Environmental Hydrology

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Development of a framework for an integrated time-varying agrohydrological forecast system for southern Africa.
(2007) Ghile, Yonas Beyene.; Schulze, Roland Edgar.
Policy makers, water managers, farmers and many other sectors of the society in southern Africa are confronting increasingly complex decisions as a result of the marked day-to-day, intra-seasonal and inter-annual variability of climate. Hence, forecasts of hydro-climatic variables with lead times of days to seasons ahead are becoming increasingly important to them in making more informed risk-based management decisions. With improved representations of atmospheric processes and advances in computer technology, a major improvement has been made by institutions such as the South African Weather Service, the University of Pretoria and the University of Cape Town in forecasting southern Africa’s weather at short lead times and its various climatic statistics for longer time ranges. In spite of these improvements, the operational utility of weather and climate forecasts, especially in agricultural and water management decision making, is still limited. This is so mainly because of a lack of reliability in their accuracy and the fact that they are not suited directly to the requirements of agrohydrological models with respect to their spatial and temporal scales and formats. As a result, the need has arisen to develop a GIS based framework in which the “translation” of weather and climate forecasts into more tangible agrohydrological forecasts such as streamflows, reservoir levels or crop yields is facilitated for enhanced economic, environmental and societal decision making over southern Africa in general, and in selected catchments in particular. This study focuses on the development of such a framework. As a precursor to describing and evaluating this framework, however, one important objective was to review the potential impacts of climate variability on water resources and agriculture, as well as assessing current approaches to managing climate variability and minimising risks from a hydrological perspective. With the aim of understanding the broad range of forecasting systems, the review was extended to the current state of hydro-climatic forecasting techniques and their potential applications in order to reduce vulnerability in the management of water resources and agricultural systems. This was followed by a brief review of some challenges and approaches to maximising benefits from these hydro-climatic forecasts. A GIS based framework has been developed to serve as an aid to process all the computations required to translate near real time rainfall fields estimated by remotely sensed tools, as well as daily rainfall forecasts with a range of lead times provided by Numerical Weather Prediction (NWP) models into daily quantitative values which are suitable for application with hydrological or crop models. Another major component of the framework was the development of two methodologies, viz. the Historical Sequence Method and the Ensemble Re-ordering Based Method for the translation of a triplet of categorical monthly and seasonal rainfall forecasts (i.e. Above, Near and Below Normal) into daily quantitative values, as such a triplet of probabilities cannot be applied in its original published form into hydrological/crop models which operate on a daily time step. The outputs of various near real time observations, of weather and climate models, as well as of downscaling methodologies were evaluated against observations in the Mgeni catchment in KwaZulu-Natal, South Africa, both in terms of rainfall characteristics as well as of streamflows simulated with the daily time step ACRU model. A comparative study of rainfall derived from daily reporting raingauges, ground based radars, satellites and merged fields indicated that the raingauge and merged rainfall fields displayed relatively realistic results and they may be used to simulate the “now state” of a catchment at the beginning of a forecast period. The performance of three NWP models, viz. the C-CAM, UM and NCEP-MRF, were found to vary from one event to another. However, the C-CAM model showed a general tendency of under-estimation whereas the UM and NCEP-MRF models suffered from significant over-estimation of the summer rainfall over the Mgeni catchment. Ensembles of simulated streamflows with the ACRU model using ensembles of rainfalls derived from both the Historical Sequence Method and the Ensemble Re-ordering Based Method showed reasonably good results for most of the selected months and seasons for which they were tested, which indicates that the two methods of transforming categorical seasonal forecasts into ensembles of daily quantitative rainfall values are useful for various agrohydrological applications in South Africa and possibly elsewhere. The use of the Ensemble Re-ordering Based Method was also found to be quite effective in generating the transitional probabilities of rain days and dry days as well as the persistence of dry and wet spells within forecast cycles, all of which are important in the evaluation and forecasting of streamflows and crop yields, as well as droughts and floods. Finally, future areas of research which could facilitate the practical implementation of the framework were identified.
Understanding agricultural innovation adoption processes and garden scale water use through farmer-driven experimentation
(2008) Sturdy, Jody D.
A holistic approach to agricultural innovation development and extension is needed to
Rainwater harvesting systems and their influences on field scale soil hydraulic properties, water fluxes and crop production.
(2009) Kosgei, Job Rotich.; Jewitt, Graham Paul Wyndham.; Lorentz, Simon Antony.
