Scielo RSS <![CDATA[Water SA]]> vol. 48 num. 2 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>Flood frequency analysis - Part 1: Review of the statistical approach in South Africa</b>]]> Statistical flood frequency analyses of observed flow data are applied to develop regional empirical and deterministic design flood estimation methods, particularly for application in cases where no, or insufficient, streamflow data are available. The soundness of the statistical approach, in the estimation of flood peak frequencies, depends on the availability of long records with good-quality observed flow data. With flood frequency methods currently under review in South Africa, a sound statistical approach is considered essential. This paper reviews the statistical flood frequency approach in South Africa, which includes an appraisal of the capability of the most commonly used probability distributions in South Africa to properly cope with the challenges encountered in a flood frequency analysis, based on extended experience in flood hydrology. All the distributions tend to perform poorly when lower probability frequency events are estimated, especially where outliers are present in the dataset. Research needs are identified to improve flood peak frequency estimation techniques, and practical pointers are suggested for the interim, in anticipation of updated methods. The importance of a visual interpretation of the data is highlighted to minimise the risk of not selecting the most appropriate distribution. <![CDATA[<b>Flood frequency analysis - Part 2: Development of a modified plotting position</b>]]> The original plotting position concept was suggested more than a century ago. Since then, many alternative plotting position approaches have been developed. Despite a general lack of agreement around which plotting position is theoretically 'correct' and the 'best' to use, all plotting positions fail to adequately address outliers and data of similar magnitude. Hydrologists generally fail to acknowledge that the plotting position primarily offers an informative display of data, against which distributions can be compared, rather than an absolute measure of probability. This paper does not intend to challenge any of the many lengthy theoretical mathematical arguments, utilised to 'prove' why one plotting position is superior to the others. These theoretical arguments may very well be valid for a 'population' of flood peaks - the reality, however, is that hydrologists are confronted with the challenge of analysing very limited 'samples' of the population. Consequently, the plotting position issue demands a more pragmatic approach, rather than a purely theoretical approach. This paper illustrates various problems with existing plotting position techniques in use and offers an alternative approach and a more sensible plotting position technique, using Z-scores and referred to as the Z-set PP, against which distributions can be checked. The study further illustrates how effectively the Z-set PP deals with outliers and its robustness with various record lengths. Although derived from a study of flood peak data obtained from South African flow-gauging sites, it is deemed that it will be universally applicable. <![CDATA[<b>The impacts of long-term flow reductions and an extreme drought on a large, permanently open estuary, and implications for setting the ecological reserve</b>]]> Environmental water requirements (EWRs) are set for South Africa's estuaries to ensure that they are maintained in a state that is both achievable and commensurate with their level of conservation and economic importance. However, these EWRs are typically determined on the basis of models and scenario analyses that require extrapolation beyond existing data and experience, especially if climate change is considered. In the case of the Berg Estuary, South Africa, available data on changes in freshwater flow and water quality span a period of at least five decades (1970s-present) during which significant reduction in flows has been observed. Monitoring data also cover an extreme 3-year drought, from 2015-2017, which provided a unique opportunity to study the effects of severe freshwater starvation (zero-flow for an extended period) on this large, permanently open system. Our analyses show that mean annual runoff (MAR) under present-day conditions has been reduced to around 50% of that under reference (natural) conditions and that reduction in runoff during the low-flow season (summer) has been more severe (80-86% reduction) than for the high-flow season (39-42% reduction). The salinity gradient now extends much further upstream than under reference conditions. Hypersaline conditions along with a reverse salinity gradient were recorded in the estuary for the first time ever during the drought of 2015/17. Levels of dissolved inorganic nitrogen (NOx) reaching the estuary from the catchment have increased dramatically (6-7 fold) over the past five decades, dissolved reactive phosphate (PO4) slightly less so (2-3 fold), but ammonia (NH4) hardly at all. Increases in nutrient input from the catchment in the high-flow season are also much more dramatic than in the low-flow season. The estuary is no longer compliant with gazetted EWRs and requires urgent interventions to restore the quantity and quality of freshwater it receives. <![CDATA[<b>Utility of geospatial techniques in estimating dam water levels: insights from the Katrivier Dam</b>]]> To achieve informed integrated water resource management and sustainability, an understanding of the quantity of water available for use within a spatial and temporal context is needed. This study was consequently focused on the estimation of water levels with the use of geospatial techniques. The availability of water data is a significant challenge, especially for smaller dams used by farmers. The