Environmental Hydrology

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Hillslope experiments in the north east Cape region to measure and model subsurface flow processes.
(1997) Esprey, Luke John.; Lorentz, Simon Antony.
Several hydrological studies claim that available water resources in a catchment are affected by large scale afforestation, especially where the regional rainfall is considered marginal for the support of silviculture. Nevertheless, the mechanisms and magnitude of the perturbations to the receiving water resources due to afforestation are still not clearly understood. To improve this understanding an intensive hydrological experiment has been initiated in the small grassed Weatherly catchment of the Mondi, North East Cape Forests. Details of the soil water dynamics on the Molteno formations in the catchment have been be studied. This research presents a description and first results of the establishment of an experiment which comprises monitoring the water budget of the grassed catchment prior to the afforestation of the catchment to plantations of exotic trees. The studies currently include, monitoring the infiltration and redistribution of soil water on a hillslope as well as monitoring of interflow mechanisms and localised mechanisms of soil water accumulation influenced by the topography and geology of the catchment. In addition to the intensive soil water monitoring, specific experimentation has been conducted at various locations on the hillslope. These comprise macropore flow process studies and 2-dimensional tracer experiments. Details of these experiments as well as the automated soil water and groundwater monitoring instrumentation are presented. An intensive soil survey on a 30 m x 30 m grid as well as a comprehensive measurement strategy of soil physical and hydraulic properties are highlighted. A review of 2-dimensional numerical hillslope soil water process models is also presented. Results from this research show that on hillslopes underlain by Molteno sandstones localised perched water tables form. These water bodies, upon reaching a critical height above the bedrock cascade downslope as interflow recharging the water bodies downslope. The response to infiltration increases downslope and in the toe region interflow occurs readily in response to rainfall compared to the midslope where substantial rain needs to infiltrate.
An analysis of baseflow recession in the Republic of South Africa.
(1997) Hughes, Gregory Owen.; Schulze, Roland Edgar.
Demands on the water resources of South Africa are ever increasing owing to population growth and increased development of urban, peri-urban and rural communities. Problems in terms of water quantity and quality are likely to be experienced during baseflow recessions. It is therefore imperative that water resources managers not only understand these baseflow periods of streamflow, but are able to model them with confidence. Research for this study thus included a comprehensive literature survey of the factors which affect baseflow as well as the approaches that previous studies have utilised to analyse and model baseflow recession. The primary aims of this study were to establish a streamflow database, to construct master recession curves (MRCs) for each catchment under consideration, evaluate the assumption that South African rivers recede exponentially, to determine a representative set of catchment characteristics for use in the baseflow recession analysis, to attempt to explain the MRC trends using these catchment characteristics and to investigate the feasibility of establishing a rule based model for baseflow recession. A streamflow database for South Africa was therefore established. This consisted initially of 202 catchments which were deemed to be recording natural streamflow. MRCs were established for 134 of these catchments. Those MRCs which were established indicate that the majority of South African rivers do not conform to an exponential model of recession. In order to account for the trends defined by the MRCs, catchment area, average catchment slope, drainage density, mean annual precipitation, rainfall concentration, rainfall seasonality, two independent estimates of groundwater recharge and a geological index were calculated for each catchment. Limited success was achieved when the data set was divided into subsets in order to group catchments with similar baseflow recession responses. The geological composition of the catchments appeared to provide the best results in that those trends exhibited by the MRCs could be explained by the types and proportions of the lithologies present. Owing to the lack of readily useable results it was concluded that until further results were forthcoming the development of a rule based model for baseflow recession analysis in South Africa would be premature. The establishment of a readily accessible database containing streamflows and associated catchment characteristics lends itself to future research.
Development and evaluation of techniques for estimating short duration design rainfall in South Africa.
(1998) Smithers, Jeffrey Colin.; Schulze, Roland Edgar.; Pegram, Geoffrey Guy Sinclair.
The objective of the study was to update and improve the reliability and accuracy of short duration (s 24 h) design rainfall values for South Africa. These were to be based on digitised rainfall data whereas previous studies conducted on a national scale in South Africa were based on data that were manually extracted from autographic charts. With the longer rainfall records currently available compared to the studies conducted in the early 1980s, it was expected that by utilising the longer, digitised rainfall data in conjunction with regional approaches, which have not previously been applied in South Africa, that more reliable short duration design rainfall values could Ix: estimated. A short duration rainfall database was established for South Africa with the majority of the data contributed by the South African Weather Bureau (SAWB). Numerous errors such as negative and zero time steps were identified in the SAWB digitised rainfall data. Automated procedures were developed to identify the probable cause of the errors and appropriate adjustments to the data were made. In cases where the cause of the error could be established, the data were adjusted to introduce randomly either the minimum, average or maximum intensity into the data as a result of the adjustment. The effect of the adjustments was found to have no significant effect on the extracted Annual Maximum Series (AMS). However, the effect of excluding erroneous points or events with erroneous points resulted in significantly different AMS. The low reliability of much of the digitised SAW B rainfall data was evident by numerous and large differences between daily rainfall totals recorded by standard, non-recording raingauges, measured at 08:00 every day, and the total rainfall depth for the equivalent period extracted from the digitised data. Hence alternative techniques of estimating short duration rainfall values were developed, with the focus on regional approaches and techniques that could be derived from daily rainfall totals measured by standard raingauges. Three approaches to estimating design storms from the unreliable short duration rainfall database were developed and evaluated. The first approach used a regional frequency analysis, the second investigated scaling relationships of the moments of the extreme events and the third approach used a stochastic intra-daily model to generate synthetic rainfall series. In the regional frequency analyses, 15 relatively homogeneous rainfall clusters were identified in South Africa and a regional index storm based approach using L-moments was applied. Homogeneous clusters were identified using site characteristics and tested using at-site data. The mean of the AMS was used as the index value and in 13 of the 15 relatively homogeneous clusters the index value for 24 h durations were well estimated as a function of site characteristics only, thus enabling the estimation of 24 h duration design rainfall values at any location in South Africa. In 13 of the 15 clusters the scaling properties of the moments of the AMS were used to successfully estimate design rainfall values for duration < 24h, using the moments of the AMS extracted from the data recorded by standard raingauges and regional relationships based on site characteristics. It was found that L-moments scaled better and over a wider range of durations than ordinary product moments. A methodology was developed for the derivation of the parameters for two Bartlett-Lewis rectangular pulse models using only standard raingauge data, thus enabling the estimation of design values for durations as short as 1 h at sites where only daily rainfall data are available. In view of the low reliability of the majority of short duration rainfall data in South Africa, it is recommended that the regional index value approach be adopted for South Africa, but scaled using values derived from the daily rainfall data. The use of the intra-daily stochastic rainfall models to estimate design rainfall values is recommended as further independent confirmation of the reliability of the design values.
