Scielo RSS <![CDATA[Water SA]]> vol. 44 num. 3 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>Prediction of wind drift and evaporation losses of a sprinkler irrigation system using principal component analysis and artificial neural network technique</b>]]> Principal component analysis was merged with the artificial neural network (ANN) technique to predict wind drift and evaporation losses (WDEL) from a sprinkler irrigation system. For this purpose, field experiments were conducted to determine WDEL under different conditions. Data from field experiments and previous studies were used as sample data to train the ANN model. Three models were developed to predict WDEL. In the first model (ANN1), 9 neurons (riser height, main nozzle diameter, auxiliary nozzle diameter, discharge rate of the main nozzle, discharge rate of the auxiliary nozzle, operating pressure, wind speed, air temperature and relative humidity) were used as the input layer. In the second model (ANN2), 7 neurons (riser height, operating pressure, wind speed, air temperature and relative humidity, diameter ratio and discharge ratio) were used as the input layer. The third model (ANN3) used a multivariate technique (PC1, PC2, and PC3). Results revealed that the ANN3 model had the highest coefficient of determination (R² = 0.8349). The R² values for the ANN1 and ANN2 models were 0.7792 and 0.4807, respectively. It can be concluded that the ANN3 model has the highest predictive capacity. <![CDATA[<b>Using network analysis to analyse the complex interaction of factors causing the failure of small-scale water infrastructure (SWI) in the rural areas of South Africa</b>]]> Some parts of the rural areas of South Africa are receiving water services below the legislative standards stipulated in the Water Services Act (1997) of South Africa. This is because small-scale water infrastructures (SWI), including standpipes, handpumps and windmills, are failing to supply adequate water in rural communities for various activities that enhance their livelihoods. This is due to technical, community, institutional, and environmental factors. Literature indicates that these factors are complex in nature. However, research on their complex interactions has been limited. Therefore, the complex interactions of the factors causing SWI failure were investigated and analysed in this study. A qualitative research approach was employed to investigate the factors that cause failure of SWI. The network approach combined with graph theory and the community structure method were used to generate a theme and domain network that allowed for a systematic analysis and interpretation of the causes of SWI failure in the study area. The major causes of failure identified include: (i) the use of a top-down approach to implement water projects in rural communities without consultation, (ii) sharing of SWI in high numbers due to the limited number of SWI available/functional, resulting in overloading and increased breakdowns, and (iii) drying up of water sources due to poor siting leading to vandalism of SWI. Overall, the causes of SWI failure are as a result of the complex interactions of different categories of factors. The theme and domain network is a powerful tool that can be used represent and analyse the complex interactions. It is therefore imperative for interventions aiming to improve rural water supply to analyse the complex interactions of the causes of SWI failure to understand the underlying problems at a level of a system, in order to propose suitable solutions. <![CDATA[<b>Water research and collaboration in the Southern African Development Community</b>]]> This article investigates water-related research in the Southern African Development Community. Water issues are part of the region's science and technology priorities as 4countries receive less rain than the global average of 860 mm/yr - Botswana with 400 mm/yr, Namibia with 254 mm/yr, South Africa with 497 mm/yr and Zimbabwe with 652 mm/yr. Furthermore, the international literature indicates that joint or internationally coordinated research has the potential to improve the scientific-technical quality of international agreements, prevent conflict and shape the way for appropriate management of the shared resources. Scientometric analysis using the Web of Science database is employed in order to identify the state of water research and collaboration in the SADC region. The Web of Science indexes a defined set of journals worldwide and the South African Government provides incentives/subsidies for publications indexed by this database. The results show that South Africa is the main producer (80%) of research publications in the region. Similarly, in the field of water research South Africa produces 75% of the region's research. The SADC collaboration matrix in water-related research reveals that there is minimal, if any, collaborative research on the topic. Some seed-level research exists between South Africa, Zimbabwe and Namibia. The main funders of research are the South African National Research Foundation (NRF) (acknowledged in 180 publications), the Bill & Melinda Gates Foundation (72 