South Africa, in common with many parts of Sub-Saharan Africa, is facing increasing water shortages. Limited available water arising from a low and poorly distributed rainfall, must supply domestic, agricultural, industrial and ecosystem needs. Agricultural activities of smallholder farmers, who largely occupy arid to semi-arid areas, are rainfall-driven as they do not have the capacity to develop conventional water sources, such as boreholes and large dams. This situation has led to persistent food shortages, low income and a lack of investments, resulting in high dependency levels of which examples include over reliance on social grants, household crop production that largely relies on external inputs and availability of cheap unskilled labour. A growing global perception that water for agriculture has low value relative to other value uses could further jeopardize the already over exploited agricultural water. Developing economies such as South Africa are likely to favour, in terms of water allocation, e.g. electricity generation through steam turbines relative to irrigation needs because industry plays a more significant role in the economy. While substantial scientific research has resulted in enhanced yields through in-situ water harvesting and soil and water conservation, as well as crop and soil fertility management and plant breeding, less work has been done to assess the impact of intermittent dry spells on crop yield, particularly with regard to smallholders. Indeed, the interventions that have been promoted to smallholders may provide little buffer against such events. In addition, the increase in yield from many such efforts has been marginal and inconsistent, leading some to conclude that semi-arid environments are hydrologically marginal, have no significant agricultural potential and any attempts to intensify agricultural activities would lead to severe environmental degradation. This study investigated the rainwater harvesting and storage potential among rainfed farmers in a summer-rainfall region of South Africa. The influences of this practice on soil hydraulic properties, water fluxes and crop production is detailed in subsequent chapters. Using historical meteorological data, this study commenced with an investigation of the factors that influence the length of maize (Zea Mays L.) growing seasons notably the prevalence of early season dry spells and late season low temperature which could be responsible for persistent low maize yields amongst smallholder rainfed farmers (Chapter 2). An increasing trend of dry spells was observed which was found to influence sowing dates and the length of the growing season. The influence of no-tillage (NT) as an intervention to secure more root-zone soil moisture was investigated in comparison to conventional tillage (CT) practices. Field experiments, with the aim of quantifying the extent to which water productivity and yields can be improved among smallholder rainfed farmers in the Potshini catchment, Thukela basin; South Africa (Chapter 8), were conducted during both the dry and growing seasons from 2005/06 – 2007/08 seasons at four sites with similar soil textural properties and slopes. Each site was developed as a runoff plot and was fitted with moisture and runoff measuring devices. Meteorological parameters were measured from a weather station installed nearby. A snapshot electrical resistivity survey was used to compliment soil moisture profiling. The analyses of the different measurements provided information on various water flow paths and potential downstream hydrological effects (Chapter 3). The average cumulative runoff was 7% and 9% of seasonal rainfall in NT and CT treatments over the three seasons. Changes over time in soil hydraulic properties due to tillage were examined at two depths through infiltration tests and determination of their bulk densities. These included changes in steady state infiltration rate and hydraulic conductivity (Chapter 4), interaction between soil infiltration and soil characteristics (Chapter 5) and water conducting porosity and water retention (Chapter 6). In 50% of the sites, NT treatments showed significantly higher hydraulic conductivity compared to CT treatments. In response to an unexploited opportunity identified to produce vegetables in winter, an assessment of the potential for runoff water harvesting systems using polyethylene lining as an alternative cost-effective construction method for underground rainwater storage systems, particularly in areas where groundwater levels fluctuate rapidly was undertaken (Chapter 7). The process from conceptualization through design, construction and utilization of the stored water is described and recommendations for the design and construction of such systems made. Finally, various case studies which highlight the potential impact of improved soil profile moisture storage, the additional benefits of water stored in tanks and recommendations for tailored policies to support household food and income generation are made (Chapter 8).
The feasibility of automatic on-board weighing systems in the South African sugarcane transport industry.
(2009) Pletts, T. R.; Lyne, Peter William Liversedge.; Lagrange, Louis F.
Sugarcane hauliers in South Africa have high variations in vehicle payloads, which influence both transport economics and the legitimacy of their operations. Increasing economic pressure due to declining sugar prices and ever increasing fuel prices has invoked interest to improve vehicle utilisation and reduce costs, while complying with the local traffic legislation. On-board weighing technologies, such as on-board load cells, could assist operators to control their payloads more accurately and hence reduce the frequency of both over and under loaded consignments. In this study, an investigation is conducted to evaluate the feasibility of on-board weighing systems in the South African sugarcane transport industry. An overview of on-board weighing systems is presented. The overview gives insight into the technical composition of an on-board weighing system as well as presenting various benefits and drawbacks that are associated with an on-board weighing system. Earlier studies conducted on the use of on-board weighing systems are scrutinised and evaluated and it is concluded from these that vehicle utilisation could be improved, while concurrently reducing the overloading of vehicles. Field research was conducted to evaluate the accuracy and consistency of on-board weighing systems currently being utilised in the sugarcane transport industry as well as to determine the critical factors that influence the effectiveness of the system while assessing if overloading of vehicles was reduced when on-board weighing systems were employed. It was concluded that the systems evaluated were reasonably accurate with mean error being 0.4 tons. The consistency of the systems was good with 75% of all measurement being within 0.5 tons of each other. The critical factors determining the effectiveness of the on-board weighing systems were established as being management of the system as well as cane variety and quality. Overloading was reduced by 9% in one field evaluation and 5% in another. Further reduction can be realised through tighter management of the on-board weighing systems. An economic evaluation of an on-board weighing system was performed using the capital budget method. This method was used to determine the pay off period required to realise the investment into an on-board weighing system for scenarios where the payload is increased by 2, 3 and 4 tons and transport lead distance is 20, 40, 60, 80, and 100 km. The shortest pay off period occurred when the lead distance was 60 km and the time was 1, 2 and 3 years for payload increases of 2, 3 and 4 tons respectively. For lead distances of 40, 60 and 80 km the investment is worthwhile and considerable returns in investment can be realised, however, for the other lead distances the pay off period could be deemed to be too long. From the observation made during the field evaluation together with the literature studied, guidelines for the use of on-board weighing systems under various transport scenarios were formulated and are presented in chapter six.
A framework to improve irrigation design and operating strategies in the South African sugarcane industry.
(2009) Jumman, Ashiel.; Senzanje, Aidan.; Lecler, Neil Louis.
The purpose of this study was to develop a framework to assess irrigation design and operating strategies. This objective was achieved successfully and the framework was applied to formulate guidelines to increase farm profitability whilst using scarce resources, such as water and electricity, effectively. The study was targeted at sugarcane irrigated with semi-permanent irrigation systems. “ZIMsched 2.0”, a water balance and crop yield prediction model and the “Irriecon V2” economic assessment model were available at the start of the study. The missing link, however, was a relatively cost effective and efficient method to design and cost irrigation hardware alternatives. Irrigation hardware impacts on both the agronomic and economic performance of systems, for example, through different peak design capacities and associated operating limitations. Thus, a novel, spreadsheet-based irrigation design tool, with an automated costing component, was developed to complete the framework. The framework was used to investigate the costs and benefits of potential design and operating solutions to a selection of irrigation issues, including: over-irrigation on shallow soils, the opportunity to shift electricity use out of expensive peak periods and, the opportunity to demonstrate the benefits of deficit irrigation strategies. For shallow soils, the increase in system hardware costs, needed to better match water application to soils, increased margins due to more effective water use. Innovative deficit designs and operating strategies allowed for reductions in water and electricity costs. The reduced costs, however, did not always offset yield penalties and revenue loss resulting from water stress. The financial benefits of deficit irrigation strategies were shown when water savings were used to convert dry land cane into irrigated cane. This highlighted the differences between the direct and opportunity costs of water. Finally, a field work component, relating to the precise monitoring of irrigation strategies and corresponding crop responses was included in this study. Systems which enabled soil water potential and stalk extension to be monitored remotely via the internet were considered useful for the successful implementation of an optimum irrigation strategy. The easily accessible data allows for effective decision making and more importantly, reassures famers of the current state of their crop.
