Showing papers in "Water SA in 2001"

Assessment of the impact of point source pollution from the Keiskammahoek Sewage Treatment Plant on the Keiskamma River - pH, electrical conductivity, oxygen- demanding substance (COD) and nutrients

Abstract: The treatment performance of the Keiskammahoek Sewage Treatment Plant (KSTP), was assessed in terms of pH, conductivity, and COD and nutrients removal from the influent The contributions from this and other smaller point sources in the town to the se parameters in the receiving Keiskamma River were determined by simultaneously monitoring the parameters in the river over a period of about 1 month The COD and orthophosphate in effluents exceed the SA Effluent Quality Standards for these parameters in effluents to be discharged into a river Also, significant pollution of the receiving Keiskamma River was indicated for orthophosphate, COD and NH 4 -N

Survey of heavy metals in the sediments of the Swartkops River Estuary, Port Elizabeth South Africa

Abstract: Elevated levels of heavy metals in the sediment can be a good indication of man-induced pollution. Concentrations of chrome, le ad, zinc, titanium, manganese, strontium, copper and tin were measured in the sediments taken along a section of the Swartkops Rive r and its estuary. These results showed that the highest heavy metal concentrations in both the estuary and river were recorded at points where runoff from informal settlements and industry entered the system. Comparison of the results for the estuary with those obtained in a similar survey made about 20 years ago revealed some remarkable increases. This raises concern over the long-term health of the Swartkops River ecosystem. The Swartkops River catchment contains almost the entire municipal area of Uitenhage and Kwanobuhle, Despatch and Ibhayi and also half of the Port Elizabeth municipal area. It is estimated that approximately one million people live and work presently in the Swartkops River catchment. The Swartkops catchment not only contains the greatest part of the metropolitan population, but it is also the area where the greatest diversity of urban users is found and where urban growth is most rapid. High- density, low-income housing is developing in the catchment with a concomitant increase in industry, and in the quality and quantity of stormwater runoff. These developments will also necessitate the building of further road and rail crossings over the river as well as developing more telecommunication links and power supply lines (Horenz, 1988). The occurrence of elevated levels of trace metals especially in the sediments can be a good indication of man-induced pollution and high levels of heavy metals can often be attributed to anthropogenic influences, rather than natural enrichment of the sediment by geological weathering (Davies et al., 1991; Lord and Thompson, 1988). There can be significant temporal and spatial variability in water column concentrations of heavy metal contaminants, which leads to problems in obtaining representative samples. Sediments, on the other hand, integrate contaminants over time and are in constant flux with the overlying water column. The analysis of heavy metals in the sediments permits detection of pollutants that may be either absent or in low concentrations in the water column (Davies et al., 1991), and their distribution in coastal sediments provides a record of the spatial and temporal history of pollution in a particular region or ecosystem. Heavy metal concentrations in the water column can be relatively low, but the concentrations in the sediment may be elevated. Low level discharges of a contaminant may meet the water quality criteria, but long-term partitioning to the sediments could result in the accumulation of high loads of pollutants. It has been estimated that about 90% of particulate matter carried by rivers settles in estuaries and coastal areas (Martin and Whitfield, 1983). Once heavy metals are discharged into estuarine and coastal

Situation analysis of water quality in the Umtata River catchment

Abstract: The Umtata River was characterised by using standard physico-chemical and microbiological methods to assess the present water quality in the river. The results indicated high turbidity, gross microbiological and cadmium pollution. Turbidity values ranged from 0.28 NTU to 1 899 NTU highlighting the known problem of donga erosion in the catchment. Faecal coliform counts varied between 0 and 21 000 counts/100 ml while the total coliform counts ranged from 0 to 69 000 counts for all the sites sampled. The levels of cadmium varied between 0.01 mg/l and 1.0 mg/l. Nutrient levels were also high. Nitrate values ranged from 0.01mg/l to 28.0 mg/l as N while phosphate values varied between 0.02 mg/l and 5.0 mg/l as P. The high coliform counts and the nutrient values exceeding acceptable limits are indicative of pollution from domestic wastes from several informal settlements located along the riverbank. Water uses in the area were determined and were found to be mainly domestic and recreational. The gross pollution of the river exposes the local people who depend on it for their primary water source to serious health risk. Another use included livestock watering. WaterSA Vol.27(4) 2001: 467-474

A hydrological perspective of the February 2000 floods : A case study in the Sabie River Catchment