publications), the National Institutes of Health (64 publications) and the Wellcome Trust (60 publications). Policy implications are discussed (e.g. the establishment of SADC Common Water Research Area; research support for the region, etc.). <![CDATA[<b>Assessing the performance and robustness of the UNICEF model for groundwater exploration in Ethiopia through application of the analytic hierarchy process, logistic regression and artificial neural networks</b>]]> This study assesses the performance and robustness of the groundwater potential (GWP) maps produced by the UNICEF model for deep groundwater exploration in Ethiopia. The UNICEF model is a weighted linear combination of hydrogeological parameters including permeability, slope, recharge, and lineament density, which has been calibrated using the expert judgements of local hydrogeologists. In order to assess the performance and robustness of the model, three techniques were employed: the analytic hierarchy process (AHP), logistic regression (LR), and artificial neural networks (ANNs). Three study areas (Dallol, Halaba and Shinelle) were selected on the basis of climatic and geological variation, in addition to the availability of well data pertaining to depth and yield. The performance of the UNICEF model in predicting outcomes of the well data included in the study was assessed by computing the receiver operating characteristic (ROC) curve. The solutions produced by the AHP and ANN were more accurate than the UNICEF model in determining the productivity of deep wells in the study data, whilst the LR model was less accurate than the UNICEF model. The groundwater productivity maps produced by the AHP and ANNs showed clear correlation with the maps produced by the UNICEF model, despite moderate (AHP) and severe (ANN) parameter perturbation, demonstrating the robustness of the UNICEF model. Whilst the AHP and ANN models demonstrated higher accuracy than the UNICEF model, this must be considered against the well data used to assess accuracy, which were drawn from a small sample of non-ideal distribution. Although this study focuses on case studies in Ethiopia the key findings are applicable internationally, namely, that the use of the AHP in data-scarce environments provides robust models, and that with the addition of easily obtainable well data the accuracy of modelling can be significantly increased through the application of ANNs. <![CDATA[<b>Electrospun chitosan-based nanofibres for removal of phenols from drinking water</b>]]> Chitosan-based nanofibres were synthesized using a fibre electrospinning technique and tested for the removal of 3-methyl-4-nitrophenol from aqueous solutions. The downside of chitosan-based materials is swelling. In this study, it was found that the addition of polyisoprene not only improved the electrospinning ability of chitosan but also reduced the swelling of the nanofibres by 50%. The adsorption studies of 3-methyl-4-nitrophenol on the chitosan-based nanofibres were conducted in a batch process. The nanofibres were found to remove up to 90% of 3-methyl-4-nitrophenol with an adsorption reduction capacity of 12% at each cycle of reusability test. The reduction capacity was associated with the chemical interaction of the adsorbate and the adsorbent. This indicated that the nanofibres can effectively remove 3-methyl-4-nitrophenol from water for at least 3 cycles. The adsorption efficiency improved as the degree of cross-linking was reduced and the adsorption mechanism followed the Freundlich isotherm suggesting that the adsorption of 3-methyl-4-nitrophenol occurred in different layers on the surface of the nanofibres. The degree of crosslinking of the electrospun nanofibres with glutaraldehyde was found to affect the adsorption capacity. Nanofibres with different degrees of crosslinking were used to study the effect of pH, adsorbent dose, and initial concentration. <![CDATA[<b>Assessing the performance of regional flood frequency analysis methods in South Africa</b>]]> In engineering and flood hydrology, the estimation of a design flood associates the magnitude of a flood with a level of exceedance, or return period, for a given site. The use of a regional flood frequency analysis (RFFA) approach improves the accuracy and reliability of estimates of design floods. However, no RFFA method is currently widely used in South Africa, despite a number of RFFA studies having been undertaken in Africa and which include South Africa in their study areas. Hence, the performance of the current RFFA approaches needs to be assessed in order to determine the best approaches to use and to determine if a new RFFA approach needs to be developed for use in South Africa. Through a review of the relevant literature it was found that the Meigh et al. (1997) method, the Mkhandi et al. (2000) method, the Görgens (2007) Joint Peak-Volume (JPV) method and the Haile (2011) method are available for application in a nationwide study. The results of the study show that the Haile method generally performs better than the other RFFA methods; however, it also consistently under-estimates design floods. Due to the poor overall performance of the