lack of consistent water data in turn poses a problem by limiting the estimation of the overall water availability in water strategy models. This challenge is attributed to the cost of modeling all available water resources and the lack of complete records of all available water resources, as some small dams are not officially registered. This paper provides a simple protocol that can be implemented to reliably derive water levels for dams that are yet to be registered or accounted for, using the Katrivier Dam as a case study. Three main datasets were used which enabled the calculation of water levels - a 12.5 m digital elevation model, Sentinel-2 optical images, and water data from the Department of Water and Sanitation (DWS), as in-situ data. The resulting water level values were derived using a proposed model that includes two correction factors, k and s. The results obtained showed that the estimated water levels from the model proposed in this paper are analogous with those observed by the DWS. Therefore, the proposed method can serve as an additional cost-effective method in water accounting procedures as it requires less expensive equipment than alternatives such as bathymetric methods. <![CDATA[<b>Estimating sanitary sewer pipeline infrastructure from basic characteristics of a service zone</b>]]> The standard design and cost estimation for a sewer network involves considerable time and financial investment. There are, however, many cases where a rapid assessment of the sewer infrastructure or related costs associated with a service zone might be required. Although there are numerous approaches to rapid sewer infrastructure estimation in the literature, to date, no widely available tool has been developed that can be applied to reliably estimate the expected sewer pipeline infrastructure associated with a service zone in South Africa. The aim of this study was to develop a method for estimating the sewer pipeline infrastructure required for a service zone, based on limited information, that could be applied to future developments. A database of South African sewer network data was used in the development of three major study outcomes. Study Outcome I involved developing regression models for estimating the total sewer pipeline length using only basic service zone characteristics. Models were developed for different categories of land use and area size, allowing for estimation of the total pipeline length as a function of the service zone area size, relief, and the density of contributing users. Study Outcome II involved determining the average pipeline diameter distributions for different types of service zones, enabling disaggregation of the total pipeline length into lengths per diameter. Study Outcome III involved determining the average number of manholes per kilometre of sewer pipeline. Combined, the three study outcomes form an infrastructure estimation tool that enables the sewer pipeline length per approximate diameter and the number of manholes associated with a service zone to be estimated, applicable to service zones smaller than 450 hectares. This study illustrates how the same methodology can be followed to develop similar tools which are applicable to other specific regions or development types, provided an appropriate dataset is obtainable. <![CDATA[<b>Per capita water consumption for benchmarked South African service levels derived by means of explicit reasoning</b>]]> Per capita water use is commonly employed in single-parameter models to estimate water demand, especially in regions where model input parameters are limited. Research has confirmed that the serviced population and household size positively correlate with water consumption, but the per capita consumption of household members decreases with increased household size. A central issue driving this study was the lack of an up-to-date per capita household water use guideline in the South African context. This study followed a process of explicit reasoning and inference, informed by an extensive knowledge review, stakeholder input and interrogation of relevant data, to develop a novel per capita water use estimation tool. Five main parameters were included, namely: (i) level of water service provided, (ii) usage scenario, (iii) household size (people per household), (iv) geographic region, and (v) regional property value. A Microsoft Excel-based tool was developed and is supplied online as supplementary material with this publication. The litres per capita per day tool (LCD-tool) allows for robust per capita water use estimates, as a function of the above five input parameters. The Microsoft Excel LCD-tool provides benchmarks for different South African conditions, described by context-specific service levels. The planning and management of water supply and distribution systems could benefit from the findings of this study. <![CDATA[<b>Endotoxin removal efficiency in conventional drinking water treatment plants, a case study in Egypt</b>]]> The present study determines the endotoxin removal efficiency of drinking water treatment plants (DWTPs) in Egypt, as examples of conventional treatment methods used in developing countries. The total endotoxin in source water (Nile River) of these DWTPs ranged from 57 to 187 EU-mL-1, depending on the location of treatment plants. Coagulation/flocculation/sedimentation (C/F/S) after chlorine pre-oxidation removed bound endotoxins by 76.1-85.5%, but caused cell lysis and increased free endotoxins by 28.2-33.3% of those detected in raw waters. Rapid sand filtration had not significant effect on free endotoxins, but reduced bound endotoxins by 23-33.3%. Final chlorine disinfection also reduced bound endotoxins to levels around 1 EU/mL, accompanied by an increase in free endotoxins (37-112 EU-mL-1) in finished waters. Simultaneously, final chlorine disinfection removed all