Simulation modelling of sugarcane harvest-to-crush delays.
(1998) Barnes, Andrew.; Meyer, E.; Hansen, Alan Christopher.; Lyne, Peter William Liversedge.
Long delays between harvesting and crushing of sugarcane lead to excessive deterioration in the quality of sugarcane. The aim of this project was to develop a computer based model of sugarcane harvesting and delivery systems that could be used to investigate methods of reducing harvest-to crush delays. A literature review was conducted and simulation modelling was chosen as the most appropriate modelling technique for the situation of sugarcane harvesting and delivery and the purposes of this project. The Arena modelling system was chosen as the simulation software with which to construct the model. A model was developed on the scale of a particular sugar mill and the area of farms supplying it with cane. The Sezela mill on the south coast of KwaZulu-Natal, South Africa was chosen as a case study on which to develop and test the model. The model integrated a harvesting and transport section which represented all the individual farms or combinations of farms in the area with a millyard section. After the model had been verified and validated, it was used to investigate the effect of a number of different scenarios of harvesting and delivery systems and schedules on harvest-to-crush delays in the Sezela mill area. The results of the experimental runs performed with the model indicated that the most significant decreases in harvest-to-crush delays could be brought about by matching harvesting, delivery and milling cycles as closely as possible. It was also evident that burn-to-cut delays where daily burning is not practised constitute a large proportion of overall harvest-to crush delays. The model proved to be useful in making comparisons between systems and in providing a holistic view of the problem of harvest-to-crush delays. Recommendations for future developments of the model include adding a mechanical harvesting component and making the model more easily applicable to other mill areas.
Development and evaluation of a sugarcane yield forecasting system.
(2000) Lumsden, Trevor Graeme.; Schulze, Roland Edgar.
There is a need in the South African sugar industry to investigate improved techniques for forecasting seasonal sugarcane yields. An accurate and timely forecast of seasonal cane yield is of great value to the industry, and could potentially allow for substantial economic savings to be made. Advances by climatologists have resulted in increasingly accurate and timely seasonal climate forecasts. These advances, coupled with the ongoing advances made in the field of crop yield simulation modelling, present the sugar industry with the possibility of obtaining improved cane yield forecasts. In particular, the lead time of these forecasts would be improved relative to traditional techniques. Other factors, such as the flexibility offered by simulation modelling in the representation of a variety of seasonal scenarios, would also contribute to the possibility of obtaining improved cane yield forecasts. The potential of applying crop yield simulation models and seasonal rainfall forecasts in cane yield forecasting was assessed in this research project. The project was conducted in the form of a case study in the Eston Mill Supply Area. Two daily time step cane yield simulation models, namely the ACRU-Thompson and CANEGRO-DSSAT models, were initially evaluated to test their ability to accurately simulate historical yields given an observed rainfall record. The model found to be the more appropriate for yield forecasting at Eston, the ACRU-Thompson model, was then used to generate yield forecasts for a number of seasons, through the application of seasonal rainfall forecasts in the model. These rainfall forecasts had previously been translated into daily rainfall values for input into the model. The sugarcane yield forecasts were then evaluated against observed yields, as well as against forecasts generated by more traditional methods, these methods being represented by a simple rainfall model and Mill Group Board estimates. Although the seasonal rainfall forecasts used in yield forecasting were found not to be particularly accurate, the proposed method provided more reliable cane yield forecasts, on average, than those using the traditional forecasting methods. A simple cost-benefit analysis indicated that the proposed method could potentially give rise to the greatest net economic benefits compared to the other methods. Recommendations are made for the practical implementation of such a method. Future areas of research are also identified.
A high resolution digital system for automated aerial surveying.
(2000) Coleman, Andrew Stuart.; Hansen, Alan Christopher.
Resource managers frequently require moderate to high resolution imagery within short turnaround periods for use in a GIS-based management system. These spatial data can greatly enhance their ability to make timely, cost-saving decisions and recommendations. MBB Consulting Engineers, Inc., of Pietermaritzburg, South Africa had for many years made use of airborne videography to provide the imagery for several resource-based applications. Applications included detailed land use mapping in various South African river catchments and identification, density classification and mapping of alien vegetation. While the system was low cost and easy to operate, MBB had found that their system was inherently limited, particularly by its lack of automation and poor spatial resolution. This project was started because of a need to address these limitations and provide an airborne remote sensing system that was more automated and could produce higher resolution imagery than the existing system. In addition, the overall cost and time required to produce a map of the resource of interest needed to be reduced. The system developed in this project aimed to improve upon the pre-flight planning and in-flight image acquisition aspects of the existing system. No new post-flight image processing procedures were developed, but possible future refinement of the post-flight image processing routine was considered throughout the development of the system. A pre-flight planning software package was developed that could quickly and efficiently calculate the positions offlight lines and photographs or images with a minimum of user input. The in-flight image acquisition setup developed involved the integration of a high resolution digital still camera, a Global Positioning System (GPS), and camera control software. The use of the rapidly developing and improving technology of a digital still camera was considered to be a better alternative than a video graphic or traditional film camera system for a number of reasons. In particular, digital still cameras produce digital imagery without the need for development and scanning of aerial photographs or frame grabbing of video images. Furthermore, the resolution of current digital still cameras is already significantly better than that of video cameras and is rivalling the resolution of 35rnm film. The system developed was tested by capturing imagery of an urban test area. The images obtained were then rectified using photogrammetric techniques. Results obtained were promising with planimetric accuracies of 5 to 1 Om being obtained. From this test it was concluded that for high accuracy applications involving numerous images, use would be made of softcopy photogrammetric software to semi-automatically position and rectify images, while for applications requiring fewer images and lower accuracy, images could be rectified using the simpler technique of assigning GCPs for each image from scanned orthophotos.
