Scielo RSS <![CDATA[Water SA]]> http://www.scielo.org.za/rss.php?pid=1816-795020110005&lang=en vol. 37 num. 5 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>Celebrating 40 years of achievement by the Water Research Commission</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502011000500001&lng=en&nrm=iso&tlng=en <![CDATA[<b>WRC 40-year Celebration Conference keynote address - the role of research and a knowledge-driven economy in development</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502011000500002&lng=en&nrm=iso&tlng=en <![CDATA[<b>WRC 40-year Celebration Conference - syntheses of themed sessions</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502011000500003&lng=en&nrm=iso&tlng=en <![CDATA[<b>WRC 40-year Celebration Conference concluding address - the Water Research Commission 40 years on</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502011000500004&lng=en&nrm=iso&tlng=en <![CDATA[<b>Approaches towards practical adaptive management options for selected water-related sectors in South Africa in a context of climate change</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502011000500005&lng=en&nrm=iso&tlng=en As a point of departure, the South African water-related sector is placed within the broader climate change context. Following on brief explanations of the terms adaptation, adaptive management and adaptive capacity, a summary of recent (2011) findings on projections of climate change effects on hydrological responses over South Africa is presented as the scientific cornerstone to practical adaptive management options. These options are based on the identification of major categories and subcategories in which adaptive capacity can be enhanced, the identification of 17 sectors within the broader South African water-related community which are likely to be impacted by climate change and the identification of the range of foreseen changes that these various sectors are likely to have to cope with, and adapt to, as a consequence of projected changes in climate drivers and hydrological responses. Five sectors are then selected for detailed case studies on adaptive management options, viz. national water planners, municipalities, rain-fed (dryland) agriculture, the insurance industry and aquatic ecosystems. The paper concludes by stressing the importance of adaptation to climate change and briefly outlines further plans of action in this field. <![CDATA[<b>Multi-scale climate modelling over Southern Africa using a variable-resolution global model</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502011000500006&lng=en&nrm=iso&tlng=en Evidence is provided of the successful application of a single atmospheric model code at time scales ranging from short-range weather forecasting through to projections of future climate change, and at spatial scales that vary from relatively low-resolution global simulations, to ultra-high resolution simulations at the micro-scale. The model used for these experiments is a variable-resolution global atmospheric model, the conformal-cubic atmospheric model (CCAM). It is shown that CCAM may be used to obtain plausible projections of future climate change, as well as skilful forecasts at the seasonal and short-range time scales, over the Southern African region. The model is additionally applied for extended simulations of present-day climate at spatial scales ranging from global simulations at relatively low horizontal resolution, to the micro-scale at ultra-high (1 km) resolution. Applying the atmospheric model at the shorter time scales provides the opportunity to test its physical parameterisation schemes and its response to fundamental forcing mechanisms (e.g. ENSO). The existing skill levels at the shorter time scales enhance the confidence in the model projections of future climate change, whilst the related verification studies indicate opportunities for future model improvement. <![CDATA[<b>Overview of water resource assessment in South Africa</b>: <b>current state and future challenges</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502011000500007&lng=en&nrm=iso&tlng=en This paper reviews the progress made in the assessment of water resources in South Africa over the past 60 years by examining 5 major studies that were undertaken in this period. These studies illustrate how the exponential growth in computer power and the concomitant development of highly sophisticated tools have changed the manner in which our water resources have been appraised, allowing us to deal with more and more complex issues, including: water quality, surface water/groundwater interaction and the reduction in runoff due to afforestation and alien vegetation. However, the main concern today is the serious decline in hydrological monitoring in recent times. It is imperative that this decline be addressed, especially if we are to deal effectively with problems related to climate cycles and climate change, together with the deterioration in water quality. <![CDATA[<b>Waters without borders</b>: <b>transboundary water governance and the role of the 'transdisciplinary individual' in Southern Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502011000500008&lng=en&nrm=iso&tlng=en Water resources in the Southern African Development Community (SADC) play an intrinsic role in regional development. As a result, water is a highly sensitive issue, complex to understand and demanding to govern, in terms of effective and equitable use and distribution. Growing awareness of the complex challenges facing water and the cross-cutting impacts that these challenges have on the region has led to the recognition that these challenges demand more integrated levels of ingenuity and expertise from a diverse set of actors working in a