2026-01-30
S Schütte, RE Schulze
Water quality in South Africa’s river systems is declining, driven in part by changes in land use and management. Diffuse pollution significantly contributes to river degradation, requiring identification of critical source areas of diffuse pollutants, including nutrients and suspended solids. This study assesses diffuse pollution risks in two contrasting catchments: the Thukela and the Breede. A risk-based assessment was undertaken using the Sensitive Catchment Integrated Modelling Analysis Platform (SCIMAP). SCIMAP integrates a digital elevation model (to determine hydrological connectivity), land use based diffuse pollution potential, here assessed from national land cover classes using the Automated Land-based Activity Risk Assessment Method (ALARM), and rainfall information (representing runoff dilution potential). Results are presented as (i) risk generation of diffuse nutrients based on land use attributes, (ii) the connectivity risk of the movement of pollutants to the river channel, (iii) nutrient risk from the landscape component’s critical source areas, (iv) nutrient concentration risk in the channel component of the catchment, and (v) suspended solid risks from the landscape component. In the Thukela Catchment, landscape-scale nutrient risk patterns were relatively uniform at catchment scale, with distinctions only emerging at finer spatial scales, where elevated risks were associated with some commercial and subsistence agricultural areas. The Breede Catchment exhibited distinct nutrient risk patterns even at catchment scale, with high-risk areas closely linked to some commercial agriculture areas. Channel segments of high nutrient risk for both catchments became evident only at detailed spatial scales. Landscape-based diffuse suspended solids risk areas within the Thukela Catchment range from lows under undisturbed natural vegetation or areas of low connectivity, to highs dominated by degradation and subsistence farming, combined with a high connectivity risk. The Breede Catchment was more muted. This approach is useful to backtrack from polluted river sections to areas with high risk of generating and mobilising pollutants.
2026-01-30
Chisanga Lyoba, Greyford Tembo, Misheck Chundu, Kawawa Banda, Imasiku Nyambe
Wetlands are vital to healthy ecosystems as they control floods and perform other important roles. Globally, the primary cause of wetland degradation is land use–land cover (LULC) change, a situation that also applies to Zambia. This research investigated LULC changes in the Bangweulu Wetland and its perceived drivers, using remote sensing, geographic information systems (GIS), questionnaires, and key informant interviews. The land was categorized into five types: settlements, grassland, cropland, water, and forest. The results showed a decline in forest (from 45 298.93 km² to 33 233.52 km²), grassland (from 32 557.91 km² to 26 418.19 km²), and water (from 2 410.72 km² to 2 278.31 km²) between 1990 and 2020. In contrast, settlements grew from 356.69 km² to 2 210.38 km², and cropland expanded from 165.27 km² to 5 108.13 km². The perceived drivers of this change were also identified. Population growth was the most significant (3.76/5), followed by settlement expansion (3.66/5), declining ecosystem services (3.57/5), and forest loss (2.64/5). Minor perceived drivers included the built environment (2.21/5), recreation (1.54/5), and industry (1.34/5). Underlying causes involved agricultural development and energy needs, driven by market demands for charcoal and cash crops, which accelerate farming and deforestation. Understanding these local perspectives is essential for creating effective land management strategies and sustainable policies to conserve the Bangweulu Wetland's ecological functions.
2026-01-30
Abdessalam Radjai, Mourad Amara, Fouzia Houma, Hafida Hadjar, Safia Chernai, Saifi Amirouche, Boualem Hamdi
This study focused on the fouling of two seawater reverse osmosis (SWRO) membranes at the Beni Saf Water Company desalination plant in Algeria, which has a daily capacity of 200 000 m 3 and a recovery rate of 45% using 17 920 membranes. Approximately 3 234 membranes are replaced annually due to fouling. A detailed study of the fouling agents of the two membranes was conducted using various analytical techniques, such as moisture analysis, loss on ignition (LOI), determination of calcium carbonate (CaCO 3 ) content, x-ray fluorescence (XRF), x-ray diffraction (XRD), and Fourier-transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR). Surface characterization was also performed using scanning electron microscopy equipped with energy-dispersive x-ray spectroscopy (SEM-EDS), FTIR-ATR, and XRD. The LOI analysis indicated that more than 30% of the fouling material was organic in nature. FTIR-ATR identified the presence of –OH groups, phenolic C–O groups, and amide bonds, suggesting the accumulation of organic substances such as proteins, humic substances, and polysaccharides. Additionally, SEM-EDS, XRF, and XRD revealed relatively high concentrations of silica, primarily in the form of quartz, confirming the formation of an organo-inorganic complex on the membrane surface. Based on these findings, a sequential chemical cleaning protocol was developed, incorporating alkaline (NaOH), metal chelator (EDTA), surfactant (SDS), oxidant (H 2 O 2 ), and sulfuric acid (H 2 SO 4 ), each followed by rinsing with deionized water (DI). This cleaning regime effectively removed fouling from the membrane surface, resulting in an average weight loss of 15% for one membrane and 14% for the other.