Defining small catchment runoff responses using hillslope hydrological process observations.
(2000) Hickson, Rory Macready.; Lorentz, Simon Antony.
The Umzimvubu catchment on the eastern coastal escarpment of South Africa is sensitive to anthropogenic influences,with commercial and subsistence agriculture, irrigation, domestic and rural settlements and forestry compete for water use. An adequate supply of water to the region is seen as imperative in the light of the recent establishment of forest cultivation. In order to provide a sound assessment of the impacts of afforestation on the catchment, the subsurface hydrological processes of hillslopes on the Molteno sedimentary formations of the region must be clearly understood. Since the runoff hydrograph is, to a large degree, dependent on the subsurface processes, a number of models that simulate small catchment runoff have been developed. However, recent successful application of tracer techniques to hydrological modelling has shown that the subsurface processes are still not fully understood (Schultz, 1999), and whether or not the subsurface processes are modelled adequately is most often not verified, since there is a lack of relevant data. It is, therefore imperative that the subsurface component of these small catchment runoff models be improved. This can be achieved by first observing detailed subsurface water dynamics and assessing these against the catchment runoff response. In this dissertation, results from a detailed experiment that was initiated in a 1.5 km2 catchment in the northern East Cape Province are shown. Nests of automated tensiometers, groundwater level recorders and weather stations have been placed at critical points around the catchment, and these , together with soil hydraulic and physical characteristics are used to define and identify the dominant hillslope processes. Two crump weirs record runoff from these hillslopes. The results of this subsurface study highlight the dynamics of surface and subsurface water in the hillslope transects. It is evident that the subsurface processes are strongly influenced by the -bedrock topography as well as the soil characteristics, such as macropore flow and deep percolation. Using the monitored data and 2-D vadose zone modelling, the dominant hillslope processes have been defined and are used to aid in the selection of critical parameters to be used in estimating the catchment runoff. Results show that a clear understanding of the subsurface dynamics can lead to a realistic estimation of catchment scale runoff response.
Procedures for estimating gross irrigation water requirement from crop water requirement.
(2001) Ascough, Gregory William.; Kiker, Gregory Alan.
The goal of irrigation is to supply sufficient water for crop growth to all areas within a field. Therefore, the uniformity of application of irrigation water is of great importance. The objectives of this study were to quantify the performance of irrigation systems under field conditions using standard evaluation techniques and to investigate the use of spatial statistics to characterise the spatial variability of application. The main objective was to develop techniques to estimate gross irrigation water requirement that incorporates the uniformity of application. Different practitioners have given different definitions to the criteria used to evaluate the performance of an irrigation system. A literature review was conducted to determine the current definitions used and the factors that affect these performance criteria. The theory and application of spatial statistics was investigated in order to charaterise spatial distribution of irrigation water. The spatial distribution of irrigation water under centre pivots was determined using field measurements. A number of centre pivot, sprinkler, floppy, drip and micro-irrigation systems were evaluated using standard techniques. The results from the evaluation of spatial data show that this approach is useful to determine a map of the distribution of applied irrigation water. Due to the smoothing characteristic of the spatial statistical method employed, the maps have a uniformity that is greater than in reality. The results from the standard evaluation techniques show that quick and representative results for the performance of an irrigation system can be obtained. The distribution uniformity has an affect on the efficiency of a system and should therefore be included in the calculation of the gross irrigation water requirement. The methods for these calculations are discussed. Further research needs to be conducted to determine actual distribution uniformities and application efficiencies for irrigation systems under various field conditions. This will provide useful standards to include in the calculation of gross irrigation water requirements.
A methodology for assessing irrigation practice in small scale community gardening.
(2001) Sihlophe, Nhlanhla.; Lorentz, Simon Antony.
The challenges facing small scale irrigation development in South Africa are varied and complex. This complexity is exacerbated by the many years of systematic neglect, in tandem with material and intellectual impoverishment of the majority of participants in this agricultural sector. Attempting to juggle sustainable development of small scale agriculture and environmental and socio-economic advancement is difficult, but there is sufficient evidence in the literature to suggest that small scale agriculture is increasing not only in South Africa but in Sub-Saharan Africa (Collier and Field, 1998) There is no doubt that this observed increase in irrigated communal gardens result from their increasingly important role of providing food security and as means of augmenting family income. Hence the government,NGO' s and other private sector organisations have increased their support for these small scale agricultural initiatives. Small scale agriculture is therefore increasingly becoming a common land use, and with this increased support, it is likely to become a major water user, particularly as it is located in close proximity to the water source. Hence both practices and processes for small scale agriculture require careful study. Irrigation practices have been studied in KwaZulu-Natal where small scale community gardens are continuously developing. The study included two locations near Pietermaritzburg. The first, at Willowfontein, involved irrigation by furrow , and the second, at Taylors Halt, involved irrigation by hand, using containers. The dynamics of the subsurface flow was monitored using tensiometry and modelled in detail using a two dimensional, soil physics model, Hydrus-2D, to evaluate the application efficiency. This study consisted of three parts viz: socio-economic system appraisal, technical measurement and monitoring, and modelling. Important findings obtained include the following: The highlighting of pertinent socio-economic issues governing water use and allocation and other operations in developing small scale agricultural conditions, including constraints to the development of this sector under the conditions described. The demonstration of the use of reasonably inexpensive, but sophisticated measuring techniques to observe the soil water processes in small scale community gardening practices. Accurate simulations of soil water infiltration,redistribution and uptake using the Hydrus2D model. With these successful simulations, together with the results of the social system appraisal, more efficient irrigation scenarios are proposed and evaluated. The development of a methodology that could be used to assess small scale irrigation efficiencies, with computer simulation models used as tools to conduct such an assessment.
