|United Nations University - Work in Progress Newsletter - Volume 12, Number 1, 1989 (UNU, 1989, 12 pages)|
|Sustaining the Earth|
|Anticipating global trends: Aspects of UNU work for the period 1990-1995|
|'An uncontrolled global experiment...'|
|'A little breathing space': Report from the Budapest|
|Energy savings: Sooner much better than later|
|'The rich get richer...'|
|Old wine in new bottles?|
|Tectonics of the desert cities|
|Man in the mangroves|
|Diverting the Nile|
|Losing the soils of Africa|
|In fairness to the future|
By Mahmoud Abu-Zeid
The events leading up to the building of the Aswan High Dam in Egypt are an important part of the political history of our time, particularly the dismemberment of the colonial system. Equally, the dam's environmental history, since it was completed in 1971, could have far-reaching consequences. The river control imposed by the dam has eliminated annual flooding of the Nile, which over the millennia helped determine the life cycles and religious beliefs of Egypt's farmers as well as the fertility of the soil they tilled. This change raises the issue of what happens when concern about the environment and development needs appear to clash. Consequently, it also reinforces the argument for scientifically sound ecological monitoring procedures. In the following selection, Mahmoud Abu-Zeid, Chairman of the Water Research Centre, Ministry of Irrigation, Cairo, discusses the need for the construction of the High Dam and reviews some of its major environmental impacts. The excerpt is taken from his contribution to the volume. Environmental Impact Assessment for Developing Countries, edited by Asit K. Biswas and Qu Geping. The book reports the proceedings of a 1983 workshop in Guangzhou, China, on environmental impact monitoring, which the UNU co-sponsored with the International Society for Ecological Modelling and the United Nations Environment Programme. - Editor
No dam can be built and no lake can be created without environmental alteration of some kind. Development projects along the River Nile have been primarily conceived for the purposes of water conservation, agriculture, flood control, power generation and navigation. As in most other river development programmes, the main emphasis has been on the optimization of the hydrological system, with little consideration for the environmental implications which could result from changes in the biological, climatic and hydrogeological regimes.
In Egypt, the construction of the Aswan High Dam has caused modifications in the hydrological regime of the river. River flow control has eliminated the Nile flood which used to flush and cleanse the river once a year. Meanwhile, the impoundment of water has caused some changes in the water quality with regard to it physico-chemical and biological properties. Simultaneously, with increasing domestic, agricultural and industrial activities, the quantities of effluents requiring treatment and disposal are increasing. The complexities of waste treatment, in some circumstances, are demanding the use of advanced techniques and requiring increasing expenditure.
The Need for the High Dam
The discharge of the River Nile is subject to wide seasonal variations. About 80 per cent of the total annual discharge occurs during the flood season of August to October; the remainder is spread over the rest of the year. About 85 per cent of this annual discharge originates in Ethiopia, and 15 per cent in the lake plateau in central Africa. The White Nile rises from this plateau and is the main source of water to the Nile valley during the low-flow summer period. The seasonal summer flow was the limiting factor for perennial irrigation in Egypt.
The first attempt to store flood water during the low-flow period took place in 1902, when the old Aswan dam was constructed. Its capacity at that time was some 10 billion cubic metres. The old dam was subsequently heightened twice to reach a capacity of 50 billion cubic metres in 1934.
Apart from the seasonal variation in the discharge of the Nile, the total annual discharge is subject to wide fluctuations from year to year. The highest flow recorded was 1.54 trillion cubic metres in 1878; the lowest was only about a quarter of that, 420 billion cubic metres recorded in 1913. Thus the short-term subannual storage proved to be inadequate in low years for irrigation. Long-range storage was the only solution. A suitable location for the long-term reservoir was found to be at Aswan. The High Dam was constructed to guarantee a constant annual draft of 840 billion cubic metres - of which 555 billion was for the benefit of Egypt and 185 billion was for Sudan. The High Dam is of rock-fill type and was constructed 7 km south of the city of Aswan. The total length of the dam is 3,600 m, of which 520 fall between the two Nile banks, and the rest extend along its two sides. The height of the dam is 111 m above the river bed. Its width is 980 m at the bottom and 40 m at the top.
Water Quality Issues
Since the construction of the Aswan High Dam, studies have been carried out on how best to use its reservoir - Lake Nasser - to provide timely water to meet overall demand. Some attention has been also given to the biological aspects of the new lake environment.
The complex environment transformation cannot be ignored in the management of the reservoir constructed for economic development. The region around the lake is a potential area for land reclamation and new settlements, urgently needed by Egypt's expanding population. This is likely to have a profound effect on the reservoir ecosystem and downstream river conditions.