2026-01-30
John Okedi, Neil Philip Armitage
The City of Cape Town in South Africa faced the possibility of taps running dry in 2018 due to a prolonged drought that commenced in 2015. With such droughts expected to reoccur frequently in future, this study investigated the prospects for managed aquifer recharge (MAR) with stormwater. This would require temporary storage to collect and hold the stormwater during and immediately after rainfall events while it seeps into the aquifer. The 89 km 2 Zeekoe Catchment located in the southern part of Cape Town was selected as a case study as it had both existing surface storage (61 stormwater ponds) and was lying above a large unconfined aquifer. As the stormwater ponds were largely designed for flood control, they would need to be modified for MAR. In this desktop study, the main objective was to model temporary detention of stormwater in the ponds with the aim of predicting infiltration into, and thus augmentation of, the aquifer. The requirement that the flood control function be maintained, combined with the limited capacity in the ponds, was a key consideration. The study determined that the physical characteristics in the Zeekoe Catchment, i.e., largely flat terrain, pervious sandy soils, and a relatively deep (20–50 m) unconfined aquifer, could support managed aquifer recharge and borehole abstraction rates of 3.5–8.1 L/s per borehole from some 140 boreholes. This could provide a mean annual groundwater yield of 29–33 Mm 3 (about 15% of Cape Town water demand in 2018).
2025-10-31
Annelieke Duker, Diego Zuluaga Velásquez, Pooja Prasad, Charlotte de Fraiture, Gabriela Cuadrado Quesada
Sand harvesting is an economically lucrative business but poses hazards to riverine ecosystems and their inhabitants. In the sand rivers of sub-Saharan Africa, sand harvesting results in depletion of water resources used for agriculture, alongside increased erosion and destruction of agricultural lands and riparian vegetation. Sand harvesting occurs within a complex web of actors and interests, often with injustices and inequities in resource use. This study examines the impact of sand extraction on farming families and their livelihoods. It evaluates how a riparian farming community related to unregulated sand removal from a sand river in Kenya, resulting in a violent conflict. Based on surveys and semi-structured interviews, we evaluate the different impacts of sand harvesting on irrigated agriculture and the coping strategies of farmers. Also, we analyse the interactions between the efforts of the community and the governmental institutions in addressing the violent conflict and in restoring the river ecosystem. We find that excessive sand harvesting led to a depletion of water resources, forcing smallholder irrigators to cease farming operations. Using an environmental justice perspective, we find that grassroots actions evolved into a trigger for local government to curb sand harvesting conflicts and support river restoration. In conclusion, conflict served as a force to induce sustainability, impelled by a critical interplay of actions by community and the newly decentralized government. In this process, grassroots movements were not uniform and resistance was not a straightforward process, but one in which individuals changed position, opinion and alliances over time.
2025-10-31
C Musekiwa, C Penn-Clarke, L Nhleko, A Charles, Z Phikiso, T Dhansay
This study focused on the creation of a groundwater potential zones (GWPz) map for an area around the town of Franschhoek, Western Cape Province, South Africa. Parameters including lineament density, aquifer type data, distance to rivers, slope, land use land cover and rainfall were integrated using the geographic information system multi-criteria decision making (GIS-MCDM) weighted overlay method to create the map. Lineaments were obtained from existing geology maps and remote sensing datasets including ArcGIS basemaps, Satellite Pour l'Observation de la Terre (SPOT) 6, Landsat 8, Sentinel-2, Advanced Land Observing Satellite Phased Array type L-band Synthetic Aperture Radar (ALOS PALSAR) and airborne hyperspectral data. On the GWPz map, high potential zones covered 21% of the area, medium potential zones 42%, low potential zones 27%, and 10% had very low potential. 74% of the boreholes were drilled in the medium and high potential zones. Seismic and stress data were integrated with the GWPz and lineaments and the results showed that areas with high groundwater potential at the intersection of northeast–southwest lineaments would be good exploration targets. Sensitivity analyses involved creating scenario maps based on various weighting options and evaluating the results using Kappa and Pearson correlation coefficients and area under the receiver operating characteristic (ROC) curve (AUC). The scenario maps showed moderate to high correlation (0.67 to 0.96) and Kappa coefficients (23% to 75%) indicated fair to substantial agreement amongst the maps. AUC values ranging from 46% to 66% showed that the models’ abilities to distinguish between the classes ranged from poor to average. The results showed that although the map changes with variations in parameter weights and classification, the high groundwater potential zones are not significantly affected. The findings of the study will assist decision makers in identifying suitable exploration areas, enabling efficient planning, allocation and management of resources.