Refinement of modelling tools to assess potential agrohydrological impacts of climate change in southern Africa.
(2001) Perks, Lucille Annalise.; Schulze, Roland Edgar.
Changes in climate due to anthropogenic influences are expected to affect both hydrological and agricultural systems in southern Africa. Studies on the potential impacts of climate change on agrohydrological systems had been performed previously in the School of Bioresources Engineering and Environmental Hydrology (School of BEEH). However, refinement of these modelling tools and restructuring of the databases used was needed to enable more realistic and dynamic simulations of the impacts of changes in climate. Furthermore, it was realised that modifications and linkages of various routines would result in a faster processing time to perform climate impact assessments at the catchment scale. Baseline ("present") climatic information for this study was obtained from the School of BEEH's database. Scenarios of future climate were obtained from six General Circulation Models (GCMs). Output from the five GCMs which provided monthly climate output was used in the climate impact assessments carried out. Potential changes in variability of rainfall resulting from climate change was assessed using the daily climate output from the sixth GCM. As the spatial resolution of the climatic output from these GCMs was too coarse for use in climate impact studies the GCM output was interpolated to a finer spatial resolution. To assess the potential impact of climate change on water resources in southern Africa the ACRU hydrological modelling system was selected. The ACRU model was, however, initially modified and updated to enable more dynamic simulation of climate change. In previous hydrological studies of climate change in southern Africa Quaternary Catchments were modelled as individual, isolated catchments. To determine the potential impact of changes in climate on accumulated flows in large catchments the configuration of the Quaternary Catchments needed to be determined and this configuration used in ACRU. The changes in hydrological responses were calculated both as absolute differences between future and present values and the ratio offuture hydrological response to the present response. The large degree of uncertainty between the GCMs was reflected in the wide range of results obtained for the water resources component of this study. In addition to the climate impact studies, sensitivity and threshold studies were performed using ACRU to assess the vulnerability of regions to changes in climate. Potential change in the yields and distributions of parameters important to agriculture, such as heat units, crops, pastures and commercial tree species were assessed using simple crop models at a quarter ofdegree latitude / longitude scale. Most species were simulated to show decreases in yields and climatically suitable areas. There are many sources of uncertainties when performing climate impact assessments and the origins of these uncertainties were investigated. Lastly, potential adaptation strategies for southern Africa considering the results obtained are presented.
Hydrological modelling applications for water resources management in the Mkomazi Catchment.
(2001) Taylor, Valerie.; Schulze, Roland Edgar.
Predictions that water shortages will constrain economic growth in South Africa by 2025 have led to increased concerns among water resource managers that there is a need for comprehensive water management strategies. To this extent the new South African Water Act requires that water resource allocation be approached in a more equitable and conservative way than in the past in order to sustain water resources for catchment development. This includes protection of the water resource base by the setting aside of a health Reserve for basic human needs and for the ecological functioning of rivers. At a time when water resource management is shifting from the practice of large dam construction to reconciling water demand with water supply in more holistic strategies, the Mkomazi Catchment in KwaZulu-Natal provides an opportunity to investigate some of the major issues that dominate contemporary water resource management. Presently (2001), there are no impoundments on the Mkomazi River and the catchment is generally underdeveloped. These factors have provided the impetus for the Department of Water Affairs and Forestry's proposed inter-basin transfer scheme to use the surplus flow in the Mkomazi Catchment to augment the water resources of the neighbouring Mgeni system. Impact-of-Iand-use and development scenario studies, using the ACRU agrohydrological modelling system, were performed to simulate the impacts of (a) baseline land cover, (b) present land use, (c) the first phase of the Mkomazi-Mgeni Transfer Scheme and (d) potential climate change on the hydrological dynamics of the Mkomazi Catchment. The results indicate that the change from baseline land cover conditions to present land use conditions has little impact on the annual water resources of the Mkomazi River. This is especially so in the upper catchment where there is little anthropogenic development and from where the planned inter-basin transfer will be made from the proposed Smithfield Dam. Although the impacts of commercial forestry and irrigation in the middle and lower catchment impose local stress on streamflow generation, they do not detract substantially from the main downstream flows. Evaluation of the impacts of the proposed Smithfield Dam on annual streamflow generation revealed that there is more than sufficient water in the upper Mkomazi Catchment to sustain the inter-basin transfer under present climatic conditions. However, under potential climate change the median annual Mkomazi streamflows at the estuary could be reduced by 46% if the dam was constructed, compared with a 22% reduction under present climatic conditions. The impacts of catchment development on the seasonal low flows within the Mkomazi Catchment indicated that those areas which are already heavily utilised by afforestation and, particularly, by irrigated land use are unlikely to be able to support any further large scale commercial agricultural development, even under present climatic conditions. Water management strategies for the Mgeni system will impact on potential water allocation within the Mkomazi Catchment. The results of the impacts studies were used to assess the water demand of the major water-use sectors and the availability of streamflows for further allocation was assessed. Present total annual water demands of Mkomazi streamflows is minimal. Even allowing for the environmental demand in the Mkomazi Catchment, as identified by the Building Block Methodology during an instream flow requirements workshop, as well as the first phase of the inter-basin transfer, there would be surpluses of 66%, 43%, 42% and 45% of streamflows, respectively, at the four instream flow requirement sites on the Mkomazi River. The results of the Mkomazi instream flow requirements workshop were revisited to assess the achievability of the recommended flows within the ACRU generated daily time series of streamflows for each of the scenarios simulated, at the each of the four instream flow requirement sites on the Mkomazi River. The results confirmed the need to ascertain the Mkomazi River's natural flow variability, and to assess how much alteration is likely under development of the Mkomazi Catchment. The Indicators of Hydrologic Alteration and Range of Variability Approach methodologies were used to determine which components of the streamflow regime would be most impacted by the inter-basin transfer. Hypothetical, yet realistic, upper and lower management target thresholds were applied to determine the range of variation experienced by the streamflow regime of the Mkomazi, under both pre- and post-dam construction conditions, and to evaluate a preliminary assessment of the characteristics of the streamflow regime required to meet environmental sustainability. The issues raised by potentially conflicting water uses within catchments in South Africa have indicated that any approach to address the increasing complexity of water resource problems, and the management thereof, requires effective hydrological modelling.