The impacts of woody invasive alien plants on stream hydrogeomorphology in small headwater streams of KwaZulu-Natal.
(2010) Bruton, Simon N.; Jewitt, Graham Paul Wyndham.
South Africa has a long history of problems with invasive alien species. In an assessment of alien invading plants and water resources in South Africa Versveld et al. (1998) estimated that Invasive Alien Plants (IAPs) in South Africa covered an area equivalent to the size of KwaZulu-Natal. However this area of invasion was primarily concentrated along the river courses of South Africa as alien invasions are arguably a riparian problem (Versveld et al., 1998). In a 1998 assessment of the distribution of IAPs in South Africa Versveld et al. (1998) found a total invasion extent of 8% for South Africa (including Lesotho), while KwaZulu-Natal had a higher total extent of invasion at 9.75%. However the authors noted the limitations of the IAP mapping assessment and stated that from personal observations and observers’ comments the area invaded by IAPs may be as much as 2-3 times greater than the 9.75% value obtained for KwaZulu-Natal. South Africa’s most widespread invasive alien tree (Dye and Jarmain, 2004), Acacia mearnsii (black wattle), is ubiquitous throughout KwaZulu-Natal, and invades most severely where water is plentiful, such as along watercourses and road verges. However following dispersal along rivers, A. mearnsii spreads into adjacent terrestrial habitats (Richardson and Kluge, 2008) including indigenous grassland and forest. A. mearnsii was introduced to South Africa in the middle 19th century to provide tanbark, woodchips, construction poles and firewood, and its introduction spread rapidly across KwaZulu-Natal through farmers and foresters (Henderson, 2001; WESSA, 2008). River and riparian zone rehabilitation is becoming accepted as having an essential role to play in the long term solution of water resource quality and supply problems and environmental health as a whole. As a result the impact of IAP invasions on water resources, ecological habitats and the delivery of ecosystem goods and services has undergone much scientific investigation (van Wilgen et al., 2008). Numerous studies have shown that, under most circumstances, removal of IAPs results in a general increase in streamflow and returns a stream to a more natural seasonal flow regime. However, scientific studies on the influences of woody IAPs on the hydrogeomorphology of riparian areas, and the resultant effects on stream hydrology and ecology, have undergone little scientific investigation in the South African context. Hydrogeomorphology studies the linkages of surface and subsurface water, and hydrological processes with landforms and geomorphic processes in temporal and spatial dimensions. As a result the discipline is well applied to the study of the interaction of, and interdisciplinary impacts of IAPs on riparian areas. Macdonald (2004:22) stated that there is a need to “investigate the interaction of IAPs with other aspects of water quality, for example soil erosion rates, including river channel and bank erosion.” In the early 1990s, after a study assessing the potential impact of IAPs on the geomorphology of river channels in South Africa, Rowntree (1991) stressed that further research on the influence of IAPs on stream geomorphology is required to guide truly effective riparian zone management. Since this study, little scientific work has been undertaken on this topic in the South African context. The literature review portion of this dissertation reviews the findings of various researchers as to how IAPs physically influence riparian habitats, specifically with reference to the role of IAPs in degrading riparian and streambank landscapes to an extent that streambank stability and stream channel form is adversely affected. This topic is introduced by illustrating the many functions that riparian zones can perform and some of the possible consequences of a loss of riparian habitat integrity. Worldwide awareness of the functions and values of riparian systems has led many countries to perform inventories of threatened and valuable riparian areas. A database of stream habitat integrity is useful for environmental impact assessments, development planning and resource inventories. Thus a multitude of stream survey and aquatic health sampling techniques and methodologies have been developed, some of which could be applied to assessing the influence of IAPs on riparian zones. 1.1 Research Aims and Objectives This dissertation forms a research study based on field research centred around field methods and tools developed after a review of relevant literature. The key aims of this research study are to; · refine an international river habitat survey method for application within South Africa, and · develop a test case to implement the developed method in analysing the impacts of IAPs on stream hydrogeomorphology in small headwater streams of KwaZulu-Natal, South Africa. These aims are achieved through the following objectives; · investigate the current body of knowledge covering the impact of woody IAP invasions on streambank stability and channel form, · review available stream survey methods and develop a stream survey methodology which can be applied to investigate the relationships between woody IAP invasions and streambank stability and form within headwater streams of KwaZulu-Natal, · investigate the relationships illustrated by the data after applying the developed stream survey tools and fieldwork methodology, and · discuss any shortfalls of the developed tools and methods, and suggest future needs. The hypothesis of the study contends that, within the focus of this study, invasion of headwater streams by woody IAPs can result in; · increased channel incision and bank steepening, and · an increase in streambank instability. 1.2 Document Structure Chapters 2 to 4 form a review of current literature to establish a base of understanding of the implications, processes and components involved in the invasion of riparian zones by Invasive Alien Plants. In Chapter 5 the approaches to stream surveying are assessed and selected methods of stream survey seen as applicable to this study are reviewed. Based on these findings, a method of stream survey for application in this study is developed and described in Chapter 6 following a description of the fieldwork sites and methodology. Chapter 7 provides an extensive analysis and exploration of the results of the various components of the fieldwork, which are then discussed in Chapter 8. Chapter 9 outlines final conclusions, analysis of the applicability of the findings, and suggestions with regards to future research needs.
Total evaporation estimation from sugarcane using the scintillation technique.
(2006) Wiles, Luke Wilson.; Blight, Jennifer Joy.; Jewitt, Graham Paul Wyndham.