2025-10-31
Editor
2025-10-31
Gavin Melvin Oberem, J Snyman, EA Burger
Urbanization has placed pressure on urban stormwater infrastructure. Previously implemented stormwater master planning had become inadequate in managing floods. Research has shown that the use of sustainable drainage systems (SuDS) assists in mitigating the effects of the change in impervious areas brought about by urbanisation. While research on the usage and functions of SuDS is widely available, there is a lack of literature on the impact of indigenous ground cover categories in reducing stormwater runoff within bioswales in South Africa. The aim of this study was to evaluate the impact of indigenous ground cover categories on the hydrological performance of a bioswale in reducing stormwater runoff volume and peak. A physical simulation model was constructed to assess the water balance of the bioswale, taking into account the soil water content of the engineered soil medium. The effects of the inflows in the simulation model were addressed by mimicking the 1-in-10-year post-development return period stormwater runoff scenario, within the Gauteng Province, South Africa, during the summer rainfall pattern. The lawn category (kweek / Cynodon grass) demonstrated an average volume reduction of 54.7%, with a peak flow reduction of 49.9%. Ornamental grasses and veld grasses also exhibited a volume reduction (42.2% and 38.0%, respectively) and peak flow reduction (40.4% and 38.3%, respectively). Additionally, these grass categories influenced the soil water content. Overall, these findings demonstrate that there is potential for various grass types to mitigate stormwater runoff.
2025-07-22
Mark R Jury
The intensity of dry spells in South Africa is evaluated with monthly European Reanalysis potential evaporation which describes the rate of soil moisture depletion. Filtered time series of potential evaporation averaged over eastern South Africa for 1960–2022 provide a basis for meteorological analysis. After ranking, a representative dry summer (Oct 2018 – Feb 2019) and case study (10–14 Dec 2018), emerged. The synoptic circulation was dominated by upper level equatorward airflow and mid-level subsidence of −0.1 m/s. Back-trajectory analysis shows how warm, dry, dusty air spreads eastward from the Namib Desert to the Orange River Valley, while sinking from 3 000 to 1 000 m. Diurnal evaporation exceeded 0.6 mm/h and dewpoint temperatures of −9°C were recorded in the Free State Province. Global statistics confirm that Pacific El Niño and warm phase Indian Ocean Dipole lead to unusually dry summer weather. Terrestrial runoff and river discharge across eastern South Africa are equally correlated with rainfall and potential evaporation (±0.74), suggesting that operational monitoring and applied research should put greater emphasis on hydrological losses and surface water demand.
2025-07-22
Hassan Bukhari, Alison Joubert, Cate Brown, Karen J Esler
Interactive, ecosystem-based environmental flow models provide stakeholders with a wide range of useful information, such as scenario analysis of trade-offs between social and ecological impacts and river infrastructure expansion for various development pathways. However, their adoption remains restricted in data-limited environments partly because of the difficulty in developing the driver-response relationships that form the heart of ecosystem-based models. Such relationships describe ecological responses to environmental drivers and are perceived to have limited transferability from previously studied river basins. To test this perception, this study extracted and synthesized expert-derived ecosystem indicators and driver-response relationships developed for 63 sites across 20 rivers in southern Africa and evaluated the factors that determined transferability of indicators and relationships between river sites. The assessment revealed that, in general, ecosystem indicators and responses were not dictated by river type (in terms of longitudinal zone, broad habitat type, and valley slope) as calculated by continental scale datasets available for southern Africa. Instead meso-habitats played a key role in determining the ecosystem indicators and links between them. Riparian vegetation and macroinvertebrate indicator guilds had functionally similar links even as the species and underlying river type varied between sites. Expert-derived driver-response relationships were found to be convergent across a range of specialist teams and project time allocations. These findings support the spatial transferability of driver-response relationships for scenario analysis across southern Africa. Further, they provide the foundation for the development of generic ecosystem indicators and driver-response relationships for geomorphology, riparian vegetation, macroinvertebrate and fish indicators that can be used for rapid environmental flow assessments of rivers to support informed decision making related to river infrastructure development.