An evaluation of selected appropriate irrigation technologies for small-scale farmers.
(2001) Kedge, Caryn Julie.; Kiker, Gregory Alan.
South Africa lacks affordable irrigation technologies suited entirely to the needs of small-scale farmers. This is mainly due to the past emphasis on large, commercial farming technologies and the misunderstanding that emerging farmers can utilise scaled down versions of such technologies. It is now believed that increased irrigation amongst smallholders could largely assist with food security and poverty alleviation in South Africa. The object of this project was therefore to evaluate selected appropriate irrigation technologies that are currently being used in other developing countries with the intention of introducing them into South Africa. A literature review on all the irrigation technologies currently being used by small-scale farmers in South Africa was performed. The literature review provided information on the factors affecting the adoption of irrigation technologies. Selected technologies, namely, various low-cost, manual pumps and drip irrigation kits were then imported and evaluated under local conditions. The evaluation process was divided into two sections. Qualitative evaluations were carried out on farms and by farmers themselves and quantitative evaluations were carried out in laboratories and closely monitored field trials. A South African prototype pump was then designed and built following the knowledge gained from testing the imported pumps. The prototype was tested and then refined and rebuilt. The qualitative test results showed a very positive reaction from farmers towards the pumps. The drip irrigation kits were often not used as a result of a lack of understanding by the farmers. The laboratory test phase highlighted the more critical components of the pumps. A recommended introduction strategy was then developed and is presented. This evaluation process and introduction strategy could in future be used as a guideline when developing other suitable technologies for small-scale farmers.I wish to certify that the work reported in this dissertation is my own unaided work except where specific acknowledge is made. In addition I wish to declare that this dissertation has not been submitted for a degree in any other university.
The development and evaluation of an operating rule framework for the ACRU agrohydrological modelling system.
(2001) Butler, Andrew John Edward.; Smithers, Jeffrey Colin.; Jewitt, Graham Paul Wyndham.
Dams hold numerous benefits for society through their ability to store water on a long-term basis. However, it is well-known that there is a detrimental effect of dams on the rivers that they impound, and this has been taken into account by the South African National Water Act (1998). The Act specifies a two component Reserve to provide a basic water supply to humans and to provide protection to downstream rivers and their associated ecosystems. From an ecological perspective, emphasis is now placed on ensuring that flow in rivers is maintained in a state that closely mimics the natural flow regime in order to sustain the water resource and its associated aquatic ecosystems. The resulting challenge for water resources modelling is to develop operating rule frameworks that can account for water supply to multiple users, including the "environment" which represents downstream aquatic ecosystems. These frameworks need to consider both water stored in dams, as well as water in the river which has been allocated to different water uscrs. Such an operating rule framework has been implemented ID the daily time-step ACRU agrohydrological model in order to: (a) satisfy the requirements of water users in general, (b) (c) include the environment as a user of water, and thus attempt to satisfy the water requirements of rivers and their associated ecosystems by making artificial releases from dams using both a simple and a complicated approach for determining the environmental requirements. The framework identifies four types of water users, each of which are capable of requesting water from a water source. These users are: a domestic user, representing the basic human needs component of the Reserve, an environmental user, representing the ecological component of the Reserve, an industrial user and an irrigator. The environmental user can generate water requests using either a simple or a complex environmental request method. The simple approach has proved to be oversimplified while the complex approach is capable of producing a flow regime downstream of a dam that closely mimics the natural flow regime. Two operating rules are employed to supply water to the four users, a generic dam operating rule, which considers water requested from a dam, and a channel operating rule, which considers water requested from a river. The two operating rules determine the amounts of water that each user can receive through the use of a curtailment structure, where abstractions made by users are limited, based on the storage level in the dam. Extensive validation of the framework has taken place and a case study was undertaken on the Pongola-Bivane river system which includes the Paris Dam in order to run various real-life scenarios. The results obtained show not only that the operating rule framework is functioning correctly, but that the use of a curtailment structure holds advantages for increasing assurance levels of the water users. There is also evidence to suggest that future possibilities exist for practical application of the operating rule framework to "everyday" dam operations.
Integrated water resources management studies in the Mbuluzi Catchment, Swaziland.
(2001) Dlamini, Dennis Jabulani Mduduzi.; Schulze, Roland Edgar.