Abstract: The exceptionally heavy rains which fell over the north-eastern parts of South Africa, Mozambique and Zimbabwe during February 2000 resulted in disastrous flooding, loss of hundreds of lives and severe damage to infrastructure. The objective of the study reported in this paper is to assess the severity, from a probabilistic perspective, and spatial variability of the extreme rain fall and flooding which occurred in the north-eastern part of South Africa during February 2000. This is performed for events ranging fr om 1 to 7 days in duration using the Sabie River catchment, upstream of the South African/Mozambique border, as an example. The analyses indicate that the floods experienced in the Sabie catchment during February 2000 were the result of rare rainfall with return periods in excess of 200 years in parts of the catchment. The extent of the extreme rainfall increased for longer durations. The magnitudes of the February 2000 floods were such that many gauging stations did not function and numerous gauging structures were inundated. Hence, a modelling approach was adopted to investigate the spatial variability, magnitudes and probabilities of the floods which occurred during February 2000 in the Sabie catchment. The return periods of simulated runoff depths for durations of 1 to 7 days generally exceeded 50 years for the upper and middle portions of the catchment and 200 year s in some parts of the Sabie catchment. Hence, some extremely large and rare flow depths were experienced and the spatial variabi lity of the return periods associated with the simulated runoff depths varied substantially within the catchment.

Comparative water use of wattle thickets and indigenous plant communities at riparian sites in the Western Cape and KwaZulu-Natal

Abstract: Large-scale funding by both the Government and the private sector continues in support of the Working-for-Water Programme, which is active in many regions of the country. One justification for this programme of alien tree removal is the streamflow enhancement that is believed to follow the replacement of dense stands of invasive trees by indigenous, largely herbaceous or shrub dominated plant communities. Often the densest stands of invader trees occur within riparian zones, where removal of trees in close proximity to stream channels is believed to strongly enhance streamflow. Few data are available, however, to support this assumption. Results from a number of research catchments have consistently shown that afforestation significantly decreases streamflow where the pre-afforestation vegetation was seasonally dormant mountain grassland or fynbos (Versfeld, 1994). The net difference in evapotranspiration (ET) between riparian thickets of alien trees and riparian fynbos may be quite different, due to the yearlong availability of soil water and enhanced plant growth in riparian zones. The water use of alien invasive trees in South Africa remains largely unknown, adding further uncertainty to the effect of alien removal on streamflow. This paper describes the results of a comparative study of annual ET between indigenous riparian plant communities and riparian wattle thickets (Acacia mearnsii() at four sites in the Western Cape and KwaZulu-Natal. The Bowen ratio energy balance (BREB) technique was used to record a 12-month record of 20 min evaporation rates from a fynbos riparian plant community in the Jonkershoek valley (Western Cape), and a grassland riparian community on the property Gilboa in the KwaZulu-Natal midlands. Closed-canopy, mature stands of self-established (A. mearnsii( in the Wellington and Groot Drakenstein areas of the Western Cape were selected to provide comparative transpiration data. The heat pulse velocity (HPV) technique was used to record hourly sap-flow rates in six sample trees representing the range of tree sizes at both wattle sites. Total daily sap flow in all sample trees experiencing adequate soil water availability was found to be very closely correlated to tree size and an index defined as the product of mean daily vapour pressure deficit (VPD) of the air and the number of daylight hours. These relationships were used to predict the water use of wattle thickets at Jonkershoek and Gilboa, using VPD and day-length data recorded at these sites. Published estimates of canopy rainfall interception were added to the sap flow (transpiration) component to yield a combined annual ET to compare to the BREB ET data. Table 1 summarises the annual evapotranspiration at each site. (table***) We conclude that the removal of riparian wattle and its replacement by indigenous herbaceous plants may indeed result in significant reductions in annual ET, and could very likely lead to streamflow enhancement. However, this study has clearly shown that annual ET varies considerably in different riparian plant communities, and that one must consider the structural and physiological characteristics of both the pre-clearing and post-clearing vegetation in order to predict the net change in ET. This conclusion supports an earlier view (Versfeld et al., 1998) that an improved methodology of general applicability is required to enhance the accuracy of water use predictions for a wide range of alien and indigenous plant communities. Such predictions are important to prioritise clearing operations in areas invaded by alien trees. WaterSA Vol.27(4) 2001: 529-538

Estimating potential impacts of a change in river quality on the tourism value of Kruger National Park: an application of travel cost, contingent and conjoint valuation methods.

