Scielo RSS <![CDATA[Water SA]]> vol. 46 num. 4 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>Assessment of satellite-derived rainfall and its use in the ACRU agro-hydrological model</b>]]> Unfortunately, for various reasons, in-situ rain gauge networks are diminishing, especially in southern Africa, resulting in sparse networks whose records give a poor representation of rainfall occurrence, patterns and magnitudes. Hydrological models are used to inform decision making; however, model performance is directly linked to the quality of input data, such as rainfall. Therefore, the use of satellite-derived rainfall is being increasingly advocated as a viable alternative or supplement. The aim of this study was to evaluate the representativeness of satellite-derived rainfall and its utility in the ACRU agro-hydrological model to simulate streamflow magnitudes, distributions and patterns. The satellite-derived rainfall products selected for use in this study were TRMM3B42, FEWSARC2.0, FEWSRFE2.0, TAMSAT 3.0 and GPM-IMERG4. The satellite rainfall products were validated against available historical observed records and then were used to drive simulations using the ACRU agro-hydrological model in the upper uMngeni, upper uThukela and upper and central Breede catchments in South Africa. At the daily timescale, satellite-derived and observed rainfall were poorly correlated and variable among locations. However, monthly, seasonal and yearly rainfall totals and simulated streamflow volumes were in closer agreement with historical observations than the daily correlations; more so in the upper uMngeni and uThukela than in the upper and central Breede (e.g. FEWSARC2.0 and FEWSRFE2.0, producing relative volume errors of 3.18%, 4.63%, -5.07% and 2.54%, 9.54%, -1.67%, respectively, at Gauges V2E002, 0268883 and 02396985). Therefore, the satellite-derived rainfall shows promise for use in applications operating at coarser temporal scales than at finer daily ones. Complex topographical rainfall generation and varying weather systems, e.g. frontal rainfall, affected the accuracy of satellite-derived product estimates. This study focused on utilising the wealth of available raw satellite data; however, it is clear that the raw satellite data need to be corrected for bias and/or downscaled to provide more accurate results. <![CDATA[<b>Water-use characteristics of Palmiet <i>(Prionium serratum), </i>an endemic South African wetland plant</b>]]> Palmiet, Prionium serratum, is an endemic wetland plant which dominates oligotrophic wetlands throughout the Cape Floristic Region, South Africa. Palmiet is often perceived as undesirable by landowners, in part because it is thought to have high water-use, although little is known about the water-use of this important wetland species. We estimated the water-use dynamics of Palmiet at the leaf scale, using stomatal conductance measurements, and at the wetland scale, by modelling evapotranspiration using remote sensing and an energy-balance model. Factors that influenced Palmiet water-use were also considered, and seasonal variations were analysed. The aim was to estimate Palmiet wetland water-use, and to develop a set of crop factors (Kc) for use in hydrological modelling of catchments containing Palmiet wetlands. Results show that Palmiet has a comparatively low stomatal conductance (11-152 mmol-m-2.s-1), which was lower in summer than winter, and moderate evapotranspiration for a riparian species (1 220 mm-a-1 compared to a local reference evapotranspiration of 1 302 mm-a-1 and A-Pan evaporation of 2 809 mm-a-1), which was higher in summer (more energy to drive evapotranspiration and higher vapour pressure deficits). Morphological and physiological adaptations to nutrient poverty or periodic drought are suggested theories which may explain the controls on transpiration for Palmiet. <![CDATA[<b>Irrigation scheduling for green beans grown in clay loam soil under a drip irrigation system</b>]]> An experimental field trial was conducted at El-Ayat, El-Giza Governorate, Egypt (latitude 30°11"I3"N, longitude 31°41'38"E, and mean altitude 74 m above sea level) during the growing season of 2017 and 2018. The study aimed to assess the suitable irrigation interval and applied water volume for drip-irrigated green beans, based on water production functions and water use-yield relationships. The field trial was arranged in a split-plot design with 3 irrigation intervals (F1, F2 and F3 irrigation events, once every 1, 2 and 3 days, respectively) and 