Problems in the water sector range from degradation and depletion of water resources as a result of the impacts of land based anthropogenic activities, to the impacts of natural hydrological disasters and floods, while inadequate availability of water is at the core of most water related disputes in arid and semi-arid areas at local, regional, national and international levels. In the past, finding practical solutions for these problems fell neatly within the traditional scope of water resources management, which hinged almost entirely on economic viability of engineering oriented endeavors. However, a new set of management challenges has arisen following the high priority nowadays given to equity in water allocation and the protection of the natural environment above other issues. These new challenges have created a need for devising and adopting suitable management approaches, especially that would take social considerations into account. One of the approaches that provides promise relative to the new directions in dealing with contemporary water issues is integrated water resources management (IWRM). One objective of this study was to critically review the definitions and the fundamental principles of IWRM with the view of determining its applicability in developing countries and highlighting difficulties that may be faced regarding the adoption and implementation of this integrated approach. Swaziland is atypical example ofa developing country that is engulfed by the diverse water resources issues highlighted above and is currently engaged in updating water management legislation. Hence, Swaziland's experiences were used to put in perspective the key points and barriers regarding the adoption and implementation of IWRM. The catchment, the recommended spatial unit of IWRM, poses the first practical barrier, as catchments often cross both political and administrative boundaries, thereby creating the need for many water management problems to be solved across catchments with international security issues, cultural issues, different levels of development and different hydroclimatic regimes. The successful implementation of IWRM depends on effective participation of stakeholders. Lack of information flow between stakeholders of different backgrounds limits informed participation. Therefore, it is necessary to develop tools such as decision support systems (DSSs) that will foster easier multilateral information flow and aid decision making. IWRM requires information which itself should be managed in an integrated manner and be readily accessible. This is not always the case in developing countries with shortage of funds for data collection, manipulation and storage as well as adequately trained and experienced staff With the shortage of sufficiently long and reliable hydrological data for water management, the alternative is to synthesize records through hydrological modelling. Another objective of this study was to evaluate and test the suitability of the ACRU modelling system, a daily time-step agrohydrological model, to simulate catchment level hydrological processes and land use impacts as part of the assessment studies which form an integral part of integrated water resources management. ACRU was set up for the Mbuluzi, a 2958 km2 catchment in Swaziland. The catchment was subdivided into 40 sub catchments, after which the model was used for assessing both the impacts of land use and management changes on runoff yields and available water resources by evaluating present and future sectoral water demands, determining whether river flow from Swaziland into Mozambique meets the quantitative requirements of the international agreement existing between the two countries, and evaluating sediment yield and its spatial and temporal variation as well as its response to potential changes in land management. The physical-conceptual structure of the model, its multi-level adeptness regarding input information requirements, coupled with in-built decision support systems and generic default values make ACRU a suitable modelling tool in developing countries, as it makes it possible to obtain reasonable simulations for a range of levels of input information. Together with the model's multi-purpose nature, the ability of simulating ''what if scenarios", which was utilised in this study, makes it useful in the generation of information for IWRM. Future research needs which were identified include finding means of encouraging effective communication between scientists, water managers and other stakeholders, who may be "lay people". There is a need to conduct research that will lead to equipping ACRU with sediment routing and deposition algorithms, as well as routines to account more explicitly for dam operating rules and ecological issues, which would render its output even more useful in IWRM than the model's present structure allows.
Approaches to modelling catchment-scale forest hydrology.
(2002) Roelofsen, Aukje.; Jewitt, Graham Paul Wyndham.
South African commercial plantations occupy an estimated 1.5 million hectares of the country and as the demands for timber products increase, this area is expected to increase. However, further expansion is limited, not only by the suitability of land, but also by the pressures from other water users. As a result the need has arisen for simulation models that can aid decisionmakers and planners in their evaluation of the water requirements of forestry versus competing land uses at different spatial scales. Different models exist to perform such tasks and range from simple empirical models to more complex physically-based models. The policies of the National Water Act (1998) relating to forestry serve to highlight the requirements of a model used for the assessment of afforestation impacts and these are discussed in this document. There is a perception that physically-based distributed models are best suited for estimation of afforestation impacts on a catchment's water yield since their physical basis allows for extrapolation to different catchments without calibration. Furthermore, it is often stated that the model parameters have physical meaning and can therefore be estimated from measurable variables. In this regard, a review of physically-based modelling approaches and a comparison of two such hydrological models forms the main focus of this dissertation. The models evaluated were the South African ACRU model and the Australian topography-based Macaque model. The primary objective of this research was to determine whether topography-based modelling (Macaque model) provides an improved simulation of water yield from forested catchments, particularly during the low flow period, compared to a physically-based model (ACRU model) that does not explicitly represent lateral sub-surface flow. A secondary objective was the evaluation of the suitability of these models for application in South Africa. Through a comparison of the two models' structures, the application of the models on two South African catchments and an analysis of the simulation results obtained, an assessment of the different physically-based modelling approaches was made. The strengths and shortcomings of the two models were determined and the following conclusions were drawn regarding the suitability of these modelling approaches for applications on forested catchments in South Africa:• The ACRU model structure was more suited to predictive modelling on operational catchments, whilst the more complex Macaque model's greatest limitation for application in South Africa was its high input requirements which could not be supported by the available data. • Despite data limitations and uncertainty, the Macaque model's topography-based representation of runoff processes resulted in improved low flow simulations compared to the results from the ACRU simulations, indicating that there are benefits associated with a topographically-based modelling approach. • The Macaque model's link to the Geographic Information System, Tarsier, provided an efficient means to configure the model, input spatial data and view output data. However, it was found that the ACRU model was more flexible in terms of being able to accurately represent the spatial and temporal variations of input parameters. Based on these findings, recommendations for future research include the. verification of internal processes of both the ACRU and Macaque models. This would require the combined measurement of both catchment streamflow and processes such as evapotranspiration. For the Macaque model to be verified more comprehensively and for its application in operational catchments it will be necessary to improve the representation of spatial and temporal changes in precipitation and vegetation parameters for South African conditions.
Evaluation of a methodology to translate rainfall forecasts into runoff forecasts for South Africa.
(2002) Hallowes, Jason Scott.; Schulze, Roland Edgar.