Abstract: Development and resource allocation decision processes are increasingly under pressure to take environmental values into account in order to reach optimal economic outcomes. In South Africa new techniques will be needed to incorporate environmental values into environmental impact assessment and in the allocation of water resources under the new National Water Act (1998), both of which require the comparison of alternative scenarios with varying impacts on the environment. This study on the tourism value of rivers in the Crocodile Catchment is the first case study to develop methods for incorporating the economic values of the goods and services provided by functioning aquatic ecosystems into such decision processes. Rivers within the Kruger National Park (KNP) will be affected by water usage in the portions of their catchment areas upstream of the park boundary. The current tourism value of these rivers was considered in terms of revenues to KNP (visitors' on-site expenditure), contribution to the economy (visitors' on-site and off-site expenditure) and recreational value, including consumers' surplus. The effect of a change in river quality was determined using a joint contingent valuation - conjoint valuation approach, whereby respondents rated four different scenarios, each containing four attributes at four different levels. It was estimated that the current value of KNP tourism is about R136 m. in terms of on-site expenditure, R267 m. in terms of economic impact, or all expenditure related to visiting the park, and R1 bn. in terms of consumers' surplus. The latter two values can be added to calculate total recreational value. Four methods were used to isolate the value of rivers from the total tourism value stated above, and all yielded similar values of about 30% of the total. This implies that about 30% of tourism business would be lost if rivers were totally degraded. Thus, rivers within the Crocodile Catchment, which takes 22% of KNP visitor-nights, contribute R9 m. to KNP revenues and have a total annual recreational use value of about R85 m., including off-site expenditure and consumers' surplus. The conjoint analysis generated an equation which is able to predict the change in trip expenditure, or total KNP revenue, associated with changes in levels of any of the four attributes considered. Appearance of the riverscape has the greatest influence on recreational use value, followed by waterbird diversity, aquatic megafauna and riparian tree density. Such models can be used in water allocation decision processes when attribute levels associated with alternative management scenarios are predicted by aquatic ecologists. WaterSA Vol.27(3) 2001: 387-398

Estimation of recharge using a revised CRD method

Abstract: The cumulative rainfall departure (CRD) method, based on the water-balance principle, is often used for mimicking of water level fluctuations. Because of its simplicity and minimal requirement of spatial data, the CRD method has been applied widely for estimating either effective recharge or aquifer storativity, and consequently gained a focus in South Africa. This paper critically reviews this method and proposes expanded algorithm. Validation of the method under typical South African conditions is discussed based on model-generated and known cases. The study is aided with a user-friendly Excel program called Recharge Estimation Model in Excel (REME).

A review of characterisation requirements for in-line prefermenters : Paper 2 : Process characterisation

Abstract: The operational factors having a significant effect on in-line prefermentation efficiency include the sludge recycle rate and t he subsequent sludge elutriation rate, solids concentrations and retention times. The prefermenter configuration employed is a determining factor, which allows for some degree of operational flexibility. Side-stream and multiple tank systems are superior in this regard and outnumber the use of in-line single tank prefermenters, which are mainly employed due to lower space and capita l cost requirements. This paper reviews the basic design and monitoring requirements for in-line prefermenters, to establish simp le strategies on which prefermenter evaluations could be based.

Treatment of pulping effluents by using alum and clay - Colour removal and sludge characteristics

Abstract: The effect of clay addition during alum coagulation, on the removal of colour from pulp-and-paper industry wastewaters, was investigated. Four types of clay, namely beige-and brown-sepiolites, calcium- and sodium-bentonites of different mesh sizes we re used. Different quantities of alum and clay were applied, either singly or in combination, to the effluents of the wood-based pulpand-paper mill. Colour of the treated wastewater, the sludge volume index (SVI) and sludge cake resistance (SCR) of the sludge produced were monitored. It was observed that the clays tested were not efficient in colour removal when they were applied on their own. When clay was added along with alum, a certain increase in colour removal efficiency was obtained as compared to alu m alone. When alum was used in conjunction with clay, settling characteristics of the sludge produced improved substantially, in terms of both SVI and SCR. Acid activation of the clays did not improve the colour removal efficiency further. However, acid activa tion of sodium bentonite caused the SVI and SCR values to improve considerably compared to virgin sodium bentonite. Use of differen t mesh sizes of clays did not exert any significant effect on the colour removal. However, it did exert significant effects on S VI and SCR values as such that the increase in mesh size caused the SVI values to decrease and the SCR values to increase.

Indicators of sustainable development for catchment management in South Africa - Review of indicators from around the world

Abstract: Indicators are the ideal means by which progress towards sustainable development can be measured. However, most indicator initiatives throughout the world have been aimed at state-of-the-environment reporting, with relatively few aimed at developing sectoral indicators. This paper provides the results of a review to establish trends in the development of indicators that assi st in integrated water resource management. Twenty-one organisations from around the world were approached with regard to whether they had developed indicators of sustainable development for catchment management. Of these, only five organisations had developed, or were in the process of developing, indicator sets that were available for review. These included the Fraser Basin Council (Canada), the Murray-Darling Basin Commission (Australia), the Tennessee Valley Authority (USA), the United States Environmental Protection Agency and the World Resources Institute. All of these indicator sets were developed using an issuesbased approach. Each indicator set was unique, reflecting the policy, both national and organisational, upon which it had been based. An analysis of these five indicator sets revealed that the most important themes that required information for water resource management at a catchment level, were biodiversity and ecosystem integrity, land-use change, water quality, waste production, water availability and resource use. Common indicators included population growth; community involvement; water availability; water use; water quality trends; soil contamination; non-compliance; species at risk; key species assessment; change in vegetat ion; agricultural impact; access to recreational opportunities, and ecosystem health. The identification of these themes and common indicators will be useful for the development of indicators for catchment management in South Africa. More importantly, policy frameworks and the physical characteristics of catchment systems in the country need to be taken into account. Additionally, it is recognised that no effective indicator set can be developed without the input of stakeholders.