3 irrigation regimes (I1: 1.00, I2: 0.80, and I3: 0.60 of the crop evapotranspiration, ETc). The results showed that the yield and water use efficiency (WUE) increased with increasing irrigation interval. Maximum and minimum yield of 12 030 and 4 879 kg-ha-1 were obtained in F1I2 and F3I3 treatment, respectively, in the winter season of 2017, and were 12 364 and 4 678 kg-ha-1 for the corresponding treatments in the winter season of 2018. WUE ranged from 56.55 kg-ha-1-mm-1 in F1I2 to 23.80 kg-ha-1-mm-1 in F3I3. Plant growth parameters were significantly affected by the irrigation schedule. The highest plant growth parameters were obtained under F1 and F2. The seasonal yield response factors (k y) were 0.845 and 0.856 in 2017 and 2018, respectively. The relationship between yield and seasonal crop ET was best explained by a power function for all irrigation schedules for both growing seasons. It is recommended that the F1I2 irrigation treatment is the suitable one for green beans grown under field conditions, in order to achieve the highest yield and WUE. <![CDATA[<b>Responses of macroinvertebrate community metrics to urban pollution in semi-arid catchments around the city of Bulawayo, Zimbabwe</b>]]> River health monitoring is becoming increasingly important because of the anthropogenic activities that continue to impact on water quality and biodiversity of aquatic systems. This study aimed at identifying and evaluating macroinvertebrate community-based metrics that best respond to degradation due to urban pollution in riverine systems of Bulawayo, Zimbabwe. Data (physicochemical variables and macroinvertebrate specimens) were collected from 17 sites over 3 seasons. The sites were selected across an impairment gradient comprising less impacted, moderately impacted and heavily impacted sites. Heavily impacted sites had the highest levels of total dissolved solids, conductivity, salinity, turbidity, total phosphates, total nitrogen, chemical oxygen demand and sedimentary zinc. Dissolved oxygen was significantly highest in less impacted sites. Sensitivity of 24 macroinvertebrate metrics to this impairment gradient were assessed. A total of 5 metrics were identified as sensitive to modifications in water quality due to urban pollution. These metrics were taxon richness, South African Scoring System (SASS5) score, average score per taxon (ASPT), percentage collectors and percentage scrapers. The selected metrics will be useful for the monitoring and assessment of the studied riverine systems and can be further integrated into one multimetric index that combines a range of indices and allows the integration of ecological information for better management of aquatic ecosystems in this region. <![CDATA[<b>Physico-chemical parameters and culturable yeast diversity in surface water: a consequence of pollution</b>]]> Rivers in the North West Province (NWP) of South Africa are polluted by various anthropogenic activities that are associated with agricultural, domestic, industrial, and mining activities. Pollutants and effluent resulting from these activities impact the physico-chemical and biological characteristics of river water. More particularly, domestic and agricultural pollution has been associated with the occurrence of pathogenic yeast species in water. The aim of this study was to determine physico-chemical parameters, yeast levels, and the antifungal susceptibility of pathogenic yeasts in river water. Physico-chemical parameters and yeast levels were determined using standard procedures. Yeasts were identified by biochemical tests and 26S rRNA gene sequencing. Disc diffusion antifungal susceptibility tests were conducted on identified potential pathogenic yeasts. Physico-chemical parameters were within target water quality ranges (TWQR) for livestock farming but were mostly out of range for irrigation. Yeast levels (incubation at 37°C) ranged from 363 to 1 778 CFU/L. There were significant differences (p < 0.05) in the physico-chemical parameters and yeast levels between some seasons and among the river systems under study. A positive association was observed between temperature, COD and yeast levels in all the river systems. Ascomycetes, which were the most prevalent isolates, were identified as Candida spp. (35%), Pichia spp. (13%), Cyberlinera spp. (12%), Meyerozyma spp. (11 %), Clavispora spp. (10%), Saccharomyces spp. (6%), Kluyveromyces spp. (5%), Yamadazyma spp. (4%), Trichosporon spp. (3%), and Wickerhamomyces spp. (1(0)%). Antifungal resistance of the