Ongoing concerns about the efficient and sustainable utilisation of South Africa’s water resources have resulted in much interest regarding the water use of different land uses within a catchment. Research has been focussed on water use by different dryland vegetation, in particular commercial forestry which has been declared a Stream Flow Reduction Activity for which a water use license is required for production. Consequently, concerns about the water use of other dryland crops have lead to a need to quantify water use by other land uses, particularly sugarcane. In this document, previous research focussed on water use by sugarcane is reviewed and summarised, together with an experiment where an energy balance approach has been used to quantify water consumption in the form of total evaporation for an area of sugarcane production in the KwaZulu-Natal Midlands with an assessment of the seasonal variability of this water consumption for a period of 1 year. The study was performed using a Large Aperture Scintillometer to measure sensible heat flux, whilst all other energy balance components, as well as rainfall, soil moisture and other climatic data were obtained using standard methods. Total evaporation was estimated from latent heat flux which was derived as a residual of the energy balance. Total evaporation varies over the year with substantially higher values occurring in summer in response to high energy and water availability. Over the year, the crop used approximately 630mm of water which equates to 53% of rainfall at the site. The two main factors affecting the seasonal variability of water use by sugarcane are net radiation and soil moisture content. In the wetter months when soil moisture is readily available, net radiation limits total evaporation. In the drier months, soil moisture is not as readily available, and limits total evaporation. Air temperature and relative humidity proved to also be important considerations in their effect on total evaporation. The total evaporation estimates obtained could be compared to a baseline (grassland) and used in simulations for a better understanding of the stream flow reduction potential of sugarcane and the seasonal variability thereof.
Tools to assess the ecohydrological impacts of water system innovations
(2009) De Winnaar, Gary.
Water scarce countries such as South Africa are subject to various hydrological constraints, particularly within resource poor farming communities that are reliant on rainfed agriculture. Recent initiatives to address this issue have shifted focus to explore more efficient alternatives to water supply. Adoption of water system innovations through the use of runoff harvesting is one such alternative that provides a means to supplement water use for increased food production. However, increasing the implementation of runoff harvesting, without encountering unintended impacts on downstream hydrological and ecological systems, requires better understanding of the hydrologic and environmental impacts at catchment scale. The objective of this dissertation was to gain knowledge to the ecohydrological impacts that are likely to occur with the adoption of water system innovations as a means for upgrading rainfed smallholder farming systems. To fulfil this objective, a research component was developed whereby tools were utilised to facilitate this process on the basis of two broad aims. The first aim entailed developing a method for locating areas that are most suitable for the adoption of runoff harvesting using Geographical Information Systems (GIS). This was achieved by spatially modelling physical properties of the landscape which influence runoff response. Combining potential runoff with socio-economic factors produced a runoff harvesting map of sites with low, medium and high suitability. This is illustrated by a case study at the Potshini catchment, a small sub-catchment in the Thukela River basin, South Africa. The second aim involved modelling the impacts that runoff harvesting would have on the downstream hydrology and ecology based on the alteration of the flow regimes. To accomplish this, the ACRU Agrohydrological model which was configured to represent runoff harvesting, was used to simulate streamflow for quaternary catchments within the headwaters of the Thukela River basin. Simulated streamflows from ACRU was input into the IHA model to generate ecologically relevant hydrological parameters. Alteration of the flow regime due to runoff harvesting was mostly a reduction in high and low flows however the impacts were insignificant. This suggests that, depending on the intensity of runoff harvesting, downstream ecological impacts are insignificant.
Wetland geomorphology and floodplain dynamics on the hydrologically variable Mfolozi River, KwaZulu-Natal, South Africa.
(2008) Garden, Suzanne.; Ellery, William Nolan.
Wetlands in southern Africa can be considered a rarity, forming despite a regional negative water balance and a continental background of wide scale incision. These particular characteristics lead to southern African wetlands generally forming on drainage lines, where incision has been momentarily paused and water is locally abundant. The exact evolutionary history of valley bottom and floodplain wetlands is varied. However, their development follows four main themes; 1) those that evolve due to resistant lithologies outcropping on a drainage line and acting as local base levels, 2) those that occur on the coast, with current sea level preventing drainage line incision, 3) those that arise from a particular relationship with a trunk or tributary channel that blocks a drainage line with sediment, and finally, 4) those that occur in a region of dramatic loss of confinement, resulting in the formation of a wetland alluvial fan. Despite varied histories, all wetlands share a common thread, developing along a continuum from small and steep unchanneled valley bottom wetlands to large and flat floodplain wetlands. Incision in valley-bottom wetlands is controlled by a geomorphic slope threshold, whereby for a given wetland size, a particular slope may be considered stable. Wetlands exceeding the particular slope for their size are most likely already incised, or are vulnerable to incision in the near future. This thesis examines the general evolution of drainage line wetlands, followed by a detailed study of a large coastal floodplain, the Mfolozi River Floodplain, located on KwaZulu-Natal’s northern coastal plain. The Mfolozi Floodplain is one of South Africa’s largest at 19 000ha and is located just south of the world heritage site of Lake St. Lucia, with the St. Lucia and Mfolozi River mouths occasionally joining at the coast. Although once a mosaic of Cyperus papyrus and Phragmites australis permanent and seasonal wetland, approximately 60% of the floodplain has been reclaimed since the 1920’s for large-scale sugar cane cultivation. A smaller percentage is used for subsistence farming, while the remaining lower portion falls in the Greater St. Lucia Wetlands Park (which was renamed iSimangeliso Park in November 2007). The formation of the large coastal valley in which the Mfolozi Floodplain now sits was created during a period of incision during the last glacial maximum 18 000 BP when sea level was 120m below the current level. The lowered sea level resulted in regional river rejuvenation and valley down cutting. The Mfolozi River valley became deeply incised resulting in the formation of incised meanders upstream of the Lebombo Mountains. Below the mountains, less resistant lithologies of the Maputaland and Zululand Groups allowed the development of a wide coastal valley. Following the last glacial maximum, sea level rose, reaching its present level approximately 6000 BP. As sea level rose, coastal valleys were drowned and began to infill with sediments. Above the floodplain, the Mfolozi River follows a meandering course in an incised confined valley. Upon passing through the Lebombo Mountains, the valley widens considerably from 915 m to over 6 km in just 1.15 km. This rapid change from confinement to a broad floodplain setting results in a reduction of carrying capacity of the Mfolozi River, creating a node of large-scale deposition at the floodplain head in the form of an alluvial fan. Deposition in this region causes a local oversteepening of the valley’s longitudinal profile, with a gradient of 0.1%. Contrastingly, the mid- floodplain is almost flat, with a decrease in elevation of just 1 