Treatment of grain distillation wastewaters in an upflow anaerobic sludge bed (UASB) system

Abstract: In operation of the full-scale upflow anaerobic sludge bed (UASB) system at the Stellenbosch Farmers’ Winery (SFW) Wellington distillery, a problem encountered in the treatment of grain distillation wastewater was the accumulation of a floating scum lay er. On occasion this was so severe that it forced shutdown of the UASB system to facilitate the physical removal of the scum. A preliminary investigation indicated that the scum-layer behaviour could be replicated at laboratory-scale. Thereafter, two laboratory-scale UASB systems were run in parallel: one (control) receiving wine distillation wastewater as influent, and the o ther (experimental) grain distillation wastewater at both high and low total suspended solids (TSS) concentrations. Scum-layer accumulation, COD removal and concentration profiles along the axis of flow through the reactors were compared. The scum layer developed only with grain distillation wastewater as influent, and its severity appeared to be linked to the TSS content of the grain wastewater. Reducing the TSS by drum filtration, settling or blending with wine wastewater could reduce, but not eliminate, th e scum-layer accumulation. With wine distillation wastewater as influent, concentration profiles exhibited the typical three dis tinct zones of sludge bed behaviour. However, with grain distillation wastewater as influent, the concentration profiles were marked ly different; the three zones of behaviour did not develop. This raises the question of the long-term viability of a UASB system treating grain distillation wastewaters.

Flood frequency analysis at ungauged sites in the KwaZulu-Natal Province, South Africa

Abstract: Use of the index-flood method at ungauged sites requires methods for estimation of the index-flood parameter at these sites. This study attempts to relate the mean annual flood to site characteristics of catchments in KwaZulu-Natal, South Africa. The ordinary, weighted and generalised least square methods for estimating model parameters are compared and found to perform equally well, with preference given to the generalised least square model. A separation of KwaZulu-Natal (KZN) into two regions was found to improve predictive ability of the models in the western and north-western parts of the study area. The study also revealed problems with the estimation of the mean annual flood in the coastal areas of the study region.

The impact of irrigation return flow on aspects of the water quality of the upper Gamtoos Estuary, South Africa

Abstract: Groundwater quality in the Loerie Flats, and subsurface irrigation return flow to the upper Gamtoos estuary was monitored from November 1992 to April 1994. The nutrient loading of groundwater was highly variable both spatially and temporally, with elevat ed nitrate-N levels reaching 163 mg·l -1 . The elevated nutrient concentrations in the groundwater were directly related to the timing of land-surface application of fertilisers. The nutrient loading to the estuary, via subsurface irrigation return flow was calcula ted using Darcy’s equation together with the mean concentration of nutrients found in groundwater in the Loerie Flats area. Results indic ate that an average of 0.52 t nitrate-N, 0.02 t nitrite-N and 0.10 t of total phosphorus enter the Gamtoos estuary from the 5.5 km 2 Loerie Flats area on an annual basis. Such nutrient loads emanate from less than 20% of the total agricultural area bordering the estu ary. Despite the elevated nutrient input to the estuary via groundwater discharge, the nutrient content of the estuary was generally low, but at times elevated concentrations of nutrients were recorded in the upper estuary. It was found that estuarine mixing proces ses and dilution, with adequate flushing have prevented the periods of low quality water from persisting in the Gamtoos estuary.

Some factors governing the water quality of microtidal estuaries in South Africa

Abstract: The role of coastal geomorphology and Man-made alterations, including reduced river flow through dam construction, determines, at least in part, the water quality of South African microtidal estuaries. To offer increased understanding of the manner in wh ich these features may modify water quality, a short description of the biogeochemical processes in estuaries is provided. Comment on the present limitations of modelling some of the estuarine processes in South African investigations is given. Nomenclature aeolian transported by wind DO dissolved oxygen DOC dissolved organic carbon DON dissolved organic nitrogen DIN dissolved inorganic nitrogen DOP dissolved organic phosphorus DIP dissolved inorganic phosphorus EFR estuarine flow requirement - pertaining to required river flow Eh redox potential expressed in millivolts MAR mean annual rainfall MSL mean sea level N:P normally the value of the ratio of total soluble nitrogen to total soluble phosphorus in the water column ppt parts per thousand - with respect to seawater, meaning kg of salts per kg of solution. POC particulate organic carbon POM particulate organic matter PON particulate organic nitrogen SRP soluble reactive phosphate TDL theoretical dilution line which represents a linear dilution of a solute as it passes through the estuary - such solutes are termed ‘conservative’.