South Africa experiences some of the lowest water resource system yields in the world as a result of the high regional variability of rainfall and runoff. Population growth and economic development are placing increasing demands on the nation's scarce water resources. These factors, combined with some of the objectives of the new National Water Act (1998), are highlighting the need for efficient management of South Africa's water resources. In South Africa's National Water Act (1998) it is stated that its purpose is to ensure that the nation's water resources are protected, used, conserved, managed and controlled in a way, which takes into account, inter alia, i. promoting the efficient, sustainable and beneficial use of water in the public interest, and ii. managing floods and droughts. Efficient and sustainable water resource and risk management can be aided by the application of runoff forecasting. Forecasting thus fits into the ambit of the National Water Act and, therefore, there is a need for its operational application to be investigated. In this document an attempt is made to test the following hypotheses: Hypothesis 1: Reliable and skilful hydrological forecasts have the ability to prevent loss of life, spare considerable hardship and save affected industries and commerce millions of Rands annually if applied operationally within the context of water resources and risk management. Hypothesis 2: Long to medium term rainfall forecasts can be made with a degree of confidence, and these rainfall forecasts can be converted into runoff forecasts which, when applied within the framework of water resources and risk management, are more useful to water resource managers and users than rainfall forecasts by themselves. The validity of Hypothesis 1 is investigated by means of a literature review. South Africa's high climate variability and associated high levels of uncertainty as well as its current and future water resources situation are reviewed in order to highlight the importance of runoff forecasting in South Africa. Hypothesis 1 is further examined by reviewing the concepts of hazards and risk with a focus on the role of effective risk management in preventing human, financial and infrastructural losses. A runoff forecasting technique using an indirect methodology, whereby rainfall forecasts are translated into runoff forecasts, was developed in order to test Hypothesis 2. The techniques developed are applied using probabilistic regional rainfall forecasts supplied by the South African Weather Service for 30 day periods and categorical regional forecasts for one, three and four month periods for I regions making up the study area of South Africa, Lesotho and Swaziland. These forecasts where downscaled spatially for application to the 1946 Quaternary Catchments making up the study area and temporally to give daily rainfall forecast values. Different runoff forecasting time spans produced varying levels of forecast accuracy and skill, with the three month forecasts producing the worst results, followed by the four month forecasts. The 30 day and one month forecasts for the most part produced better results than the more extended forecast periods. In the study it was found that hydrological forecast accuracy results seem to be inversely correlated to the amount of rainfall received in a region, i.e. the wetter the region the less accurate the runoff forecasts. This trend is reflected in both temporal and spatial patterns where it would seem that variations in the antecedent moisture conditions in wetter areas and wetter periods contribute to the overall variability, rendering forecasts less accurate. In general, the runoff forecasts improve with corresponding improvements in the rainfall forecast accuracy. There are, however, runoff forecast periods and certain regions that produce poor runoff forecast results even with improved rainfall forecasts. This would suggest that even perfect rainfall forecasts still cannot capture all the local scale variability of persistence of wet and dry days as well as magnitudes of rainfall on individual days and the effect of catchment antecedent moisture conditions. More local scale rainfall forecasts are thus still needed in the South African region. In this particular study the methods used did not produce convincing results in terms of runoff forecast accuracy and skill scores. The poor performance can probably be attributed to the relatively unsophisticated nature of the downscaling and interpolative techniques used to produce daily rainfall forecasts at a Quaternary Catchment scale. It is the author's opinion that in the near future, with newly focussed research efforts, and building on what has been learned in this study, more reliable agrohydrological forecasts can be used within the framework of water resources and risk management, preventing loss of life, saving considerable hardship and saving affected industry and commerce millions of rands annually.
Predicting emissions using an on-road vehicle performance simulator.
(2002) Govindasamy, Prabeshan.; Lyne, Peter William Liversedge.
South Africa is coming under increasing pressure to conform to the rest of the world in terms of emissions regulations. The pressure is caused by a number of factors: international organisations requiring local companies to adhere to environmental conservation policies, evidence from within South Africa that efforts are being made to reduce environmental pollution in line with other countries and keeping abreast of the latest technologies that have been incorporated into vehicles to reduce emissions. In light of these problems associated with emiSSions, a study was initiated by the Department of Transport and the School of Bioresources Engineering and Environmental Hydrology at the University of Natal to investigate and develop a method of predicting emissions from a diesel engine. The main objective of this research was to incorporate this model into SimTrans in order to estimate emissions generated from a vehicle while it is travelling along specific routes in South Africa. SimTrans is a mechanistically based model, developed at the School, that simulates a vehicle travelling along a route, requiring input for the road profile and vehicle and engine specifications. After a preliminary investigation it was decided to use a neural network to predict emissions, as it provides accurate results and is more suitable for a quantitative analysis which is what was required for this study. The emissions that were predicted were NOx (Nitric oxide-NO and Nitric dioxide-N02), CO (carbon monoxide), HC (unbumt hydrocarbons) and particulates. The neural netWork was trained on emissions data obtained from an ADE 447Ti engine. These neural networks were then integrated into the existing SimTrans. Apart from the neural network, an algorithm to consider the effect of ambient conditions on the output of the engine was also included in the model. A sensitivity analysis was carried out using the model to prioritise the factors affecting emissions. Finally using the data for the ADE 447Ti engine, a trip with a Mercedes Benz 2644S-24 was simulated using different scenarios over the routes from Durban to Johannesburg and Cape Town to Johannesburg in South Africa to quantify the emissions that were generated.
Towards improved parameter estimation in streamflow predictions using the ACRU model.
(2002) Royappen, Marilyn.; Schulze, Roland Edgar.