transdisciplinary manner. In response to these realisations a significant body of work has emerged that attempts to determine the criteria of a transdisciplinary approach and how it can be operationalised. This has led to significant progress in gaining an understanding of 'transdisciplinary team' approaches. These transdisciplinary teams have tended to work at the localised or project level of problem response. However, despite this progress, little work has been done on how to upscale transdisciplinary research and practice to the regional level. This is a significant gap given the fact that the source of many complex problems lies at the regional level even if the effects of these problems are localised. Also, little has been done to try to move the transdisciplinary discourse beyond the transdisciplinary team in order to understand how to groom and develop 'transdisciplinary individuals' who have the competence and talent to rise to the complex challenge of fostering regional economic development, of which water is a key component. Given this context, this paper builds on the existing literature in transdisciplinarity and its different conceptualisations in relation to water in Southern Africa. Firstly, it interrogates the cross-cutting role of water in regional socio-economic development in the SADC region. Secondly, it examines the need for transdisciplinary responses to regional socio-economic development. Thirdly, this paper strives to make a valuable contribution to knowledge in that it attempts to take the transdisciplinary discourse beyond 'the team' model to examine the role of the individual and the internalisation of transdisciplinarity as a mindset beyond collective models. In this regard, the paper emphasises the need for 'transdisciplinary individuals' to rise to the complex challenge of regional integration, and particularly, the role of the younger professionals in this process. <![CDATA[<b>Modelling the feasibility of retrofitting hydropower to existing South African dams</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502011000500009&lng=en&nrm=iso&tlng=en An investigation was carried out with the primary objective of ascertaining whether it is possible to develop a model for determining the feasibility of retrofitting hydropower to existing dams in South Africa. The need for such a model is primarily due to the growing importance of small-scale hydropower projects resulting from the global shift towards renewable energy and the South African energy crisis, the increased price of energy and the introduction of feed-in tariffs for renewables. The model is intended for engineers, typically working on behalf of a client who would like a simple first order assessment of feasibility. It therefore takes all technical, environmental, social and financial considerations into account in order to provide a recommendation on whether or not a project would be feasible. Achieving the primary objective required an in-depth study of the theory and literature related to the current electricity situation in South Africa as well as all the different components and considerations of hydropower projects. This theoretical knowledge could then be utilised to develop a computer model which combines the most important considerations into a cohesive whole in order to make a recommendation on feasibility. The accuracy and applicability of the model could then be ascertained through testing, using actual case studies in South Africa. Three test cases were utilised which yielded positive results. A number of difficulties were encountered. These related mainly to the development of an accurate means for pricing the different components primarily due to a lack of response from suppliers. Such issues were solved through the use of theoretical formulas and studies which provided good results. Ultimately, a model was developed which includes financial, environmental and social considerations and provides values that are accurate enough as an initial tool in determining whether or not to continue with a retrofitted hydropower project. <![CDATA[<b>Eutrophication</b>: <b>present reality and future challenges for South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502011000500010&lng=en&nrm=iso&tlng=en During the past 40 years, eutrophication has become an increasing threat to the usability of South African freshwater resources. Despite legislation moderating the discharge of phosphorus from some wastewater treatment works since the 1980s, eutrophication of freshwater resources is now widespread. Two important consequences are blooms of cyanobacteria, carrying the threat of cyanotoxin contamination, and excessive growth of macrophytes, which clog water-supply structures and reduce the recreational value of aquatic resources. Eutrophication-management options include reduction of phosphorus in detergents, biomanipulation of the food web, accurate prediction of cyanobacterial growth cycles, and mechanical disturbance of the epilimnion. The implementation of adaptive management to deal with eutrophication would ensure the testing and application of the most appropriate methodology to each eutrophic water body. Continued monitoring and reporting of trophic status are essential to establish whether interventions are having any effect. <![CDATA[<b>A review of the modelling of water values in different use sectors in South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502011000500011&lng=en&nrm=iso&tlng=en In this article several economic studies undertaken to assist with the implementation of the National Water Act (NWA) No. 36 of 1998 are reviewed. In these studies the following procedures were applied to model water use: operational research, econometric analysis, input/output