and the municipalities implementing the programme include: lack of human resource capacity to prepare effective corrective action plans and/or wastewater risk abatement plans; lack of finances for mainstreaming of wastewater treatment in municipal decision-making; lack of forward planning; problematic bureaucratic processes; complex relationship between some municipalities and DWS; theft, vandalism and misuse of wastewater treatment infrastructure and not enough transparency. Based on this discussion, we make some concluding remarks about possible areas of improvement that could potentially strengthen the functioning and success of this programme, and thereby help to improve the levels of performance and compliance of the country's WSAs.