potential pathogenic yeasts was as follows: flucytosine and miconazole (100%) &gt; fluconazole (78.5%) &gt; econazole, and miconazole and ketoconazole (49.6%) &gt; nystatin (15.2%). The river water systems explored in the study are used for agricultural, domestic and recreational purposes. Direct contact with the water, especially by immune-compromised people, may pose a health threat and should be further investigated. <![CDATA[<b>Correlations between TDS and electrical conductivity for high-salinity formation brines characteristic of South Atlantic pre-salt basins</b>]]> Total dissolved solids (TDS) is an important property in the characterization of natural waters for diversified applications, such as in geochemistry and the petroleum industry. Under appropriate circumstances, the determination of this parameter through correlations with the electrical conductivity (EC) of aqueous systems yields considerable advantages over the gravimetric method. However, the development of empirical equations correlating TDS and EC is still required due to the physical-chemical complexity of charge transport in multicomponent natural waters. Most existing correlations were built considering systems in the lower or medium salinity range. In this context, this research aims to provide experimental correlations between TDS and EC in a broad concentration range for high salinity formation brines characteristic of the pre-salt reservoirs. It contributes to filling a gap in the literature for geochemical systems of this nature. Moreover, correlations were also obtained for a concentrated desulphated seawater and an aqueous sodium chloride solution in the same salinity range. For all aqueous solutions, the polynomial fittings of degree greater than one fit the experimental data better compared to both linear and exponential equations. In addition, the solutions with higher concentration of divalent ions had lower EC than the solutions dominated by monovalent ions with the same ionic strength. This evidences the effect of ion pairing on the EC, particularly in solutions of high ionic strength. Therefore, the use of a general correlation to represent solutions with dramatic variations in chemical composition carries substantial error, particularly in the high salinity range. Thus, a specific correlation must be developed to represent brines with similar composition. <![CDATA[<b>Chemical phosphate removal from Hartbeespoort Dam water, South Africa</b>]]> Phosphate is one of the major nutrients contributing to the increased eutrophication of lakes and natural waters. The feed water to the Hartbeespoort Dam amounts to 650 ML/d of mainly treated sewage. Phosphate levels in the dam water need to be lowered from the current 0.2 mg/L to less than 0.05 mg/L to control eutrophication. Chemicals such as iron(III), iron(II), aluminium(III) and lime can be used to precipitate phosphate as FePO4, Fe3(PO4)2, AlPO4 and Ca3(PO4)2, respectively. OLI software was used to identify the most suitable chemical for phosphate removal. It was found to be Ca(OH)2 as this only requires the pH to be raised to 9.5. FeCl3, FeCl2 and AlCl3 were found to be unsuitable due to the required pH and/or the extent to which they could remove phosphate. For lowering of phosphate levels from 0.2 mg/L (as P), the current concentration in the Hartbeespoort Dam water, to <0.05 mg/L (as P), the minimum concentration that is needed to support algal growth, a lime dosage of 50 mg/L is required. The cost of lime treatment will amount to 0.15 ZAR/m³. It is thus recommended that eutrophication in the Hartbeespoort Dam be controlled by removal of phosphate through lime dosing. <![CDATA[<b>Accelerated phosphorus removal using sulfate-coated expanded vermiculite</b>]]> This study evaluated whether phosphorus in an aqueous solution can be effectively adsorbed and removed by sulfuric acid (SA)-coated vermiculite (SCV), which was synthetized by heating a mixture of expanded vermiculite (EV) and SA at 300°C. Phosphorus was removed from the aqueous solution and removal characteristics were evaluated by batch kinetic, batch adsorption, and column tests. The phosphate removal rates (h-1) for 1, 2.5, 5, 7.5, 12.5, and 25 g-L-1 of SCV were 0.00015, 0.0011, 0.0044, 0.0087, 0.0648, and 0.5002, respectively. The Qmax of the Langmuir model and the partition coefficients of the linear and Freundlich models were 8.92 mg-g-1, 0.65 L-g-1, and 4.60 L-g-1 (1/n = 0.354), respectively. The equilibrium phosphorus adsorptions (q e) were 7.47, 14.69, and 