analysis, willingness to pay and the conceptual framework of water markets. Main use sectors are agriculture, forestry, municipalities (domestic consumption) and the environment. Water values estimated in the studies differ significantly between sectors, as well as between and within catchment areas. Most of the studies focused on irrigated agriculture as an important use sector in terms of water volumes, food production and capital investment. Input/ output analysis indicates that South African agriculture is a less productive user of water in terms of gross income generated per unit of water. Evidence suggests that industrial and domestic use place a high value on assurance of supply of current water consumption levels. In contrast, agriculture requires large volumes of water for food production in response to market demand. The average value product of water is much higher for industry than agriculture, but the marginal value products appear similar in both sectors. From this it is concluded that water-use rights will in future be transferred from agriculture to industry but there is no urgency at present. As water is transferred in future from agriculture to domestic use and industrial use, the value (rents) now attached to land will transfer to water and real water prices will accordingly increase. The transfer of rents from land to water should not affect the value of farms. The expected significant increase in real water prices in a water market will provide further incentives for its conservation. The purpose in this review paper that covers a wide range of topics is to provide information to policy decision-makers on the economics of water management in South Africa. <![CDATA[<b>The recreational value of river inflows into South African estuaries</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502011000500012&lng=en&nrm=iso&tlng=en Estuarine habitats are subject to increasing demand pressures. Some of these are direct, for the appealing space they provide for residences and recreation; and some are indirect, in the form of competitive demand for the inputs required to maintain their ecological functionality, for instance, river inflows. As a result of increasing demand for river water the connection of many of South Africa's estuaries with the sea has been undermined and their recreational appeal reduced. This paper reports findings on these negative impacts for selected estuaries. The contingent valuation method was used to estimate the value of recreational benefits that would result at 40 South African estuaries if water-inflow reductions were averted. The studies were undertaken between 2000 and 2007. All the estuaries selected were known to be vulnerable to changes in river inflows. Expert opinions on the consequences of specified hypothetical changes to water inflows into estuaries were used to generate the scenarios valued. User populations were estimated and surveys administered to samples of these populations. From the elicited responses median estuary user willingness to pay bids were predicted using Tobit and OLS models. An internal credibility assessment was conducted over the plausibility of the predictive model, the consistency of the values to those estimated using an alternative valuation method (the contingent travel cost method), and the reliability of the estimates. For the 37 estimates deemed reliable (but not necessarily valid), the average of the predicted median values of river inflow into estuaries was calculated to be 3.4 c/m³ (South African cents, ZAR) and standard deviation 3.84 c/m³. The average of the predicted mean values was calculated to be 7.4 c/m³ and the standard deviation 6.7 c/m³. It was also found that where there had been extensive economic development around the river system, the values of inflows into estuaries tended to be less than the value of water abstracted upstream. <![CDATA[<b>Life-cycle assessments in the South African water sector</b>: <b>a review and future challenges</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502011000500013&lng=en&nrm=iso&tlng=en This paper reviews South African water sector life-cycle assessments (LCAs) and develops a position on how this tool could be strategically employed in the future. It summarises the studies undertaken, highlighting the significant findings and the lessons learnt. In addition, international trends and their implications for the local LCA community and the water sector are presented and strategic recommendations for the future are included. The various LCA studies undertaken in the local water industry have shown that the abstraction of water from the environment (in a country where it is a limited resource) and the use of energy for treating and pumping water and wastewater have the highest environmental burdens. These studies have also demonstrated the versatility of LCA as a decision-making tool in the water industry by comparing technologies and scenarios, identifying improvement opportunities and prioritising interventions and their consequences in complex water systems. Recent international work has confirmed the usefulness of a life-cycle approach also for water footprinting. Therefore, in South Africa it is important to promote the use of LCAs for the water sector in order to improve efficiency of processes and systems, but also to promote life-cycle based water footprinting and to include differentiated water consump tion data into life-cycle inventories to make more efficient use of water as a resource. <![CDATA[<b>Development of guidance for sustainable irrigation use of greywater in gardens and small-scale agriculture in South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502011000500014&lng=en&nrm=iso&tlng=en Greywater is untreated household effluent