Water is the most abundant of the natural resources and is more often than not taken for granted. It is only when it manifests its excesses in the form of crippling droughts and devastating floods that much more attention is paid to it. People simply take it for granted that clean, disease-free water will gush from a lap when they open it. Which other of life's necessities is delivered into the very room in which you require it, at some 60 cents per tonne retail, and that after it has been treated and often been transported over tens, if not hundreds of kilometres, over hill and through dale. All this is made possible through the efforts of the engineers and scientists who devote their professional career to this life-giving liquid, this great cleanser, this universal solvent. Not everybody is so appreciative of it though. Not the hobo at Joubert Park, who had tried brandy and water, whisky and water, gin and water, blue train and water - they all gave him a hangover, so it must have been the water!
The dolos breakwater armour unit was developed by the late Eric M Merrifield when he was harbour engineer at East London. The need arose when, in 1963. approximately 60 per cent of the 37 t rectangular concrete blocks used to protect the seaward side of the East London breakwater had disappeared and major repair works were called for. It was obvious that repairing the breakwater with similar blocks would be ineffective unless they were made significantly heavier. This would have caused serious construction problems in that the available crane could not handle such blocks.
It was some forty-five years ago that a paper appeared in the Minutes of Proceedings of the South African Society of Civil Engineers entitled 'The dissipation of energy of a flood passing over a high dam'1. The author was Lt Col D F Roberts, and the paper on the Loskop Dam splitters covering some 46 pages of text commanded much attention and drew eight discussions. which with the author's reply added another 34 pages to the annals of our profession. In subsequent years Col Roberts' ideas, first applied to the Loskop Dam in 1937 in the form of splitters to partly dissipate the energy of the overflowing sheet of water before it struck the downstream face ledge on which the future raising of the dam was to be accommodated (see postscript), were to be emulated on some 32 dams in Southern Africa and abroad. The application was internationally recognized when Sir Alexander Gibb and Partners used it for the design of the Hendrik Verwoerd and P K le Roux Dams' spillways and later for the Victoria Dam in Sri Lanka2.
All but about 15 per cent of the exploitable surface water resources of Southern Africa are conveyed in rivers of which the waters have to be shared with neighbouring sovereign, national or self-governing slates. Only in parts of the Cape Province are rivers found that flow their full length within the boundaries of the Republic. It follows that international and inter-state co-operation in water resource development is imperative.
The greater part of South Africa is semi-arid, having a mean annual rainfall of 500 mm, which is only 60 per cent of the world average. River flow is poorly distributed relative to areas experiencing economic growth. Hydrological extremes, in the form of droughts and floods, are common. Over large areas the limited ground water is saline. Transported sediment deposited in storage dams reduces their combined capacity by the equivalent of a medium-sized reservoir each year. Incremental investments in dam development show diminishing returns because of factors such as long carry-over periods under high evaporation rates, increasing salination and the need for longer transmission lines and high pumping heads. Accordingly, unit costs of supply are expected to rise. Against this background, the populations of the less modern sector of South Africa as well as of several neighbouring states are increasing rapidly, while the developed economy requires increasing assurance of water supply and higher quality. Water is already scarce in many parts of the country and shortages have become critical during droughts. Augmentation of water schemes involves large capital investments and in most cases international co-operation.