m over almost 6 km (0.02%). The lower floodplain, where gradient is completely controlled by sea level, has a steeper gradient of 0.05%. The reason for the rather drastic slope break in the mid floodplain is currently unknown, although it may be related to faulting in the underlying Tertiary aged Zululand Group, which is currently concealed by Quaternary deposits. In addition, tributary drainage lines that once flowed into the Mfolozi River have been blocked by long-term sediment accumulation on the floodplain. As a result, these drainage lines have become drowned and provide local conditions for the formation and accumulation of peat. Besides geological setting, hydrology is commonly recognized as being the other most important factor in valley evolution. Flow in the Mfolozi River has been characterized as highly variable relative to the rest of the globe. The Black Mfolozi has the lowest Coefficient of Variation (CV) at 61%, followed by the White Mfolozi at 69% and the Mfolozi River at 79%. In addition, catchment precipitation was shown to be variable, especially when compared to global values. As a result of variable rainfall and discharge, the Mfolozi River shows hysteresis in sediment concentration on an annual scale, and there is an indication that hysteresis may also occur on a longer time scale during wet and dry rainfall cycles. This however, needs to be confirmed with a longerterm data set. Variable discharge and sediment transport leads to different floodplain processes and dynamics than would be expected for a river of regular flow. Since flow is generally very low in the Mfolozi River, and is characterised by a series of extremely large outlier flood events, the persistence of flood features is likely to be large. In addition, it is likely that extreme flood events are the primary drivers of floodplain evolution and dynamics in such variable settings. The Mfolozi Floodplain wetland study throws light on floodplain process rates, and the forces behind floodplain dynamics in such hydrologically variable settings.
A simulation study of cane transport system improvements in the Sezela Mill area.
(2009) Giles, R. C.; Bezuidenhout, Carel Nicolaas.
The South African sugar industry is of significant local and international importance and covers an area in excess of 450 000 hectares. This area yields approximately 21 million tons of sugarcane per annum which is transported almost exclusively by road, from farms to the sugar mills. The industry is under increasing economic pressures to improve its productivity and competitiveness and sugarcane transport in the sugarcane supply chain has been identified as one area where large improvements and associated cost reductions can be made. This is mainly due to the excess in number of vehicles in the inbound transport system, the high relative cost of transport compared to other production costs in producing sugarcane, and the high fixed costs associated with truck fleet operations. A simulation case study of the transport system was completed in 2005 in the Sezela Mill area in which approximately 2.2 million tons of sugarcane is transported per annum over an average distance of 29 km by approximately 120 independently managed vehicles owned by a wide range of hauliers and individual growers. This amounts to an estimated cost of R58 million per annum. This study investigated the potential savings that could occur as a result of a central fleet control system with integrated vehicle scheduling. A scheduling software package named ASICAM, which resulted in significant savings in the timber industry (Weintraub et al, 1996), was applied within the Sezela region. Results suggested that the number of trucks in the fleet could theoretically be reduced by at least 50%, providing that a central office controls vehicle movements and that all hauliers serve all growers in an equitable fashion. In addition, investigations towards decreasing loading times, decreasing offloading times, changing vehicle speeds and increasing payloads by reducing trailer tare mass showed further reductions in the number of trucks required.
Design of a brush cutter blade and its integration into a semi mechanized sugarcane harvesting system.
(2007) Langton, Matthew Innes.
Sugarcane is an important crop for South Africa. It provides employment and valuable foreign
Quantifying and benchmarking irrigation scheme performance with water balances and performance indicators.
(2007) Greaves, Kevin Robert.; Lecler, Neil Louis.; Smithers, Jeffrey Colin.; Ascough, Gregory William.
South Africa is a water scarce country. As pressure on available water resources increases, irrigation, the largest consumer of water, has to find ways of improving water use efficiency. Benchmarking in the irrigation sector has been identified as a suitable technique to implement this improvement. Benchmarking can be broadly defined as the identification and application of organisation specific best practices with the goal of improving competitiveness, performance and efficiency. A South African sugarcane irrigation scheme was identified to investigate a proposed benchmarking methodology. The scheme was unique in that electromagnetic flow meters were utilised and monitored on a daily basis. This facilitated an in depth study into irrigation water use at the scheme. The project focused on three different objectives. The first objective was to determine the losses, and consequently the efficiency, with which the irrigation scheme was able to deliver irrigation water from the water source to the farm boundary during the years 2004 and 2005. This was achieved by completing the water balance for the scheme with specified geographic and temporal boundaries. Results indicated that the scheme was very efficient with a delivery efficiency of 83.4 and 94.0 % for 2004 and 2005 respectively. These efficiencies were above the accepted South African Department of Water Affairs and Forestry (DWAF) standard of 80 %. The temporal distribution of the delivery efficiency was also investigated to identify periods within each year when inefficiencies occurred, and to better understand the nature of potential losses. It was concluded that the investigations into the temporal distributions be utilised together with the water balance approach in future studies into the performance of irrigation water delivery infrastructure at other South African irrigation schemes. The second objective was to calculate a set of internationally applied external irrigation benchmarking indicators. External indicators from the International Water Management Institute (1WMI), the International Program for Training and Research in Irrigation and Drainage (IPTRID) and the Irrigation Training and Research Center (ITRC) were reviewed for application in a South African context. The external indicator analysis highlighted that at a scheme level, insufficient irrigation was occurring to effectively meet the irrigation demand. It was also found that the scheme infrastructure was not the limiting cause of this observation. The external indicator results highlighted the need for additional schemes for comparison purposes. The results from this component of the study also emphasized the importance of stakeholder confidentiality concerns when attempting to implement a benchmarking initiative. The third objective was to rank individual farm performance of all the farms in the scheme, in terms of total farm sugarcane yield and seasonal irrigation water use. Farm yield and irrigated area were obtained to investigate the relationships between yield and irrigation water application. There were substantial variations in total farm yield and water use for both the 2004 and 2005 seasons, indicating much potential for improvement by many farmers relative to each other. The individual seasonal farm water use was also compared to a simulated irrigation demand, as determined with the SAsched irrigation systems and crop yield model. Simulation results with the SAsched model, using representative soils and climate data for the scheme, showed that the majority of farms were under irrigating relative to the simulated demands, especially in the late spring/early summer period. From on-farm irrigation system evaluations that were performed, it was found that irrigation system capacity constraints were not limiting irrigation applications in the majority of farms. Further research in the form of selected soil water monitoring is required to investigate these observations further.