RFFA methods assessed, it is recommended that a new RFFA method be developed for application in design flood practice in South Africa. <![CDATA[<b>Optimization of sequencing batch reactor for wastewater treatment using chemically enhanced primary treatment as a pre-treatment</b>]]> The sequencing batch reactor (SBR) is a wastewater treatment option feasible for low flows. The objective of this research was to optimize SBR by varying its operational parameters, viz. (i) settling time and (ii) reaction time. The study was conducted in two phases. In Phase 1, raw wastewater was fed into the SBR after conventional settling, while in Phase 2 raw wastewater was fed into the SBR after coagulation-flocculation-sedimentation. A bench-scale model was set up and domestic wastewater was used for this study. Performance of the treatment system was evaluated through 5-day biochemical oxygen demand (BOD), chemical oxygen demand (COD) and total suspended solids (TSS). The results demonstrated that reaction time was reduced to 4 h in Phase 2 compared to 10 h in Phase 1. The BOD, COD and TSS removal efficiencies observed in Phase 1 were 80%, 80% and 73%, respectively, and for Phase 2 the removal efficiencies were 74%, 75% and 80% respectively. National Environmental Quality Standards (NEQS) were met in both cases and the treatment cost per cubic metre of wastewater for Phase 2 was 2.5 times lower compared to Phase 1. <![CDATA[<b>Application of molecularly imprinted polymer designed for the selective extraction of ketoprofen from wastewater</b>]]> A molecularly imprinted polymer (MIP) that is selective to ketoprofen was synthesized and applied in the adsorption of the target compound from water. The MIP was synthesized using a bulk polymerization method at high temperatures (60-80°C), where ketoprofen, 2-vinylpyridine, ethylene glycol dimethacrylate, toluene and 1,1´-azobis(cyclohexanecarbonitrile) were used as template, functional monomer, cross-linker, porogen and initiator, respectively. Non-imprinted polymer (NIP) was synthesized similarly to the MIP but in the absence of ketoprofen. From molecular dynamics simulation, the nature of interactions that occurred between the template and the functional monomer were found to be based on hydrogen bonding. This was confirmed experimentally, where a high extraction efficiency of ≥ 90% was obtained at acidic conditions (pH 5) due to the protonation of ketoprofen. A contact time of 45 min was sufficient for the maximum adsorption of ketoprofen from 10 mL spiked water using 8 mg of the adsorbent. MIP showed greater selectivity than NIP by achieving a relative selectivity coefficient of 7.7 towards ketoprofen in the presence of structurally related pharmaceuticals. Furthermore, the order of sorption onto the MIPs from water was ketoprofen > fenoprofen > gemfibrozil. From a modelling perspective, the Langmuir adsorption isotherm and pseudo-second-order kinetic model gave the best fit, with maximum adsorption capacity of 8.24 mg·g−¹ and sorption rate constant of 0.25 mg·g−¹·min−¹ for MIP. This was translated to chemisorption of ketoprofen onto the homogeneous MIP binding sites. This work demonstrated the great potential of MIP in selective recognition of ketoprofen from wastewater relative to closely related compounds. <![CDATA[<b>Impact of variable speed pumps on water quality in distribution systems</b>]]> Water quality has become a prominent issue in the study of water distribution networks. Variable speed pumps (VSPs) can control and improve the performance of water distribution systems. However, they may have effects on the water quality. The objective of this study was to investigate the impact of VSPs on water quality. The EPANET water quality simulator was applied for modelling water age and chlorine residual in a distribution network. In addition, intrusion of an active contaminant and analysis of leakage effects on residual chlorine concentration were performed through extended period simulations. Results indicate that VSPs may have negative impacts on water quality, including increased water age during low consumption times, and reduced disinfectant residuals at peak hours. In addition, the average rate of chlorine decay for fixed speed pumps (57%) is higher than that for VSPs (54%) when a conservative contaminant (sewage water) is considered. <![CDATA[<b>Predicting continuous form of soil-water characteristics curve from limited particle size distribution data</b>]]> Detailed information derived from a soil moisture characteristics curve (SMC) helps in water flow and solute transport management. Hence, prediction of the SMC from soil particle size distribution (PSD), which is easy to measure, would be convenient. In this study, we combine an integrated robust PSD-based model and a Van Genuchten SMC model to predict a continuous form of SMC using sand, silt and clay percentages for 50 soils selected from the UNSODA database. We compare the performance of the proposed approach with some previous prediction models. The results indicated that the SMC can be predicted and modelled properly by using sand, silt, clay and bulk density data. The model's bias was