Water is arguably South Africa's most precious natural resource. Research and investigations have shown that groundwater resources in South Africa are relatively meagre. South Africa's major water supplies are and will probably always be derived mainly from surface resources. South Africa's climate is semi-arid with an average rainfall of 475 mm/a, compared with 735 mm for the USA and 860 mm for the world as a whole.1 In South Africa about nine per cent of the precipitation, ie 43 mm or about 52.109 m3/a, reaches the river systems as runoff. The economically exploitable proportion of this is estimated at 34.109 m3/a, ie 67 per cent of the total. It is predicted that all of this will be fully exploited by the year 2020.2
Owing to the lack of perennial streams in the semi-arid to arid parts, two-thirds of South Africa is largely dependent on ground water. In terms of total water consumption, ground water contributes only about 13 per cent However about 105 towns across South Africa are totally dependent on ground water. Ground water consumption amounted to 1 800 million m3 in 1980 and may grow to about 5 000.106 m3 in the next two to three decades.1 The major users are: Urban use, including industrial and mining use 4% Rural domestic use 7% Stock-watering 6% Irrigation 78% Mining and Quarries 5%
It is already well known that by early next century rising demand on South Africa's conventional surface and ground water resources will cause water shortages to be severe and frequent. Available data on water in the atmosphere suggests that approximately 6.1012 m3 of water, mainly in vapour form, is transported annually over the South African land mass. This is ten times the volume that will, on average, reach the surface of South Africa as natural precipitation. The rest is destined never to reach the ground. even though it may appear temporarily in the form of droplets or ice particles in clouds. If an additional one per cent of the water in the atmosphere could be induced to precipitate at ground level, this would increase rainfall by 10 per cent, equivalent in volume to the mean annual runoff in all of South Africa's rivers. Widespread benefits, not only for runoff, but also for dryland agriculture and forestry, are instinctively suggested.
Gedurende die eerste helfte van hierdie eeu was waterbronbeplanning in Suid-Afrika relatief ongekompliseerd. Ondersoeke was gewoonlik op enkel projekte toegespits, ontwikkeling was hoofsaaklik landbou-gerig en behoeftes was oor die algemeen klein in vergelyking met die ekonomies benutbare waters wat in die opvanggebiede voorgekom het. Ook in die buurstate om Suid-Afrika, wat riviere met ons gedeel het, kon ontwikkeling voortgaan met min nodigheid vir skakeling oor-en-weer. Die Departement van Waterwese (voorheen die Departement van Besproeing) was die enigste instansie met magte om waterbronne te beplan en te beheer soos deur wetgewing bepaal (die Waterwet, 1956),
The erratic nature of South Africa's climate is well known but what is often not fully realized is that as river systems are developed the inconsistency of the remaining unutilized runoff is much higher than the base-flow. To utilize this water requires larger dams, longer carry-over periods with more evaporation losses and - most importantly - greater risks of shortages (see Fig 1). In addition, as basins become more developed and more dams are built, the interdependence of sources such as dams, groundwater basins and re-usable water increases greatly. In this context water quality is also of increasing importance.
Stochastic hydrology is the study of the application of stochastic processes (their descriptionption, measurement, estimation and simulation) in engineering hydrology, which in itself is the study of the harnessing of water resources in the service of mankind. The term 'stochastic process' descriptionbes a random process observed discretely or continuously in time (or more unusually space). The essential character of a stochastic process is that the order in which events occur is important, in fact is an essential aspect of the phenomenon. This is because it is quite likely that there is a dependence structure in the process that it is important to measure and effectively preserve in any descriptionption or simulation. Typical examples of stochastic processes are the sequence of wet and dry days as measured by a rain-gauge or the arrivals of telephone calls at an exchange.
The impact of catchment developments on hydrology and water resources is rapidly becoming a major consideration when analysing flow data in South African rivers. In recent years such developments have become more widespread and interbasin transfers in particular have become very important. Fig 1 provides an indication of the magnitude of water transfers in and around the Vaal Dam catchment. With the exception of the Lesotho Highlands transfer, all of the transfer schemes indicated are currently in use. This shows that the natural inflow to the Vaal Dam of approximately 2 000.105 m3/a is already augmented by Over 800.105 m3/a by the year 2020 when the final phase of the Lesotho Highlands scheme is scheduled for completion. The values shown in Fig 1 refer to interbasin transfers that represent only one of many possible developments in a catchment. There are numerous other forms of development that can influence the water resources of an area, some of which will be discussed in subsequent sections.
Biotechnology may be defined as the integrated use of biochemistry, microbiology and the engineering sciences to achieve industrial application of the capacities of microbes and cultured tissue cells. Environmental biotechnology, which may involve integration with non-biological technologies, is the specific application of biotechnology to the management of environmental problems, including waste treatment and pollution control.