2025-07-22
M Appolus, A Bosman, GR Basson
A 1:15 scale physical hydraulic model was designed and constructed to investigate the incipient failure conditions of large angular riprap. A total of 32 tests were performed on angular riprap dumped on steep bed slopes of 0.333 to 0.5, and against a steep side-bank slope of 0.4 in a wide trapezoidal channel. The critical movability number value defining the critical incipient failure conditions of angular riprap on steep bed slopes and steep side-bank slopes was determined to be 0.12 and 0.227, respectively. Based on the HEC-RAS 1-dimensional (1-D) steady-state flow analysis, it was identified that HEC-RAS overestimates the critical incipient failure movability number of the steep bed and steep side-bank riprap by a critical factor of 1.91 and 1.35, respectively. The applicability of the study’s findings is limited to prototype riprap D 50 sizes of 0.57 m to 1.125 m, and a trapezoidal canal bottom-width to D 50 ratio of 16:31 ( W base : D 50 ).
2025-07-22
Abdellah Ben yahia, Iman Kadir, Abdelaziz Abdallaoui, Kaoutar Elazhari
This study aimed at establishing a powerful model, using multilayer perceptron (MLP) artificial neural networks, while optimizing database distribution, hidden layer quantity, and node number with the Levenberg–Marquardt learning algorithm, to predict relative humidity in Tangier city, Morocco. The study used a meteorological database with daily readings of 7 variables to predict the output of relative humidity, recorded between January 1985 and December 2022 (13 869 days). The efficacy of the developed models was evaluated by contrasting performance metrics, including coefficient of correlation and mean square error. The best MLP model for the prediction of relative humidity in Tangier has a [7-13-1] architecture, where the hidden layer uses the 'Tansig' function and the output layer uses the 'Purelin' function. The optimized model's efficiency is demonstrated by performance metrics: R = 0.983 and MSE = 0.00295. This MLP model is more efficient than the models established by multiple linear regression, S-MLR and MLR ( R ≈ 0.930; MSE ≈ 10.12). These results have practical applications for better understanding and adapting to climate variations in this region.
2025-07-22
PN Mashaba, WJ Myburgh, MD Panagos
The spatio-temporal changes over a 25-year period in the plant communities associated with the macro-channel of the Olifants River in the Mesic Highveld Grassland in the Mpumalanga Province, South Africa, were investigated. An area-based variable belt transect was used to resurvey selected sites which were previously surveyed roughly 25 years ago. Species richness increased from upstream to downstream driven by high influxes from specifically herbaceous species. Trends in vegetation cover varied from an increase in canopy cover in the upstream plant communities to a decrease in mid-to-downstream plant communities. The woody component increased in upstream communities, altering the riparian vegetation structure within the Grassland Biome section and resulting in spatial changes. The observed human-induced disturbances, such as livestock grazing, fire and river regulation, in conjunction with natural disturbances such as floods, contributed to the observed spatio-temporal changes. This study establishes a foundation for examining various disturbances, ranging from local to landscape levels, to develop research-based management guidelines tailored to different land uses.
2025-04-30
Yassin TH Mehdar
Polyethylene terephthalate (PET) is currently the most widely used type of plastic. PET plastic benefits include that it is lightweight, safe, cheap, and recyclable. Drinking water is an important route for human exposure to contaminants. One method of exposure is through leaching of antimony (Sb) from polyethylene terephthalate PET plastic. Antimony is a toxic element which causes harmful symptoms such as respiratory irritation, dysphagia, vomiting and eye and mucous membrane irritation. Leaching of antimony from three commercially available PET plastics was investigated in this study. The potential leaching of Sb was observed under different pH values, temperatures, and storage times. In this study, elemental mapping using scanning electron microscopy–energy dispersive x-ray spectroscopy (SEM–EDX) and inductively coupled plasma–optical emission spectrometry (ICP–OES) were employed to determine the weight percentages of antimony (Sb) on the inner surfaces of the PET plastic. The results revealed the presence of Sb in PET material, with significantly higher concentrations in PET 3, measured at 0.844 μg/L. Temperature and pH were investigated as factors influencing Sb leaching over time. The concentrations of Sb in bottled water ranged from 0.02 to 2.14 μg/L at different temperatures (25, 40, 50, or 60°C) and from 0.02 to 1.9 μg/L at pH values (6.5, 7, or 7.5) over 200 days. The maximum Sb concentrations reaching 2.14 μg/L at 60°C after 200 days, exceeded the Japanese limit of 2.00 μg/L. These findings highlight the potential health risks associated with Sb leaching from PET bottles, particularly under elevated temperature and low pH conditions.