The evaluation of pressure distribution and bulk density models for infield agriculture and forestry traffic.
(2006) Marx, Barend Jan.; Bezuidenhout, Carel Nicolaas.; Lyne, Peter William Liversedge.
There is evidence that soil compaction, through the use of mechanised equipment, causes detrimental effects to soil quality and reduces long-term productivity of soils. For economic reasons, farmers need to purchase larger, heavier machinery in order to cultivate larger areas under crops, resulting in larger forces on the soil. The severity of soil compaction is governed by various soil and vehicle properties and normally causes an increase in the soil's bulk density and a decrease in the air filled porosity. These changes in soil properties have negative effects on crop production and environmental sustainability. The aim of this study was to investigate and develop a model based decision support system for soil compaction management and research. Soil compaction occurs during the transfer of stresses from the tyre interface into the soil. Numerically, it has been modelled using both mechanistic and empirical models, which attempt to simulate the stress propagation and also sometimes the consequent damage to the soil. The SOCOMO soil compaction model is described and this model computes the stress at a point in the soil for any given horizontal and vertical stress distribution at the soil / tyre interface. It has been successfully used in the Netherlands and in Sweden to map the impact on the soil. The SOCOMO model was tested and verified at a forestry site in Richmond, KwaZulu- Natal. Relationships to determine bulk density were also tested and verified. The SOCOMO model performs satisfactory (RMSE = 47.9 kPa), although it tends to overestimate the pressures within the soil. This could be as a result of the high organic carbon content in the particular soil. Models predicting bulk density also performed satisfactory (RMSE = 69.9 kg.m" ), but resultant densities in the soil are generally underestimated. Future research is needed to find better relationships to estimate changes in dry bulk density and to test the model on a wider range of soils. If the model performs satisfactory it could provide a useful tool to determine the impact of soil compaction on crop yield.
An integrated sugarcane supply chain model : development and demonstration.
(2006) Stutterheim, Peter.; Bezuidenhout, Carel Nicolaas.; Lyne, Peter William Liversedge.
The South African sugar industry is a large industry which relies on expensive capital equipment to harvest, transport and process sugarcane. An average of 23 million tons of sugarcane are annually supplied to 14 mills from over 2 000 large-scale commercial growers and 48 000 small-scale growers. Supply chain stakeholders can benefit if operations are successfully streamlined. Computer-based mathematical models have been used in other industries to improve supply chains, especially in forestry, and are expected to play an increasingly important role in future planning and management. Management of sugar supply chains has historically focussed on generating competitive individual supply chain components. However, inter-component optimisation generally disregards many important intra-component interactions. Hence, efficiency improvements may be significantly limited. Integrated supply chain modelling provides a suitable approach for addressing this problem. The aim of this project was to develop and demonstrate, in concept, an integrated supply chain model for the sugar industry. Such a model could be used to address various integrated planning and management problems throughout the supply chain. A review of existing integrated agri-supply chain models was conducted followed by the development of CAPCONN, an integrated sugar supply chain model framework, that incorporate all steps from field to mill back end. CAPCONN estimates sugarcane quality, mill recovery, capacity utilisation and production costs. Bottlenecks are highlighted and the model could contribute towards capacity manipulation for efficiency improvements under different harvesting scenarios. CAPCONN was demonstrated by analysing a number of scenarios in a mechanisation case study at Komati Mill where sugarcane is currently burned and manually cut. A total of twelve scenarios were compared, including variations in cropping system and time of year. The model framework predicted that a decrease in sugarcane quality and sugar recovery would occur under mechanical harvesting scenarios. Estimated production costs were also higher, even though the transport fleet was significantly reduced. A manually cut green (unburned) harvesting scenario showed a further decrease in sugarcane quality and sugar recovery. Mechanical harvesting during wet weather caused a substantial reduction in supply chain capacity and an increase in production costs. CAPCONN output trends compared favourably with measured and observed data, though the magnitude of the trends should be viewed with caution, since the CAPCONN framework is only a prototype. This shows that it may be a suitable diagnostic framework for analysing and investigating the sugarcane supply chain as a single entity. With further development to a model, the CAPCONN model framework could be used as a strategic planning tool although, one drawback is that a relatively large number of technical inputs are required to run the model.
Validation of a vehicle performance modelling system.
(2007) Herbert, Russell Lloyd.; Lyne, Peter William Liversedge.