Modelling of a falling sludge bed reactor using AQUASIM

Abstract: The recycling sludge bed reactor (RSBR) allows for increased solids retention time, resulting in greater substrate conversion f or all particulate degradation and biological reactions. The purpose of the RSBR is to hydrolyse primary settled sewage (PSS). Sol uble products are then used for the biological treatment of acid mine drainage. A mathematical model has been developed that describ es the anaerobic digestion of PSS and biological sulphate reduction in the RSBR. The hydrodynamic processes taking place in the RSBR have been simulated using a system of mixed reactors connected by water flow and mass flux streams. Trends obtained from varying the hydraulic retention time, the sludge recycle ratio, and the feed COD: SO 4 2- ratio allow for identification of the critical biological processes taking place in the RSBR, as well as the influence of the operating parameters. Areas where there is a lac k of understanding in the mechanism and kinetics have been identified, and these include the influence of sulphate reduction on the hydrolysis of particulate organic matter, as well as the mathematical influence of sulphide inhibition on the various biologica l groups. A sensitivity analysis shows that hydrolysis is the rate-limiting process, while sulphide inhibition is of importance w hen sulphate conversion increases.

Pretreatment of urban wastewaters in a hydrolytic upflow digester

Abstract: Domestic wastewater was fed continuously to a laboratory-scale upflow digester operated at short hydraulic retention times (HRT < 4 h). The digester acts as a system for sedimentation and hydrolysis of suspended solids (SS) and for acidification of solubi lised substances. Optimum results were obtained at an HRT of 2.3 h. Over 60% SS are retained in the digester and hydrolysed. Average influent SS content is 230 mg/l, whereas effluent SS is 90 mg/ l. Effluent SS concentrations shows very stable behaviour, varying little with influent concentration, as with HRT. Retention and hydrolysis of SS causes an increase in volatile fatty acid (VFA) concentration, from about 20 mg/l in the influent to above 100 mg/ l in the effluent, also contributing toward soluble fraction acidification. Thus, VFA reached 25% of effluent chemical oxygen demand (COD), while influent VFACOD was below 4%. During the process, a reduction in domestic wastewater COD of between 30 and 40% was observed.

A generalised solution for step-drawdown tests including flow dimension and elasticity

Abstract: Step-drawdown and multi-rate tests present convenient tools for the estimation of the long-term yield of boreholes. However, th e analytical methods commonly employed for the analysis of such tests are all based on the assumption that the drawdown in a borehole is a linear function of the discharge rate. Numerous constant rate tests, of which a few are discussed in this paper, has shown that this is not necessarily the case with boreholes drilled in the Karoo formations of South Africa. The drawdowns in these bo reholes are not only influenced by the peculiar geometry of the aquifers, but also the non-linear deformation of the aquifers during th e pumping of a borehole. The two new non-linear models for the analysis of step-drawdown and multi-rate tests introduced here, tr ies to account for these factors; in particular the deformation of the aquifer, flow dimension and dewatering of discrete fractures . Although the model proposed for multi-rate tests is still based on constant time steps, the one for step-drawdown tests allows the user to use arbitrary time steps, when performing the test in the field. Non-linearities in drawdown curves should always be treated with caution, especially when used to assign sustainable yields fo r boreholes. However, the example of a step-drawdown test performed at the Campus Test Site of the University of the Free State, shows that non-linearities can be addressed with an appropriate model.

Measurement of pH, alkalinity and acidity in ultra-soft waters

Abstract: Conventional characterisation of low alkalinity waters via pH measurement and titration of total alkalinity to a prescribed end-point invariably leads to large errors. These errors result from instability of the pH probe and an unknown titration end-point. In this paper two indirect methods (termed the "double Gran function" and the "blend" method) for the characterisation of such waters are evaluated critically. A blend composed of the raw water, sodium chloride (to increase conductivity), and standard bicarbonate (to increase buffering capacity) was titrated with standard strong acid in two pH regions: 6.3 pH WaterSA Vol.27(4) 2001: 423-432