attributed to the high fine particle and organic carbon (OC) content. We concluded that independence of the proposed method from the database and any empirical coefficients make predictions more reliable and applicable for large-scale water and solute transport management. <![CDATA[<b>Multiple criteria decision analysis for sanitation selection in South African municipalities</b>]]> A multiple criteria decision analysis (MCDA) was developed for the selection of sanitation systems. This decision support system was aimed at assisting municipal engineers to design and implement sustainable solutions to meet a municipality's obligation to provide free basic sanitation (FBS). Multi-attribute value theory (MAVT) was selected as the method most suited to the problem under consideration. Criteria which determine the sustainability of sanitation were selected from the literature and a spreadsheet-based MCDA with stakeholder and expert user interfaces was developed. Stakeholders determine the weighting of each indicator and expert users determine the values to be entered for the alternatives against each indicator. The partial values are aggregated using a weighted sum function. Research carried out into the implementation of FBS by the eThekwini Municipality that includes the city of Durban was analysed. This informed the allocation of indicator values to the sanitation alternatives under consideration: ventilated improved pit latrines (VIPs) and urine diversion dehydrating toilets (UDDTs). An innovative scenario analysis method was used to determine the effect of different weightings and/or values, representing changes in stakeholder involvement, resource recovery and political support for ecological sanitation. The MCDA was found to provide a guiding framework for municipal engineers in their efforts to implement sustainable sanitation. The process of deriving values for the MCDA is likely to prove even more useful than the overall value scores of the options under consideration. <![CDATA[<b>Penetrometer tests on 109 pit latrines in Kibera, Nairobi, Kenya</b>]]> Pit latrine contents can have varying consistencies that make the pits challenging to empty. It has been assumed that solids sink to the bottom of the pit with a more liquid layer above this and a scum on the top. This implies that it would be possible to remove the uppermost layers with a pump. However, recent studies have found alternative sludge profiles, including a thick crust on the top. This paper presents penetrometer data from a large number (109) of pit latrines in Kibera, Nairobi, Kenya. The penetrometer consists of a weight, dropped onto an anvil that drives a cone into the pit. The depth of penetration following each impact was measured. This was converted into plots of depth in the pits against penetration. Each pit was analysed using Spearman's rank correlation coefficient, and categorised into positive or negative correlation, significant or non-significant. Significant, negative correlation was assumed to correspond to pits where the solids had sunk to the bottom. 38% of pits were classified in this way, which suggested that while it is common that the number of impacts required to penetrate the sludge increases with depth in the pit, this is not always the case. Pit emptiers should be prepared to deal with pits with a variety of sludge profiles, including those with a solids layer at the top. <![CDATA[<b>Economic risks due to declining water quality in the Breede River catchment</b>]]> Water is a critical resource necessary to support social and economic development. Economic growth and, in particular, the growth of urban and peri-urban areas, however results in declining water quality which threatens water-dependent industries. In developing countries this is a particular concern due to the rapid rate of urbanisation and the limited financial resources and technical capabilities to adequately maintain and upgrade wastewater treatment works. This is particularly relevant in catchments with a high dependence on export-orientated agriculture. This study considered water quality risks in the Breede River catchment as an area which experiences significant urban and peri-urban growth, focusing on economic risks associated with declining water quality, estimates of the costs needed to rehabilitate existing wastewater treatment works, and alternative strategies such as the use of artificial wetlands, the rehabilitation and protection of natural wetlands, as well as the clearing of invasive alien plants. A major conclusion is that the financial risk associated with a declining economy and social instability outweighs the costs that will be needed for rehabilitation of existing treatment plants. Together with more pronounced fluctuations in precipitation anticipated with climate change, these risks due to declining water quality are likely to increase in future with continued urban and peri-urban growth. <![CDATA[<b>Exploring ways to increase public investments in agricultural water management and irrigation for improved agricultural productivity in Southern Africa</b>]]> This paper explores ways to increase public investments in