The natural water body of the lake responds differently depending on the nature of the inputs to the system which affect water quality. These inputs can be divided into two categories. Firstly, the natural inputs, such as rainfall, solar radiation, runoff and winds, which, in conjunction with the surface and groundwater characteristics of the basin, determine the background quality of the water. Secondly, the system is subjected to a variety of man-made effects, such as wastewater discharges or water diversions due to industrialization, urbanization and agricultural developments.
As with other man-made reservoirs. Lake Nasser has a long narrow shape, extending south of Aswan for about 500 km, 200 km of which are within Sudan. The mean width of the lake is 10 km, but there are considerable variations along its course. Variations in the size and shape of the reservoir are obviously affected by the annual and over-year operation policy of the dam. With different operating rules, an annual variation in the water level of 5 to 10 m is highly probable; fluctuations over a period of years can be as much as 30 m. These variations are very important because they correspond to substantial changes in the surface area of the reservoir.
The variations in the water levels have important implications for the mixing of the lake and the distribution of the water arriving with the seasonal flood; this water carries a large sediment load which is deposited in different locations of the reservoir, depending upon the level of the lake before the arrival of the flood and the size of the flood.
At selected locations in the reservoir, frequent measurements are carried out for water temperature profiles, light intensity distribution, nutrients concentration (including phosphorus and nitrogen), and chlorophyll concentration.
The main effects of water impoundment in the Aswan High Dam reservoir are changes in siltation, salinization, thermal stratification and hydrobiological characteristics. Long-term geomorphological changes due to siltation, for example, will undoubtedly affect the reservoir's water quality and ecosystem characteristics. These effects will be more noticeable in the long run, after a significant change in the reservoir's configuration has taken place.
The Aswan High Dam reservoir, in general, exhibits high rates of biological production. Phytoplankton and zooplankton distribution exhibits different seasonal variations in different sectors of the lake. Cyanophyta, the undesirable blue-green algae predominant in the northern sector of the reservoir, are typical impoundment organisms. They are generally capable of nitrogen fixation and represent a dead end in the food chain. In addition, they cause taste and odor problems.
Extensive investigations have been conducted on the fish in the reservoir. Fish distribution and abundance vary among the different sectors. The migration of certain types of fish has been dependent on the arrival of the turbid flood water and their preference for riverine or semi-riverine conditions. Fish behavioural changes partially account for the differences in their contribution to the catches, which is quite significant for species of economic importance in commercial fisheries.
Risk in Economic Development
Since the dam's construction, there have been a number of plans drawn up by several agencies for the economic development of the region along the shores of the reservoir. This includes the establishment of human settlements (e.g. irrigation, land reclamation), industrial development, and tourism and recreational programmes.
The big risk is that such development schemes will affect water quality and the aquatic ecosystem of the reservoir. Furthermore, the deterioration of the quality of the reservoir will affect downstream river uses, since the reservoir is the only source of the Nile water in Egypt.
A serious consequence could be the propagation of the disease, schistosomiasis, and the northward migration of the malaria mosquito carrier from Sudan. The mosquito Gambia has invaded Egypt on several occasions, the last being in 1942. The small carriers from both types of schistosomiasis have already been found in the reservoir. The assumption is that the fishermen brought the disease with them to the region.
Policy-makers should consider the alternative of keeping the reservoir area largely free from human activities, i.e. as a restricted and protected area, in an attempt to avoid possible pollution problems and the spreading of water-borne diseases. Alternative plans for the development of the shore of the reservoir should incorporate more realistic assessments of the environmental impacts and the cost of pollution control.
Water Quality Downstream
Despite the availability of sufficient legislation for water pollution control in Egypt, a variety of industrial waste effluents and runoffs are frequently discharged directly into the Nile at some locations along the river and its main tributaries. The most significant and potentially dangerous pollution effect is due to waste discharge from industries. The significance of the Aswan High Dam in this is that the absence of annual floods (due to long-term storage in the reservoir) means that the chance for annual cleaning of the Nile waters is very much restricted.
The Nile Delta
The Nile delta is the result of silt deposition in the Mediterranean since prehistoric time. The northern coast has assumed its present shape since ancient times. This coast has defended itself against wave attack, storms, sea and coastal currents and maintained a quasidynamic equilibrium under differing meteorological conditions. Yet observations since 1898 indicate the presence of erosion of the seashore in some locations at Rosetta and Damietta. Some scientists believe that recent erosion is due to the change of the Nile regime caused by the construction of the Aswan High Dam and the decrease of silt releases to the Mediterranean. This possibility is presently being studied through a programme of topographical, geological, morphological, sedimentation, erosion and sea current surveys.
During the planning and construction of the Aswan High Dam in the 1960s, environmental impact assessment did not play a major part. This, however, was the normal state of affairs at that time, not only in Egypt but also in other countries. With increasing environmental awareness, steps have been taken to monitor the impacts of the dam and to take appropriate remedial actions whenever necessary.