Hydrological modelling of fine sediments in the Odzi River, Zimbabwe

Abstract: Siltation of reservoirs is a major concern in Zimbabwe. Therefore, development of prediction tools is of great importance. In t he present study a recently developed empirical sediment model (HBV-SED) based on a daily rainfall-runoff model was applied to simulate riverine fine sediment transport in a 2 486 km 2 catchment in eastern Zimbabwe. The model performance was evaluated and changes in the model structure were suggested. The modelling was, however, associated with many uncertainties due to the adopted simplification of transport processes. An analysis of the model structure and a comparison with the rating curve functi on was done. The required length of data for calibration purposes was evaluated and model validation through split sample and prox y basin comparison was performed. Furthermore, since the empirical model was dependent on monitored runoff and fine sediment concentrations for calibration purposes, a field measurement campaign was conducted to assess the accuracy of observed data at the station studied. The field measurements showed large errors in monitored runoff and fine sediment concentrations for the 19 98/ 99 wet season, which illustrated the uncertainty in predictions of fine sediment transport based on observed data. The HBV-SED model, which was applied over a period when data were believed to be fairly accurate, simulated the fine sediment transport vol ume well for the validation period if it was calibrated for a minimum of four years. A shorter calibration period led to a signific ant increase in prediction uncertainty. The model failed to simulate individual high fine sediment peaks accurately mainly due to poor performance of the rainfall-runoff model on a daily time-scale even if the seasonal flow dynamics were described properly. In t he studied catchment the HBV-SED model application resulted in equally poor R 2 -values as the rating curve technique, while the

Extending flood damage assessment methodology to include sociological and environmental dimensions

Abstract: Optimal and sustainable flood plain management, including flood control, can only be achieved when the impacts of flood control measures are considered for both the man-made and natural environments, and the sociological aspects are fully considered. Until now, methods/models developed to determine the influences of floods and flood control measures in South Africa, and elsewhere in the world, focus on the man-made environment and neglect the natural environment and social dimensions. Two models, recently completed in South Africa, namely FLODSIM (flood damage simulation model for irrigation areas) and TEWA (flood damage simulation model for urban areas) are cases in point. This paper gives an overview of the development of flood damage assessment and mitigation methodology in South Africa. Emphasis is placed on the evolution from the traditional ex-post approach to the latest ex-ante approach in which the sociological and natural environmental dimensions are included. Deliverables from the presentation should be of value to researchers and managers in the fields of flood management and environmental impact assessment worldwide. WaterSA Vol.27(4) 2001: 517-522

The hydrogeology of the Uitenhage Artesian Basin with reference to the Table Mountain Group Aquifer

Abstract: The Uitenhage Artesian Basin (UAB) lies in the Eastern Cape and is South Africa’s most important artesian groundwater basin, supplying approximately 1 400 Ml/yr (44 l/s) of water from springs for domestic use to Uitenhage, as well as supporting large citrus irrigation schemes. Groundwater from this basin has been extensively utilised from the early part of the 20 th century, including periods of over-exploitation resulting in the declaration of a groundwater control area to limit abstraction to sustainable rat es. The aquifer comprises fractured Table Mountain Group (TMG) sandstones confined in the eastern part of the basin by overlying Cretaceous siltstones and mudstones, resulting in artesian conditions. The Coega Fault is a major structural feature dividing the basin into separate systems, viz. the southern Swartkops Aquifer and the northern Coega Ridge Aquifer, that are hydrogeological ly independent of each other. The Elands River syncline divides the Swartkops Aquifer further into the Kruisrivier and Bethelsdor p Units. Borehole yields commonly range from 5 to 10 l/s and the groundwater quality is excellent with low salinities. Water hardening, however, is required due to the acidic and corrosive nature of the groundwater, typical of other Table Mountain Group aquifers in South Africa. Using 14 C data, the age of the groundwater in the basin ranges from 1 500 to 28 000 years with a calculated flow rate of 0.8 m/a. From the chloride mass balance method, recharge rates are determined to be 25 to 55% of annual rainfall. Groundwa ter temperatures generally show that depths of groundwater strikes do not necessarily correspond with depth of origin, indicating a complex groundwater circulation pattern within the basin. Whilst the UAB has been well studied locally, a basin-scale hydrogeological characterisation is considered to be necessary, followed by recommendations and formulation of a management plan to ensure the continued sustainability of groundwater supply from this national asset.

A baseline limnological study of Wagendrift Dam (Thukela basin, KwaZulu-Natal)

Abstract: Basic features of the physical and biological limnology of Wagendrift Dam, a moderately large impoundment on the Boesmans River, were studied between July 1989 and May 1990. This man-made lake showed a typical monomictic pattern of summer stratification (November through April) and holomictic winter circulation (May to October). Water quality was chemically good (Department of Water Affairs and Forestry records), with little evidence of nutrient enrichment. Water clarity during the stud y was moderately low (mean SD and K d PAR values of 0.45 m and 2.55 m -1 ), with little evidence of persistent mineral turbidity, suggesting reasonably satisfactory catchment conditions. In keeping with the low nutrient status, surface chlorophyll content remained be low 5 μg ·l - 1 throughout the study. In terms of ecological groupings, the phytoplankton was numerically dominated mostly by ‘Competitive’ green algae for most of the year. ‘Stress-tolerant’ cyanophytes were continuously sparse, but were marginally mo re abundant during summer stratification. Diatoms and other disturbance-tolerant ‘ruderal’ algae persisted throughout the year. No spring peak in ruderal algae was evident, but it may have been masked by high zooplankton grazing pressure. An autumnal peak in ruderal algae coincided broadly with flood-related inflows and annual de-stratification. Zooplankton was dominated (numerically and/or gravimetrically) by typical clear-water taxa. The copepod Tropodiaptomus spectabilis and cladoceran Daphnia pulex along with various unidentified cyclopoids and rotifers were seasonally persistent, while other cladoceran taxa (D. laevis and Diaphanosoma excisum) showed considerable seasonal periodicity. Zooplankton standing stock was collectively substantial, annually averaging around 0.65 g·m -2 DM, and approaching 1 g·m -2 DM in spring/early summer, implying potentially significant natural grazer-control of phytoplankton, aided perhaps by large numbers of benthic bivalve molluscs (Unio caffer), observed stranded in littoral margins following reservoir draw-down.