heterotrophic bacteria, with low cyanobacterial cell numbers (348-2 450 cells-mL-1) detected in finished waters. Overall, conventional treatment processes at these DWTPs could removal substantial amounts of bound endotoxins and bacterial cells, but increase free endotoxins through cell lysis induced by pre-oxidation and final chlorine disinfection. The study suggests that conventional processes at DWTPs should be optimized and upgraded to improve their performance in endotoxin removal and ensure safe distribution of treated water to consumers. <![CDATA[<b>Adsorption and desorption studies of <i>Caricapapaya </i>stem activated with zinc chloride for mining wastewater treatment</b>]]> The adsorption of eight selected potentially toxic metal ions from actual mining wastewater obtained from Igbeti, Nigeria, was established using activated carbon chemically prepared from Carica papaya stem with zinc chloride (CPSAC-ZnCl2) as activating agent. Characterization of the prepared CPSAC-ZnCl2 sample for surface morphology and functional groups was done by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy, respectively. An atomic absorption spectrophotometer (AAS) was utilized for characterization of the selected metals in the mining wastewater. Batch adsorption and desorption studies were conducted on removal of the metals from the sample using CPSAC-ZnCl2. The data obtained were fitted to isotherm (Freundlich and Langmuir); kinetic (pseudo-second-order and intra-particle diffusion) and thermodynamic (standard enthalpy change - ΔH°, entropy change - ΔS° and free energy change - ΔG°) models. These were considered under two error functions (sum of absolute errors - SAE, coefficient of determination - R²) of linear and non-linear regression analyses. The SEM micrograph revealed that the CPSAC-ZnCl2 sample was 2.0-50.0 nm with FTIR spectra absorption peaks ranging from 746.2 to 3 987.0 cm-1. The initial concentrations of selected metals in the wastewater varied from 5.7 to 756.5 mg/L. The adsorbent dosage, agitation rate, contact time, pH and temperature for optimum condition of CPSAC-ZnCl2 were 0.6 g, 150.0 r/min, 60 min, pH of 7.0 and 30°C, respectively. The selected metals' adsorption onto CPSAC-ZnCl2 followed Freundlich and Langmuir isotherm models pseudo-second-order kinetics with intra-particle diffusion mechanism. The ΔH°, ΔS° and ΔG° for the processes were '34.5, 64.5 and 22 012.0 kJ/mol, respectively. The adsorbent achieved an adsorption efficiency of above 95.0%, and is thus recommended for industrial application in remediating potentially toxic metals from wastewater. <![CDATA[<b>Rising environmental temperatures and polluted surface waters: the prelude to the rise of mycoses in South Africa</b>]]> South Africa's rivers are frequently used by communities lacking proper sanitation infrastructure for domestic purposes; however, these surface waters may pose a health risk to immunocompromised individuals due to the presence of opportunistic pathogenic fungi in the polluted water. Although only a few studies have focused on the presence of clinically relevant fungal species in South African rivers, many known opportunistic pathogenic species were found to be predominant in these waters. Furthermore, strong evidence exists that increased numbers of clinically relevant species may be observed in future due to fungi acquiring thermotolerance in response to the global increase in temperature. Thermotolerance is a major factor contributing to pathogenesis in fungi, due to the generally low tolerance of most fungi toward mammalian body temperatures. It is therefore contended that combinatorial effects of water pollution and rising environmental temperatures could lead to an increase in the incidence of mycoses in South Africa. This is especially concerning since a relatively large population of immunocompromised individuals, represented mostly by HIV-infected people, resides in the country. <![CDATA[<b>Establishing an economically and biologically sustainable and viable inland fisheries sector in South Africa - pitfalls of "path dependence'</b>]]> Small-scale fisheries play a significant role in livelihoods and food and nutrition security for millions of people around the world. However, these benefits are under threat, especially in developing countries such as in Africa, as a result of poor governance. The historical developmentalist and welfarist approach to management of small-scale fisheries in developing countries, dating back from colonial era, has resulted in problems of open-access regimes that usually lead to over-capitalisation, geographic spread of landing sites that makes it difficult to organise fishers for management activities, inadequate management capacity and poor funding of the sector. These lead to over-exploitation and degradation of fish resources, thereby negatively impacting the current and long-term benefits for small-scale fishing communities and society at large. Most countries that start off with such problematic fisheries management regimes and set on this path find it very difficult to reform the regimes. This article argues that South Africa needs to draw lessons from the mistakes of other (developing) countries in terms of the type of fisheries management regime governing small-scale fisheries, as it sets up and creates a new inland small-scale fisheries sector. Such 'path dependence' can set a country on courses of action and decisions that are extremely difficult to reverse and extricate a country from. There is no doubt of the need for more equitable distribution of access rights and benefits to inland fisheries for communities that had been excluded and marginalised under colonialism and apartheid. However, this has to been done without endangering the fish resources and in effect the very sustainable social-economic benefits that such reforms intend to achieve.