from baths, showers, kitchen and hand-wash basins and laundry (i.e. all non-toilet uses). More than half of indoor household water is normally used for these purposes and can potentially be intercepted by the householder for additional beneficial uses. Greywater use is practised on an informal basis to supplement irrigation water, either in urban gardens in middle- to upper-income suburbs or in food gardens in lower-income informal, peri urban and rural areas. It holds the potential to contribute significantly to food security in poor settlements by providing a source of both irrigation water and nutrients for crop plants. However, there are presently no formal guidelines for the use of greywater in South Africa. This paper presents the rationale and framework of a guidance document for the sustainable use of greywater to irrigate gardens and small-scale agriculture in South Africa, developed under the auspices of the Water Research Commission. The 3 driving principles in developing this guidance were: protection of human health; protection of plants irrigated; and protection of soil and the environment. Risk-management scenarios were developed on the basis of the extent of greywater characterisation. Water-quality constituents for inclusion were selected from among those indicated as presenting a problem in previous studies. Guidance was provided for managing greywater quality, either by mitigation of greywater quality (by practices such as irrigation method, amelioration of soil, leaching of soil and planting of tolerant plant types) or by small-scale biological treatment of greywater. Guidance was also given regarding the volumes of greywater which can be applied, together with factors to adjust these volumes for site-specific conditions. <![CDATA[<b>Case studies from Water Research Commission projects along the Lower Vaal, Riet, Berg and Breede Rivers</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502011000500015&lng=en&nrm=iso&tlng=en A vast number of projects on salinity in irrigated agriculture were funded by the Water Research Commission (WRC) during the past 40 years. However, due to the diversity of the projects it is virtually impossible to cover all aspects thoroughly in a paper of limited length. Thus this review focuses mainly on projects along the Lower Vaal, Riet, Berg and Breede Rivers in South Africa. The results on the water quality of these rivers indicate that irrigation has led to the deterioration of water sources. There is a direct relationship between river water quality and soils irrigated. Fortunately, effective land-suitability guidelines were developed and applied during the establishment of the major irrigation schemes. This facilitated the management of soils under irrigation. The results from long-term irrigation case studies along the Lower Vaal River and Breede River show that the quality of soils can be improved. The opposite is also true where mismanagement occurred. Research on the salinity threshold of major crops (grapevines, wheat, maize, groundnuts, etc.) confirmed the empiric nature of the guidelines. It is suggested that a more dynamic approach be used for managing salinity under irrigation at farm level, i.e. the use of models. Amongst others, future research should focus on determining the spatial and temporal distribution of salt in irrigated soils. <![CDATA[<b>Irrigation scheduling research</b>: <b>South African experiences and future prospects</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502011000500016&lng=en&nrm=iso&tlng=en Many scheduling approaches have been developed with Water Research Commission funding over the past 4 decades and deployed with varying levels of success; 2 approaches have won prestigious international awards. Soil-based approaches which include measurement of matric potential (tensiometry), water content (neutron probes, capacitance sensors) and depth of wetting (wetting front detectors) have been relatively well accepted by farmers. Atmospheric-based approaches apply, through biophysical modelling of the soil-crop-atmosphere system, thermodynamic limits to the amount of water that can evaporate from a cropped surface under particular environmental conditions. Modelling approaches have been quite empiri cal or somewhat more mechanistic, generic or crop specific, with pre-programmed (e.g. irrigation calendars) or real-time output. Novel mechanisms have been developed to deliver recommendations to farmers, including resource-poor irrigators. Although general adoption of objective irrigation scheduling in South Africa is still low, the high cost of electricity and nitrogen, and scarcity of water is reviving the interest of consultants and irrigators in the application of these tools to use water more efficiently. Where adoption has been relatively high, intensive support and farmer-researcher-consultant interactions have been key contributing factors. We propose 4 avenues in the R&D domain to ensure responsible water utilisation. Firstly, there is a need to continue to advance existing soil-water measurement technology; and secondly, to further develop new and emerging technologies, like the use of remote sensing. Thirdly, the user-friendliness should be improved as should systems that support existing scheduling tools; and finally, we need to appreciate that farmers are intuitively adaptive managers, and we need to develop simple monitoring tools and conceptual frameworks that enable structured learning. <![CDATA[<b>Irrigation methods for efficient water application</b>: <b>40 years of South African research excellence</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502011000500017&lng=en&nrm=iso&tlng=en The purpose of an irrigation system is to apply the desired amount of water, at the