Installed water resource modelling systems for catchment management agencies

Abstract: Following international trends there are a growing number of modelling systems being installed for integrated water resource management, in Southern Africa. Such systems are likely to be installed for operational use in ongoing learning, research, stra tegic planning and consensus-building amongst stakeholders in the catchment management agencies (CMAs). These installed systems are poised to change fundamentally, the way modelling is approached in Southern Africa. They are a logical and irreversible response to the enormous forces which have led to the revision of the South African Water Law and the water resource management paradigms which it embodies. This paper examines the business forces behind this paradigm shift and it explores the evidence of the changes already taking place in terms of the modelling technology and the organisational and individual responses. Such installed modelling systems ar e essential for the social process of water allocation as well as for dealing with externalities. Given the paucity of observed data in Southern Africa, it follows that in many decision-making situations the model is not required to produce accurate answers, for we would have no way of checking their accuracy. Rather it is a tool to help organise a negotiation or learning process in which its primary function is to provide a framework for thinking by enabling the participan ts to make their implicit assumptions explicit in a systematic manner. This, in turn, provides a means for stakeholders to visit t he possible consequences of their intended actions. The creativity and opportunities for compromise which this process releases i s where the real benefit of modelling lies. Recurrent themes in this paper will be the business, technical and human resource issues pertaining to the use of installed modelling systems in the social process of water allocation.

Evaluation of detection methods for Legionella species using seeded water samples

Abstract: South African laboratories are currently using various methods in a non-standardised approach to detect Legionella species in environmental samples. In an attempt to provide guidelines for the development of a standard method, a number of currently available detection methods were evaluated, using seeded samples of sterile and non-sterile tap water, cooling water and make-u p water. The samples were seeded with a type strain of L. pneumophila serogroup 1 (American Type Culture Collection 33152). The effect of sample concentration by centrifugation and membrane filtration followed by either vortex or sonication for resuspensi on of organisms was studied. Three currently available culture methods were evaluated: the International standard method (ISO/DIS 11731), the Australian standard method (AS 3896 - 1991) and a locally-developed adaptation of the most probable number method (MPN). In addition, the direct immunofluorescence test and a commercially available latex agglutination test kit were included in the evaluations. The usefulness of treatment with acid or heat prior to culture was also compared. Our results indicated that concentration by membrane filtration using nitro-cellulose filters with a pore size of 0.45 μm, followed by sonication for 10 min, would be the most appropriate concentration and resuspension method for the samples. In the absence of sample pretreatment with acid or heat, organism recovery from sterile seeded samples on BCYE ranged from 85.9 ‐ 98.7%. However, in the non-sterile samples, these figures dropped to 8.1 ‐ 38.5%. Sample pretreatment resulted in a further loss of at least 50% of organisms in all the samples, regardless of the pretreatment method or culture medium used. In general, the ISO and AS methods were more appropriate than the MPN method for organism recovery from sterile seeded samples. However, for the nonsterile samples, the MPN method yielded better recovery.

Optimal water meter selection system

Abstract: The comparison of the particular accuracy envelope of a water meter with a consumer’s diurnal demand pattern by means of a common reference facilitates the optimal selection of water meters. The accuracy curve and envelope of a new water meter is governed by the type of water meter and relevant standards. Water demand patterns vary with time, period, seasons, consumers and combinations of these factors. The classical accuracy envelope and demand pattern are not directly comparable, and require a common comparison reference. The relative frequency of the volume of water passing through a meter at various flow rates and the weighted accuracies of these measured volumes play a pivotal rol e in establishing a common comparison reference. The time unit selected to calculate the volume of water passing through the meter is guided by the type of water reticulation infrastructure within which the meter is installed. However, experience and literature show that a flow interval of less than 1 min would result in the application of unrealistic high flow rates. A simplified example for the determination of the weighted accuracy of a water meter monitoring a theoretical demand pattern illustrates the methodology used to establish the common comparison reference. Economic/financial analysis based on an income statement together with capital budgeting techniques assist with the determination of the financial suitability of investing in a new replacement water meter. This financial analysis includes vari ous potential income and expenditure components that will result from the installation of a new water meter. Sensitivity analysis facilitates the decision-making process. The analysis of flow data by a computer program developed in context with the described methodology illustrates that the saving s achieved by the improved accuracy of matching the optimally selected meter and a particular demand profile can finance the cost s of such an investment.