agricultural water management and irrigation for improved agricultural productivity in Southern Africa, with a specific focus on Malawi, Mozambique and Zambia. The analysis was based on a critical review of literature and assessment of the national agricultural investment plans and agricultural/water policies in the study countries. Despite the potential to improve agricultural productivity, irrigation does not currently play a significant role in Southern African agriculture. There have been efforts and formal commitments at the continental, regional and country levels to promote investments in agricultural water management and irrigation to improve and sustain agricultural productivity. However, despite these commitments, actual implementation has been a challenge and the first 5 years of national agricultural investment plans have passed or are now coming to an end without much progress having been made regarding actual investments. Lack of adequate resources and institutional capacity have been some of the challenges affecting implementation of the investment plans to meet commitments in sustainable land and water management. Overall, as countries plan for the second phase of the CAADP programme, there are opportunities to ensure that investments in agricultural water management and irrigation and complementary technologies are prioritised and allocated adequate resources for implementation. <![CDATA[<b>Measuring and modelling evapotranspiration in a South African grassland: Comparison of two improved Penman-Monteith formulations</b>]]> Accurately measuring evapotranspiration (ET) is important in the context of global atmospheric changes and for use with climate models. Direct ET measurement is costly to apply widely and local calibration and validation of ET models developed elsewhere improves confidence in ET derived from such models. This study sought to compare the performance of the Penman-Monteith-Leuning (PML) and Penman-Monteith-Palmer (PMP) ET models, over mesic grasslands in two study sites in South Africa. The study used routine meteorological data from a scientific-grade automatic weather station (AWS) to apply the PML and PMP models. The PML model was calibrated at one site and validated in both sites. On the other hand, the PMP model does not require calibration and hence it was validated in both sites. The models were validated using ET derived from a large aperture scintillometer (LAS). The PML model performed well at both sites with root mean square error (RMSE) within 20% of the mean daily observed ET (R² of 0.83 to 0.91). Routine meteorological data were able to reproduce fluxes calculated using micrometeorological techniques and this increased the confidence in the use of data from sparsely distributed AWSs to derive reasonable ET values. The PML model was better able to simulate observed ET compared to the PMP model, since the former models both transpiration and soil evaporation (E S), while the latter only models transpiration. Hence, the PMP model systematically underestimated ET in a context where the leaf area index (LAI) was < 2.5. Model predictions in the grasslands could be improved by incorporating the E S component in the PMP model while the PML model could be improved by careful choice of the number of days to be used in the determination of the fraction of E S. <![CDATA[<b>Effects of different mulch types on soil moisture content in potted shrubs</b>]]> South Africa is classified as a semi-arid environment with limited natural water resources and variable rainfall. It is also described as water scarce, with many of its water resources already fully exploited. Gardening is one of the principal methods that people use to experience nature, and gardens can also be a public demonstration of personal value, a source of satisfaction, and part of a connection to the community. However, gardens are also one of the top users of water, accounting for approximately 31-50% of potable water supplied for domestic and urban use. In order to reduce the amount of water used in gardens, water conservation strategies such as mulching need to be employed. In view of South Africa's water situation, it is Rand Water's aim to promote the wise use of water, in all aspects of water consumption. It is anticipated that this study will provide information useful to water saving in urban gardens and landscapes, and will promote the use of mulch amongst gardeners, landscapers and the general public. Mulching potted plants with various organic and inorganic mulch was found to conserve an average of 35% more soil water content over approximately 6 weeks of no irrigation than plants with no mulch. Mulch was shown to increase plant health and vitality, as indicated by stomatal conductance, by an average of 44% than plants with no mulch. The recommended mulch type for use in gardens is bark chips in both summer and winter seasons. <![CDATA[<b>A tool for determining maximum sustained swimming ability of selected inland fish species in an Afrotropic ecozone</b>]]> Critical swimming speed (Ucrit) predicts the maximum sustained swimming velocity that various fish species are able to sustain for prolonged