19.53 mg-g¹ at initial concentrations of 10, 25, and 50 mg-L-1, respectively. These results show that SCV can efficiently adsorb phosphorus in an aqueous solution. <![CDATA[<b>Cd(II) biosorption using bacterial isolates from sawdust: optimization via orthogonal array Taguchi method</b>]]> Orthogonal array of Taguchi experimental design with L16 four-level factors: pH (2-8), temperature (303-333 K), time (1-4 h), inoculum concentration (5-20 v/v) and Cd(II) initial concentration (50-200 mg/L) was applied to optimize Cd(II) biosorption from aqueous solution via bacterial isolates from sawdust. The optimum conditions were found to be 4, 303 K, 4 h, 15 v/v % and 50 mg/L for pH, temperature, time, inoculum concentration and Cd(II) initial concentration, respectively. A confirmatory experimental run at these conditions revealed 99.53% Cd(II) removal. Fourier transform infrared revealed the presence of -OH on the bacterial surface enhancing Cd(II) biosorption. The presence of small cavities on the bacterial surface with a porous inner multilayer was shown by scanning electron microscopy analysis. Proposed biosorption mechanisms were electrostatic interaction, surface complexation and ion exchange. In conclusion, bacterial isolates from sawdust could effectively be applied as biosorbent for Cd(II) removal from aqueous solution. <![CDATA[<b>Re-evaluating the strength of pit-latrine faecal sludge from dynamic cone penetrometer test data</b>]]> In 2017, 55% of the global population were without safely managed sanitation services. On-site sanitation solutions, such as pit latrines, provide the majority of sanitation coverage across developing countries. Appropriate technologies are required in order to safely empty these latrines without damage to people or the environment. The design of appropriate emptying technologies can be hampered by a lack of knowledge of the mechanical properties of the waste, such as its strength. This paper will develop a calibration for a dynamic cone penetrometer to give accurate measurements of faecal sludge strength against a standard scale, rendering existing data comparable. It will be shown that the maximum shear strengths of faecal sludge found in practice are substantially greater than those previously reported; some pit latrines contain faecal sludge with strength values of 5-20 kPa at the surface, and exceeding 80 kPa at depth. <![CDATA[<b>An empirical analysis of residential meter degradation in Gauteng Province, South Africa</b>]]> Understanding the degradation rates of water meters assists utilities in making informed management decisions regarding meter replacement programmes and meter technology selection. This research evaluated the performance of 200 residential meters of two different technologies commonly used in Gauteng, South Africa, namely velocity meters and volumetric meters. This was done by conducting empirical meter testing in a verification laboratory and evaluating the degradation accuracy of each meter technology based on age and volume. Results indicate that velocity meters experience an accuracy degradation rate of approximately -1.13% per 1 000 kL of volume passed through the meter and an inferred initial error of -10.80%. Meter accuracy was not strongly related to age of the velocity meters tested. Volumetric meters did not exhibit a strong link with either age or accumulated volume, indicated by a loose grouping of results. These results indicate that accumulated volume of a velocity meter is a more reliable predictor of accuracy than age, and should be used when planning replacement strategies for velocity meters. Additionally, the lack of predictable degradation rates related to either age or accumulated volume for volumetric meters indicates that the accuracy of volumetric meters is primarily affected by other external factors, such as particulates or entrained air in the water network. These findings will assist utility managers in predicting the accuracy of their meter fleet and in making informed decisions regarding meter replacement. <![CDATA[<b>Experimental study and numerical simulation of dam reservoir sediment release</b>]]> In this research, experimental and numerical modelling of three-phase air, water, and sediment transport flow, due to the opening of a sluice gate was conducted in two scenarios, i.e., with and without a triangular obstacle. Numerical simulation was conducted using the Navier-Stokes equations with the aid of the volume of fluid method (VOF) to track the free surface of the