Evaluation of short-term weather forecasts in South Africa

Abstract: In this paper a brief overview will be given for the reasons for doing evaluations of short-term weather forecasts as well as the methodology thereof. Short-term weather forecasts are defined as a forecast valid for the current day as well as the next day. In other words up to 48 h ahead. Results are given for South African Weather Service temperature, rainfall and severe weather forecasts as issued by head office in Pretoria. Temperature forecasts generally tend to be accurate to within a limit of 2.3°C. A comparison is made between temperature forecasts for an inland station, a coastal station and a station influenced by the escarpment. Tendencies of rainfall forecasts show that rain is forecast more often than it occurs. Comparative rainfall forecasts for a summer and winter rainfall region are shown. Severe weather events are sometimes captured well, but severe thunderstorms are not predicted with great accuracy. Once again the tendency is to over-forecast. With one of the scientific aims of forecasting evaluations being to concentrate on areas of under-performance, these statistics show that a better observation network would improve conditions for evaluation of forecasts. Further research should be focused on alternative or better techniques to forecast precipitation (general and severe)with greater accuracy. WaterSA Vol.27(4) 2001: 489-498

The analysis of 74 years of rainfall recorded by the Irwins on two farms south of Potchefstroom: technical note

Abstract: Rainfall records for three rain gauges on the farm Limerick and three rain gauges on the farm Mealielands were recorded from 19 24 until 1999 by Mr DJ Irwin and his son Mr NG Irwin The observations from these two nests of rain gauges are used to analyse the trends in rainfall measurements over time and to analyse the correlation of rainfall measurements between these rain gauges Th e results presented in this report highlight the fact that the observations of rainfall are different to one another in many case s, indicating that care should be taken when selecting a rain gauge to represent the rainfall over a particular area Analysis of the annual totals of rainfall has also found that at least 15 years of observations are required to determine a representative MAP value The ana lysis of the monthly rainfall data also indicates that the rainy season commences in November and ends towards the end of April A st udy of the extreme daily rainfall events shows that many of the storms are localised and are confined to an area around the rain ga uges The length of the droughts on these two farms are not as long as the national figures which would indicate that more point rain fall estimates are required to understand fully the spatial extent of a drought

Rationale for an ecological risk approach for South African water resource management

Abstract: The principle of ecosystem protection in the South African Water Act requires that water resource management tools for a multip le stressor environment be tailored to the characteristics of the aquatic ecosystem. The requirements of the Act, the characteris tics of aquatic ecosystems as well as co-occurrence of diverse stressors are considered. Although single substance criteria have a u seful role, they are not sufficient for resource management within the context of the ecological reserve. It is proposed that an effe ctlikelihood approach has the potential to address the variability and uncertainty in management of a surface water body subject to multiple stressors. An in-stream receiving water risk objective approach might be considered.

Utilisation of factorial experiments for the UV/H2O2 process in a batch reactor

Abstract: Factorial experiments provide a comprehensive understanding of the impact of operational variables on process performance. Utilisation of the Hadamard matrix taking into account all interaction effects, appeared to be efficient for giving a mathematical model that conformed to criteria validity. The predictions given by the factorial experiments model were confirmed by the experiments. Phenol oxidative degradation kinetics were not significantly influenced by pH or hardness of the solution to be treated, as is predicted by factorial experiments. On the other hand, initial H2O2 concentration, initial phenol concentration and temperature significantly influenced the efficiency of the process. Optimal values were determined: a temperature of about 20°C and a C H2O2 /C phenol ratio of 120 (mg/mg). WaterSA Vol.27(4) 2001: 551-558

An improved technique for the determination of oxidised nitrogen in natural waters with a Sequential Injection Analysis (SIA) system

Abstract: An SIA system is proposed for the determination of oxidised nitrogen (nitrate + nitrite as N) in natural waters. A cadmium red uctor, made of cadmium granules closely packed in a glass column reduces the nitrate to nitrite. The reduced nitrate and the nitrite present in the water samples is diazotised in the SIA system with sulphanilamide and coupled with N ‐ (1-napthyl) ethylene diammoniumdichloride to form a highly coloured azo dye which is detected at 540 nm with a UV/Vis spectrophotometer. The proposed system is fully computerised and is able to monitor total oxidised nitrogen as nitrite at a frequency of 36 samples pe r hour with a standard deviation of < 1.2%. The calibration curve is linear up to 5 mg/ l with a detection limit of 0.01 mg/ l.