correct application rate and uniformly to the whole field, at the right time, with the least amount of non-beneficial water consumption (losses), and as economically as possible. We know that irrigated agriculture plays a major role in the livelihoods of nations all over the world and South Africa is no exception. With the agricultural water-use sector being the largest of all water-use sectors in South Africa, there have been increased expectations that the sector should increase efficiency and reduce consumption in order to increase the amount of water available for other uses. Studies and research over 40 years, on the techniques of flood-, mobile- and micro-irrigation have contributed to the knowledge base of applying irrigation methods correctly. In a recent study on irrigation efficiency, the approach is that irrigation efficiency should be assessed by applying a water balance to a specific situation rather than by calculating various performance indicators. The fraction of the water abstracted from the source that is utilised by the plant is called the beneficial water-use component, and optimised irrigation water supply is therefore aimed at maximising this component. It implies that water must be delivered from the source to the field both efficiently and effectively. Optimising water use at farm level requires careful consideration of the implications of decisions made during both development (planning and design), and management (operation and maintenance), taking into account technical, economic and environmental issues. An exciting, newly-developed South African Framework for Improved Efficiency of Irrigation Water Use covers 4 levels of water-management infrastructure: the water source, bulk conveyance system, the irrigation scheme and the irrigation farm. The water-balance approach can be applied at any level, within defined boundaries, or across all levels to assess performance within the entire water management area. <![CDATA[<b>Review of 'plant available water' aspects of water use efficiency under irrigated and dryland conditions</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502011000500018&lng=en&nrm=iso&tlng=en This review provides an overview of Water Research Commission (WRC)-funded research over the past 36 years. A total of 28 WRC reports have been consulted, 13 of these compiled by the University of the Free State, 4 by the University of Fort Hare, and the remainder mainly by the ARC-Institute for Soil Climate and Water. This work has resulted in extensive capacity building in this field - numerous technical assistants and 58 researchers have been involved, of which 23 are still active in research. The focus on the water flow processes in the soil-plant-atmosphere continuum (SPAC), with particular emphasis on processes in the soil, has greatly enhanced understanding of the system, thereby enabling the formulation of a quantitative model relating the water supply from a layered soil profile to water demand; the formulation of logical quantitative definitions for crop-ecotope specific upper and lower limits of available water; the identification of the harmful rootzone development effects of compacted layers in fine sandy soils caused by cultivation, and amelioration procedures to prevent these effects; and management strategies to combat excessive water losses by deep drainage. The explanation of the way in which SPAC is expressed in the landscape in the form of the ecotope has been beneficial with regard to the extrapolation of studies on particular SPACs to the large number of ecotopes where detailed studies have not been possible. Valuable results are reported regarding rainfall and runoff management strategies. Longer fallow periods and deficit irrigation on certain crop ecotopes improved rainfall use efficiency. On semi-arid ecotopes with high-drought-risk clay and duplex soils and high runoff losses, in-field rainwater harvesting (IRWH), designed specifically for subsistence farmers, resulted in maize and sunflower yield increases of between 30% and 50% compared to yields obtained with conventional tillage. An indication of the level of understanding of the relevant processes that has been achieved is demonstrated by their quantitative description in mathematical and empirical models: BEWAB for irrigation, SWAMP mainly for dryland cropping, and CYP-SA for IRWH. Five important related research and development needs are identified. The WRC has played, and continues to play, an important role in commissioning and funding research on water utilisation in agriculture and has clearly made an excellent contribution to the progress made in addressing the needs and requirements of subsistence, emergent and dryland farmers in South Africa. <![CDATA[<b>Water use of grasslands, agroforestry systems and indigenous forests</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502011000500019&lng=en&nrm=iso&tlng=en The biotic and abiotic components of ecosystems affect each other through complex interactions and processes. These dynamic interactions give ecosystems their distinct identities and provide ecosystem services critical to human survival (e.g. water, energy and nutrients). However, human activities (e.g. commercial forestry, agriculture) have placed increasing demands on specific ecosystem services. The effect of these activities on ecosystem processes has been the focus of numerous Water Research Commission (WRC) studies. Some of these have determined man's impact on plant-water use, biomass production (energy) and water use efficiency (biomass produced per unit of water transpired, termed productive green-water use). For example, measurements of evapotranspiration (ETa) from different vegetation types showed that annual water use is strongly