fluid. For the experimental model, a glass-enclosed flume with 150 x 30 x 50 cm dimensions was used. The experiment was performed for an initial height of the water column at 20 cm and 10 cm sediment column. To evaluate the numerical model's performance, the simulation results were compared with the experimental observations using the average relative error %. The amount of relative error between experimental observations and numerical simulations, for the position and height of the wave flow for the three-phase air, water, and sediment flow, were obtained as 2.64% and 4.51% for the position and height of the water wave, and 2.23% and 2.82% for the position and height of the sediment transport, respectively, for the 'without obstacle' scenario, and 3.77% and 5.25% for the position and height of the water wave, and 2% and 7.23% for the position and height of the sediment transport, respectively, for the 'with obstacle' scenario. The findings of the study indicate the appropriate performance of the numerical model in the simulation of water and sediment wavefront advance, and also its weakness in the estimation of wave height. <![CDATA[<b>Modelling groundwater level fluctuation in an Indian coastal aquifer</b>]]> Estimating groundwater level (GWL) fluctuations is a vital requirement in hydrology and hydraulic engineering, and is commonly addressed through artificial intelligence (AI) models. The purpose of this research was to estimate groundwater levels using new modelling methods. The implementation of two separate soft computing techniques, a multilayer perceptron neural network (MLPNN) and an M5 model tree (M5-MT), was examined. The models are used in the estimation of monthly GWLs observed in a shallow unconfined coastal aquifer. Data for the water level were collected from observation wells located near Ganjimatta, India, and used to estimate GWL fluctuation. To do this, two scenarios were provided to achieve optimal input variables for modelling the GWL at the present time. The input parameters applied for developing the proposed models were a monthly time-series of summed rainfall, the mean temperature (within its lag times that have an effect on groundwater), and historical GWL observations throughout the period 1996-2006. The efficiency of each proposed model for Ganjimatt was investigated in stages of trial and error. A performance evaluation showed that the M5-MT outperformed the MLPNN model in estimating the GWL in the aquifer case study. Based on the M5-MT approach, the development of this model gives acceptable results for the Indian coastal aquifers. It is recommended that water managers and decision makers apply these new methods to monitor groundwater conditions and inform future planning. <![CDATA[<b>First observation of fouling of externally attached radio transmitters in an African river</b>]]> Fouling of externally attached tags is an important consideration in long-term tagging studies as it may affect fish behaviour and well-being. Two externally attached radio transmitters on African tigerfish Hydrocynus vittatus were covered with short green algae, after the fish were recaptured 49 and 64 days after tagging in the Kavango River, Namibia. This is the first observation of fouling on external radio transmitters from any African river which highlights the importance of conducting studies that evaluate the various health or behavioural effects resulting from tagging. <![CDATA[<b>An examination of the effectiveness of traps and baits as a possible means of harvesting crayfish, <i>Cherax quadricarinatus </i>in Sanyati Basin, Lake Kariba, Zimbabwe</b>]]> Although Cherax quadricarinatus is now established in Lake Kariba, there is a lack of information on the appropriate gear technology and bait for its exploitation for either management or commercial purposes. The effectiveness of three trap designs and three bait types was investigated in order to identify the best means for harvesting C. quadricarinatus in Lake Kariba. The cylindrical and rectangular traps had higher and similar CPUE, which were significantly higher than those of the Opera house trap at all sites. Trap type did not influence sex ratio. Liver, sadza and fish heads were all similarly effective as bait. Either sadza-baited cylindrical or rectangular traps can be effectively employed to either harvest crayfish in order to maintain a low population, thereby mitigating potential adverse impacts, or for commercial purposes. This should be corroborated with monitoring and further research.