periods. The objective of this study was to determine the Ucrit of Afrotropic ecozone fish, determine oxygen consumption at Ucrit and relate the resulting optimum flow requirements to effective movement through fishways under South African flow conditions. The selected fish species were Coptodon rendalli, Tilapia sparrmanii, Pseudocrenilabrus philander, Oreochromis mossambicus and Enteromius trimaculatus. Ucrit and oxygen consumption (MO2) were measured in a swim respirometer at 5-min intervals, at increasing velocity increments of 0.5 cm·s−¹ until volitional exhaustion. No significant differences were seen in the Ucrit values between C. rendalli, T. sparrmanii and P. philander, but all species significantly differed from O. mossambicus and E. trimaculatus, which had the highest Ucrit (17.6 ± 1.5 bl·s−¹ and 18.2 ± 2.8 bl·s−¹). Size plays an important role in the swimming performance of fish, with larger fish able to sustain a greater velocity, which was specifically true for O. mossambicus in this study. Additionally, smaller fish consumed more oxygen during swimming and therefore used more energy, experiencing relative physiological strain. Based on these data, flow respirometry was shown to be a useful tool to determining prolonged swimming abilities of South African fish species, and can help inform the structure and flow rates of culverts and fishways. <![CDATA[<b>Challenges and opportunities for revitalising smallholder irrigation schemes in South Africa</b>]]> South Africa is classified as a water-scarce country, and depends on agriculture for food production. The irrigation sector is the largest consumer of water in the country, accounting for about 62% of water utilisation, but also losing 30-40%. Given the threat of drought and climate change, efficient irrigation systems have become a necessity, especially in the smallholder farming sector where most losses occur. Smallholder irrigation schemes (SIS) were developed to improve rural livelihoods through sustainable food production for food security and poverty alleviation, but these development objectives remain largely unfulfilled. The objectives of this review were to assess challenges facing SIS and explore opportunities for revitalising the schemes. The focus was on government policy and strategies to support smallholder farmers. A review of government policy showed that although the needs and interests of smallholder farmers are high on the national agenda, there is insufficient financial support to the sector, suggesting that smallholder agriculture is not really seen as a potential driver of the economy. The core focus of the government on repairing irrigation infrastructure while neglecting the soft components relating to capacity building has partly been blamed for the failure of SIS in South Africa. Capacity building is one of the missing links in smallholder irrigation development and many failures have been attributed to lack of adequately trained farmers and extension staff, particularly in irrigation water management. Land tenure insecurity has been singled out as a major institutional challenge leading to poor performance of irrigation schemes. The diversity of schemes means that different kinds of interventions are needed to respond to varying farmers' needs, resources and agricultural contexts. These findings point to the need to balance the soft and hard components of the irrigation schemes for sustainability. It is therefore evident that the government needs to review its priorities in revitalisation of SIS. Land tenure policies allowing increased access to arable land need to be developed urgently, together with the promotion of alternative cropping systems that are suitable for the smallholder farming sector. <![CDATA[<b>Nutrient removal and microbial settlement in a full-scale subsurface wastewater infiltration system: Impact of varying hydraulic and organic loads and temperature</b>]]> A series of experiments was conducted through a full-scale subsurface wastewater infiltration system (SWIS) to investigate the impact of hydraulic loading rate (HLR), organic loading rate (OLR) and underground temperature on nutrient removal and microbial settlement. Taking the hydraulic and treatment performance into consideration, HLR of 0.10 m³/(m²·d) was recommended with average NH3-N, TN, COD and TP removal rates of 82.6%, 81.5%, 80.9% and 90.9%, respectively. Considering treatment performance, OLR of 10.4 g BOD/(m²·d) was recommended with average NH3-N, TN, COD and TP removal rates of 88.1%, 84.8%, 86.3% and 91.3%, respectively. The number of nitrifying bacteria in each layer in the matrix decreased with increasing HLR, and the number of denitrifying bacteria increased with increasing HLR, at 0.8 and 1.0 m depths. When OLR increased, the number of bacteria and denitrifying bacteria at 0.8 and 1.0 m depths increased, and the number of nitrifying bacteria decreased. Average NH3-N, TN and COD removal rates increased with underground temperature increasing. The number of bacteria, nitrifying bacteria at 0.4 and 0.6 m depths and denitrifying bacteria at 0.8 and 1.0 m depths, increased with underground temperature increasing.