Transport costs can account for a significant portion of the total production costs in an agricultural system. In order to ensure maximum efficiency of a transport operation, the transport manager is required to select a suitable vehicle and choose the best route. This is a complex process as vehicles should not be selected based solely on lowest capital cost, but with several variables taken into account. In order to determine an optimal haulage system and to aid the decision making process, a computer model called SimTrans has been developed. SimTrans simulates a haulage vehicle travelling on any given route under normal vehicle operating conditions. The model produces a set of simulated vehicle performance results and a summary of trip details. The vehicle input parameters and route details can be modified to enable the user to simulate different vehicle configurations on alternate routes. The SimTrans model was used in this research project as it provides a comprehensive output of simulated results. However, under certain conditions there is variance between actual and the simulated vehicle performance in SimTrans, particularly with the gear selection routines. The primary objective of this research was to refine, calibrate and validate the current SimTrans model. An initial investigation focused on diesel engine management systems for heavy-duty commercial vehicles and how these systems affect a vehicle's performance. This investigation was aimed at gaining an understanding of how performance data could be gathered directly from the onboard vehicle electronics of a haulage vehicle. A data logging system was developed to measure and record certain operating parameters of a haulage vehicle during operation. The system was installed on a Mercedes Benz 2637 and the vehicle was driven on two alternative routes between the Eston Sugar Mill and a loading zone near Mid-Illovo. The Mercedes Benz 2637 used for the vehicle tests was simulated in SimTrans using identical operating conditions of route and speed limits. By comparing the observed and simulated data sets, errors particularly with gear selection routines were identified. The SimTrans model was modified such that these errors were corrected and a new gear skipping routine was added. The modified SimTrans model was validated through a comparison of a new set of simulated results with the observed data. The modified model showed significant improvement in simulation accuracy over the previous version of SimTrans.
Development of a climatic soybean rust model and forecasting framework.
(2009) Van Niekerk, Lauren Michelle.
Soybean rust (SBR), caused by the fungus Phakopsora pachyrhizi Syd., is a real threat to soybean crops in South Africa. Its ability to spread rapidly and its potential to severely reduce yields have earned it the reputation as the most destructive foliar disease of soybeans. SBR has been reported in South Africa every year since its arrival in 2001. While extensive research had been done on the epidemiology and fungicide application requirements in South Africa, no work into the long term climatic vulnerability of soybean production areas to SBR had been done. This meant soybean producers do not know whether SBR is a threat in their areas. Through this research a SBR algorithm was developed using readily available climate data, viz. temperature and rainfall, to create a daily index specifying the climatic vulnerability of SBR infection. The algorithm was applied to a 50 year historical climate database, and a series of maps was created illustrating the long term vulnerability of different areas to SBR infection. These maps allow soybean producers to understand the climatic vulnerability of their area to SBR infection. Time series graphs were created for selected key soybean production areas to allow soybean producers to distinguish periods of high and low climatic risk during the season. This may help with decisions regarding the planting times, the maturation rate of different cultivars as well as the timing and application of fungicides. The framework for a near real time forecasting system was created outlining how the system could amalgamate recently recorded and forecasted weather data, run it through the SBR algorithm and provide a near real time, as well as forecasted vulnerability, based on the climatic conductivity for SBR infection. Anticipated limitations and difficulties on developing the forecasting system are also outlined.
Agroclimatic response mapping for sugarcane production in southern Africa.
(2008) Hull, Phillip John.; Schulze, Roland Edgar.
As is the case in many other regions in the world, sugarcane production in southern Africa is affected by a wide range of climatic conditions, which can vary considerably from location to location and from year to year. As a result, the season length and growth cycles of sugarcane in southern Africa differ greatly. Such conditions include the hot and dry regions of northern KwaZulu-Natal, Swaziland and Mpumalanga, where sugarcane is mostly irrigated, to the humid sub-tropical coastal belt extending from the far north coast of KwaZulu-Natal to areas in the Eastern Cape, as well as the cool frost prone midlands regions of KwaZulu-Natal. Owing to the wide range of climatic conditions in which sugarcane is grown in southern Africa, there are many different external factors that affect sugarcane production, including a range of pests and diseases, frost occurrences and variations in soil water. The objective of this research was to (1) identify a number of important variables that affect cane production in southern Africa, (2) employ suitable models to reflect these variables, and (3) simulate and map the extent and severity of these variables at a high spatial resolution over southern Africa. Such variables include the Eldana saccharina and Chilo sacchariphagus stalk borers, sugarcane rust fungus, heat units with selected base temperatures, frost, soil water content, soil compaction, irrigation water demand, conducive and non-conducive growing conditions, flowering proficiencies for sugarcane, sugarcane yields and yield increments per unit of irrigation. The distribution patterns of the above-mentioned variables relied greatly upon the various models employed to represent them, as well as the accuracy of the temperature and rainfall databases to which the various models were applied. Although not definitive, the models used to reflect the variables which had been identified were considered to be generally satisfactory. The resolution at which the variables which had been identified in this study were mapped, was also found to be adequate.
Improved estimation of catchment rainfall for continuous simulation modelling.
(2005) Frezghi, Mehari Suim.; Smithers, Jeffrey Colin.