related to the proportion of the year in which a dense canopy of transpiring leaves is maintained. Thus, evergreen vegetation such as riparian fynbos and plantations of introduced tree species exhibit a relatively high annual ETa, when compared to seasonal grasslands and deciduous trees that only maintain their transpiring canopy during sum mer. Quantification of the annual volumes of water used by these different vegetation types, under differing climatic and site conditions, has been possible through these studies. At a stand scale, measurements of the different components of evapotranspiration have allowed the partitioning of beneficial (transpiration) and non-beneficial (evaporation) fluxes. At a catchment scale measurements have quantified the proportional allocation of water to the different components of the water balance. Three case studies are presented to illustrate this. In a stand of Jatropha curcas, measurements of daily total evaporation rates during December to February (summer) on clear hot days ranged between 3 mm·d-1 to 4 mm·d-1. However, due to the deciduous nature of the species, water use was negligible (< 1 mm·d-1) during winter (May to August). At a catchment scale, studies in a montane grassland ecosystem of the KwaZulu-Natal Drakensberg showed that the partitioning of the main hydrological fluxes into streamflow and evaporation was dependent on the wetness of the hydrological year. In average to wet years (>1 200 mm precipitation) the hydrological flux was equally split between evaporation (650 mm) and runoff (550 mm), while in drier years evaporation became the dominating component of the water balance (752 mm vs. 356 mm, respectively). The data provided an important baseline for comparison with other impacted ecosystems (especially commercial forestry). Finally, results of a variety of studies on the growth and water use of indigenous trees growing in natural forest and plantation systems suggest that, compared to introduced tree species, indigenous species use substantially less water, show lower water use efficiency, and grow more slowly. Advantages to such indigenous systems potentially include lower management costs, higher product values, a wider range of non-wood products and a lower hydrological impact. Their usefulness may be greatest on sensitive sites (e.g. riparian zones, water-stressed catchments, land cleared of alien plants, land with a high erosion risk, degraded forest) where land use systems with a reduced environmental impact are required. <![CDATA[<b>Review of whole-farm economic modelling for irrigation farming</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502011000500020&lng=en&nrm=iso&tlng=en The main objective of this paper is to review the progress that has been made in South Africa with respect to whole-farm economic modelling over the past 2 decades. Farming systems are complex and careful consideration to the stochastic dynamic nature of irrigation farming processes and their linkages with the larger water system is necessary when conducting whole-farm modelling. Both simulation and optimisation approaches to whole-farm modelling have been developed. Simulation is able to realistically model key performance indicators for decision-making while taking cognisance of the stochastic dynamic nature of irrigation agriculture. Normally only a few predefined scenarios are considered and these do not include decisions regarding allocation of water between competing farm uses of water. Optimisation models take the opportunity cost of water into account while optimising water use between multiple crops. Simplifications of the soil-crop-water subsystem are necessary to optimise agricultural water use between activities which are differentiated by crop, irrigation technology and soil at whole-farm level. Appropriate use of crop simulation models to provide input for mathematical programming models holds promise but needs to be weighed against the extra time needed to validate models and generate the required information. Research is necessary to determine the value of considering water as a stock resource compared to a situation where water use is optimised without considering water as a stock resource. Optimisation results indicated that it is profitable to irrigate larger areas with water saved from deficit irrigation and increasing irrigation efficiency. Relatively little research was done to demonstrate the externalities caused by irrigation farming under the current water policy. Future research should focus on developing integrated hydro-economic modelling frameworks that will incorporate irrigation externalities. Modelling decision-making by means of a single-attribute utility function is unsatisfactory and more research is necessary to improve understanding of the decision-making process to enhance whole-farm modelling frameworks that will assist farmers in making tactical decisions. <![CDATA[<b>Smallholder irrigation schemes in South Africa</b>: <b>a review of knowledge generated by the Water Research Commission</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502011000500021&lng=en&nrm=iso&tlng=en The status and characteristics of the 302 smallholder irrigation schemes found in South Africa are discussed and knowledge on South African smallholder irrigation schemes generated by the Water Research Commission (WRC) over a period of nearly 20 years is reviewed. Themes covered include planning, design and technology; plot-holders and their livelihoods; institutions and organisations; support services; agronomic practices; and revitalisation. The availability of guidelines on most of these aspects is highlighted. Gaps in the knowledge of social, human and economic aspects of smallholder irrigation schemes are pointed out.