An unresolved problem in hydrology has been to establish relationships between catchment attributes and the flow characteristics of the stream. Such information is commonly sought to improve streamflow predictions, often in a process of extrapolating research results obtained from relatively few, but intensively studied catchments, to a broader region. This study has attempted to clarify terminology related to streamflow generation processes and mechanisms, and to investigate relevant physiographic and climatic characteristics which critically influence the hydrological responses of catchments. Fourteen catchments were selected for this study. They comprised both operational and research catchments. These catchments were selected to be representative of variations in climate, topography, vegetation and geology occurring throughout the Republic of South Africa (RSA). The selection of catchments was also restricted to areas less than 100 krrr', and to the higher rainfall regions of the country, where runoff is significant and any land use changes may lead to marked changes in evapotranspiration and streamflow. A catchment was also selected from an arid zone in the USA, to capture the flow characteristics that are typical of such areas. A frequently applied simulation model on RSA catchments is the ACRU model. While physical-conceptual in structure it contains some parameters which, while not determining total streamflow magnitudes, governs the time distribution of the streamflows generated. Two such parameters from the ACRU model selected were the coefficient of baseflow response (COFRU) and the quickflow response fraction of the catchment (QFRESPj. These parameters are not explicitly physically based, and therefore improved guidelines of initial parameter values are required. Relationships between catchment characteristics and these two parameters were sought to provide guidelines for effective parameterisation of these parameters in future studies. Trends between QFRESP and COFRU, and catchment physical and climatic attributes such as catchment area, average depth of the soil profile, maximum basin relief, MAP and profile plant available water were identified, and could prove useful to future users of the ACRU model and guide experimentation in estimating initial parameter values. However, only a single significant multiple regression model was obtained for the baseflow release fraction COFRU from a catchment using MAP, catchment area and profile plant available water.
Developing a real time hydraulic model and a decision support tool for the operation of the Orange River.
(2002) Fair, Kerry.; Pegram, Geoffrey Guy Sinclair.
This thesis describes the development of a decision support tool to be used in the operation of Vanderkloof Dam on the Orange River so that the supply of water to the lower Orange River can be optimised. The decision support tool is based on a hydrodynamic model that was customised to incorporate real time data recorded at several points on the river. By incorporating these data into the model the simulated flows are corrected to the actual flow conditions recorded on the river, thereby generating a best estimate of flow conditions at any given time. This information is then used as the initial conditions for forecast simulations to assess whether the discharge volumes and schedules from the dam satisfy the water demands of downstream users, some of which are 1400km or up to 8 weeks away. The various components of the decision support system, their functionality and their interaction are described. The details regarding the development of these components include: • The hydraulic model of the Orange River downstream of Vanderkloof Dam. The population and calibration of the model are described. • The modification of the code of the hydrodynamic engine so that real time recorded stage and flow data can be incorporated into the model • The development of a graphical user interface to facilitate the exchange of data between the real time network of flow gauging stations on the Orange River and the hydraulic model • The investigation into the effect of including the real time data on the simulated flows • Testing the effectiveness of the decision support system.
The hydrosalinity module of ACRU agrohydrological modelling system (ACRUsalinity) : module development and evaluation.
(2003) Teweldebrhan, Aynom Tesfay.; Lorentz, Simon Antony.; Schulze, Roland Edgar.
Water is characterised by both its quantity (availability) and its quality. Salinity, which is one of the major water quality parameters limiting use of a wide range of land and water resources, refers to the total dissolved solutes in water. It is influenced by a combination of several soil-water-salt-plant related processes. In order to develop optimum management schemes for environmental control through relevant hydrological modelling techniques, it is important to identify and understand these processes affecting salinity. Therefore, the various sources and processes controlling salt release and transport from the soil surface through the root zone to groundwater and streams as well as reservoirs are extensively reviewed in this project with subsequent exploration of some hydro salinity modelling approaches. The simulation of large and complex hydrological systems, such as these at a catchment scale, requires a flexible and efficient modelling tool to assist in the assessment of the impact of land and water use alternatives on the salt balance. The currently available catchment models offer varying degrees of suitability with respect to modelling hydrological problems, dependent on the model structure and the type of the approach used. The A CR U agrohydrological modelling system, with its physically-conceptually based characteristics as well as being a multi-purpose model that is able to operate both as a lumped and distributed model, was found to be suitable for hydro salinity modelling at a catchment scale through the incorporation of an appropriate hydro salinity module. The main aim of this project was to develop, validate and verify a hydro salinity module for the ACRU model. This module is developed in the object-oriented version of ACRU, viz. ACRU2000, and it inherits the basic structure and objects of the model. The module involves the interaction of the hydrological processes represented in ACRU and salinity related processes. Hence, it is designated as ACRUSalinity. In general, the module is developed through extensive review of ACRU and hydrosalinity models, followed by conceptualisation and design of objects in the module. It is then written in Java object-oriented programming language. The development of ACRUSalinity is based mainly on the interaction between three objects, viz. Components, Data and Processes. Component objects in ACRU2000 represent the physical features in the hydrological system being modelled. Data objects are mainly used to store data or information. The Process objects describe processes that can take place in a conceptual or real world hydrological system. The Process objects in ACRUSalinity are grouped into six packages that conduct: • the initial salt load determination in subsurface components and a reservoir • determination of wet atmospheric deposition and salt input from irrigation water • subsurface salt balance, salt generation and salt movement • surface flow salt balance and salt movement • reservoir salt budgeting and salt routing and • channel-reach salt balancing and, in the case of distributed hydro salinity modelling, salt transfer between sub-catchments. The second aim of the project was the validation and verification of the module. Code validation was undertaken through mass balance computations while verification of the module was through comparison of simulated streamflow salinity against observed values as recorded at gauging weir UIH005 which drains the Upper Mkomazi Catchment in KwaZuluNatal, South Africa. Results from a graphical and statistical analysis of observed and simulated values have shown that the simulated streamflow salinity values mimic the observed values remarkably well. As part of the module development and validation, sensitivity analysis of the major input parameters of ACRUSalinity was also conducted. This is then followed by a case study that demonstrates some potential applications of the module. In general, results from the module evaluation have indicated that ACRUSalinity can be used to provide a reasonable first order approximation in various hydrosalinity studies. Most of the major sources and controlling factors of salinity are accommodated in the ACRUSalinity module which was developed in this project. However, for a more accurate and a better performance of the module in diversified catchments, further research needs to be conducted to account for the impact of salt loading from certain sources and to derive the value of some input parameters to the new module. The research needs include incorporation in the module of the impact of salt loading from fertilizer applications as well as from urban and industrial effluents. Similarly, further research needs to be undertaken to facilitate the module's conducting salt routing at sub-daily time step and to account for the impact of bypass flows in heavy soils on the surface and subsurface salt balances.

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