Long sequences of rainfall at fme spatial and temporal details are increasingly required, not only for hydrological studies, but also to provide inputs for models of crop growth, land fills, tailing dams, disposal of liquid waste on land and other environmentally-sensitive projects. However, rainfall records from raingauges frequently fail to meet the requirements of the above studies. Therefore, it is important to improve the estimation of the depth and spatial distribution of rainfall falling over a catchment. A number of techniques have been developed to improve the estimation of the spatial distribution of rainfall from sparsely distributed raingauges. These techniques range from simple interpolation techniques developed to estimate areal rainfall from point rainfall measurements, to statistical and deterministic models, which generate rainfall values and downscale the rainfall values based on the physical properties of the clouds or rain cells. Furthermore, these techniques include different statistical methods, which combine the rainfall information gathered from radar, raingauges and satellites. Although merging the radar and raingauge rainfall fields gives a best estimate of the "true rainfall field", the length of the radar record and spatial coverage of the radar in a country such as South Africa is relatively short and hence is of limited use in hydrological studies. Therefore, the relationship between the average merged rainfall value for a catchment and a "driver" station, which is selected to represent rainfall in the catchment, is developed and assessed in this study. Rainfall data from the Liebenbergsvlei Catchment near Bethlehem in the Free State Province and a six-month record of radar data are used to develop relationships between the average merged subcatchment rainfall for each of the Liebenbergsvlei subcatchments and a representative raingauge selected to represent the rainfall in each of the subcatchments. The relationships between daily raingauges and the average rainfall depth of the subcatchments are generally good and in most of the subcatchments the correlation coefficient is greater than 0.5. It was also noted that, in most of the subcatchments, the daily raingauges overestimate the average areal rainfall depth of the subcatchments. In addition, the String of Beads Model (SBM) developed by Clothier and Pegram (2002) was used to generate synthetic rainfall series for the Liebenbergsvlei catchments. The SBM is able to produce rainfall values at a spatial resolution of IxI km with a 5 minute temporal resolution. The SBM is a high-resolution space-time model of radar rainfall images, which takes advantage of the detailed spatial and temporal information captured by weather radar and combines it with the long-term seasonal variation captured by a network of daily raingauges. Statistics from a 50 year period of generated rainfall values were compared with the statistics computed from a 50 year raingauge data series, and it was found that the generated rainfall values mimic the rainfall data from the raingauges reasonably well. The relationship developed between the merged catchment rainfall values and driver rainfall station values, which are selected to represent the mean areal rainfall of the subcatchment, was used to adjust the Conventional Driver rainfall Station (CDS) into Modified Driver Station (MDS) values. Streamflow was simulated using both the CDS and MDS rainfall compared against the observed streamflow from the Liebenbergsvlei catchment. In general, the streamflow simulated by the ACRU model do not correlate well with the observed streamflow, which is attributed to unrealistic observed flow and inter-catchments transfers of water. However, it is noted that the volume of streamflow simulated with the MDS rainfall is only 71 % of that simulated with the CDS rainfall, thus highlighting the limitation of using the CDS rainfall approach for modelling and the need to apply the methodology to improve the estimation of catchment rainfall developed in this study to other catchments in South Africa.
The design and testing of soil pressure sensors for in-field agricultural and forestry traffic.
(2005) Eweg, Jonathan Lindsay.; Lyne, Peter William Liversedge.; Bezuidenhout, Carel Nicolaas.
River stage or flow rates are required for the design and evaluation of hydraulic structures. Most river reaches are ungauged and a methodology is needed to estimate the stages, or rates of flow, at specific locations in streams where no measurements are available. Flood routing techniques are utilised to estimate the stages, or rates of flow, in order to predict flood wave propagation along river reaches. Models can be developed for gauged catchments and their parameters related to physical characteristics such as slope, reach width, reach length so that the approach can be applied to ungauged catchments in the region. The objective of this study is to assess Muskingum-based methods for flow routing ill ungauged river reaches, both with and without lateral inflows. Using observed data, the model parameters were calibrated to assess performance of the Muskingum flood routing procedures and the Muskingum-Cunge method was then assessed using catchment derived parameters for use in ungauged river reaches. The Muskingum parameters were derived from empirically estimated variables and variables estimated from assumed river cross-sections within the selected river reaches used. Three sub-catchments in the Thukela catchment in KwaZulu-Natal, South Africa were selected for analyses, with river lengths of 4, 21 and 54 km. The slopes of the river reaches and reach lengths were derived from a digital elevation model. Manning roughness coefficients were estimated from field observations. Flow variables such as velocity, hydraulic radius, wetted perimeters, flow depth and top flow width were determined from empirical equations and cross-sections of the selected rivers. Lateral inflows to long river reaches were estimated from the Saint-Venant equation. Observed events were extracted for each sub-catchment to assess the Muskingum-Cunge parameter estimation method and Three-parameter Muskingum method. The extracted events were further analysed using empirically estimated flow variables. The performances of the methods were evaluated by comparing both graphically and statistically the simulated and observed hydrographs. Sensitivity analyses were undertaken using three selected events and a 50% variation in selected input variables was used to identify sensitive variablesThe performance of the calibrated Muskingum-Cunge flood routing method using observed hydrographs displayed acceptable results. Therefore, the Muskingum-Cunge flood routing method was applied in ungauged catchments, with variables estimated empirically. The results obtained shows that the computed outflow hydrographs generated using the Muskingum-Cunge method, with the empirically estimated variables and variables estimated from cross-sections of the selected rivers resulted in reasonably accurate computed outflow hydrographs with respect to peak discharge, timing of peak flow and volume. From this study, it is concluded that the Muskingum-Cunge method can be applied to route floods in ungauged catchments in the Thukela catchment and it is postulated that the method can be used to route floods in other ungauged rivers in South Africa.
A study on reducing primary transport costs in the South African timber industry.
(2005) Lusso, Cary D.; Lyne, Peter William Liversedge.; Bezuidenhout, Carel Nicolaas.
Harvesting and transport accounts for up to 70% of the total production cost of roundwood in South Africa. This invokes an interest to improve harvesting systems through the introduction of improved equipment, road networks and more refined operating techniques. A literature review was conducted which investigated the various harvesting systems and equipment with a focus on ground based extraction, as it accounts for 96% of the timber being extracted annually in South Africa. A review of forest roads in South Africa was also conducted and it was concluded that at present there has been little focus on the upgrading and maintenance of forest road networks. It was concluded that the most significant reduction in transport costs would be achieved by reducing the distances travelled by expensive extended pnmary transport (R5.83 t-1.km-1) and by allowing less expensive secondary terminal transport (R0.4 t-1.km-1) to move further into the plantations. This could only be achieved by investing large amounts of capital into the upgrading of forest roads to a standard suitable to service secondary transport vehicles. A model was developed which was able to determine the tonnage of timber needed to flow over a particular road that will warrant the upgrading cost. The model was applied to two study areas, the first study yielded no results due to the already dense network of B- class roads, possibly excessive. The second study area identified three possible road upgrades to improve the existing transport system. A full costing of the existing and modified transport system was completed and a significant cost saving was shown, not accounting for the road upgrading cost. Capital budgets were used to account for more complex parameters, such as tax and discount rates, previously excluded from the simple model. These were used to determine the economic viability of the upgrades and to evaluate the suitability of the model. The model proved to be successful and confirmed that forest roads can be optimised accompanied by significant cost savings. The model is generic and simple allowing for easy application to a variety of situations and is also flexible to modifications.

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