The importance of dams

Mankind already uses the cultivation of water resources since 4 millennia to provide for the necessities of life. The practice of storing large water quantities with dams started with ancient Mediterranean cultures. The first record of a dam dates back to 2550 b.c., with the completion of the Sadd el Kafara project in Egypt. The beginning of dam construction coincides with a trend towards a sedentary lifestyle: in the first large settlements, local water needs suddenly increased significantly. And since the natural supply of water, through the interplay of wet and dry periods varies seasonally, its supply can also be secured through the storage of water in large reservoirs.

With such useful, regional water management, one can realise multi-purpose projects, using hydropower for generating mechanical and electrical energy, for the protection against flood threats, the gradual release of water downstream for navigation to ensure adequate minimum water flow (raising the low water level), and finally the delivery of adequate quantities of process water and drinking water for industry and population, for leisure time and recreation. Further applications are the accumulation of ground water, the creation of fish farms and irrigation in agriculture, particularly in tropical countries. World-wide, there are approximately 46 000 (earth-fill and masonry) dams of height 15 meters and above, of which 70% are used for irrigation of cultivated land, and their share is expected to increase by 15% in the coming decades through new construction. According to a world-wide statistic, there is about 3.2 billion ha land usable for agriculture, from which at present roughly half is being used. The water volume stored by dams is approximately 7000 m3, equivalent to about one fiftieth of the water volume transported annually by the world's rivers. Over 100 dams achieved construction heights in the range above 150 meter and up to 330 meter.

Considering that world population has exceeded 6 billion people in 2002 (growing annually by 70-80 million), and that 20% suffer from chronic water shortage, and that 2.6 billion people have no access to any sanitary facilities, one can only conclude that there is unmistakably an upcoming crisis for an adequate water supply, food supply and healthcare. Every day, 6 000 people die because of lack of water. According to the latest UN goals, 0.6 billion people should be relieved from this situation by 2015. In addition, by 2030, two thirds of all people will live in cities, and mankind will need 55% more food. This crisis can only be met by an economy using larger water quantities with improved quality, through the construction of more dams. At the same time, in coastal areas, a substantial use of sea water will probably be necessary to meet the increasing needs of mankind.

Pros and cons of dams

Dams are very demanding structures. They are the result of outstanding engineering performance, and represent mankind's cultural development, excellent civil engineering and technology that has been developed over a span of several millennia.

Today, dams are often considered from a critical angle. This includes horror stories about their negative social and ecological effects. These effects can and should be avoided - or at least minimised - by comprehensive investigations and appraisals.

Designs need to take into consideration many local conditions: technology, finance and economic efficiency on the one hand, water management, economic necessity, environmental performance and the cultural, social and political context on the other. Only in this manner can a project which has many diverse effects be aligned across various disciplines. All affected and interested in the project need to be involved, with the common goal to preserve the vital good 'water' and to use it in an intelligent and balanced way, considering the environmental interests for man, plants and animals, while facilitating and enriching human existence.

Measures to limit negative effects on the environment

Above problems are handled since a long time by multiple professional bodies, such as for example the International Commission on Large Dams (ICOLD) founded in 1928, supported by 82 member countries, and the World Commission on Dams, initiated in 1997 by the World Bank. Substantial publications and regulations cover a.o. the relocation of population living in the area of the future reservoir, and the maximum preservation, and in some cases even improvement, of the living conditions, local communities, economic power, cultural facilities and social surroundings, including as well equivalent landscape and agricultural conditions. In this context, the economic advantages of a dam and its applications should not only benefit the economy at large, but in proportion also the indigenous population, through far-reaching compensation investments. Equally essential is the promotion of training centres, crafts and industry.

To give a quantitative benchmark in this context, for a dam primarily used for electricity generation, the world bank offers a guideline of minimum 5 kW per ha future flooded area, and 7 kW per relocated inhabitant. Accordingly, a flooded area of 260 000 ha and relocation of 200 000 persons is considered acceptable when considering the incontestable advantages of a dam with an installed hydropower of 1 300 Megawatt (1.3 million kW), that can generate electricity equivalent to half a nuclear station with the same power rating.

In tropical countries, the sanitary and health aspects surrounding a dam receive special importance. The appearance and spread of diseases related to slack water zones needs to be prevented through an operation mode that changes the water level continuously, through improvement of hygienic conditions in homes and courtyards and through medical precautions.

Disturbances to fauna and flora through the storage and hence removal of natural flow conditions downstream can be mitigated through an adequate and dynamic water management. Modern computation methods, considering hydraulics, morphology, fauna and flora, enable the optimisation of boundary conditions for an extensive conservation of the original ecology. Hereby, the interplay of low water and high water regimes, of temporary flooding and draining downstream areas, as well as the required water quantities throughout the year for plants and marine life are simulated and translated into operating manuals for the dam.

An additional problem is the assessment of a dam is the deposit of till and fine-grained soil material, i.e. sedimentation and silting at the expense of the reservoir. As an indication, one must expect to loose annually about 1% of the volume of the reservoir because of sedimentation. Using a basin before the reservoir, large grain impurities of the incoming river water could be forced to deposit through lowering the water speed. This pre-basin could then be dredged at intervals, and the aggregate put to use, depending on the type of mineral. On the other hand, fine-grain suspended materials in the dam water, that deposit much more slowly in the main reservoir, could be useful - depending on their origin - as nutritious sediments for improving water quality and bio-diversity. They maintain this benefit in the tail water as well. Countermeasures to limit the amount of till and suspended matter caused by erosion and removal are offered by reinforced growing and reforestation in the area.

For the quality of the stored water, it is of prime importance to clear entirely the future reservoir, in particular the removal of organic material such as plant layers, humus layers, root sets and stock of trees, in order to avoid decomposition processes. This also applies to the removal of suspended matter during dam operation.

For the planning, development and operation of dams, safety procedures are indispensable, and currently standard. These are reflected in the long-term, ever recurring monitoring of deposits and drain, till management and sedimentation, high water events and high water drain. Extensive, regular measurements of the stability of the constituent structures, and of the mountain sides and embankments of the dam, as well as continuous monitoring of the functional efficiency of technical installations are needed. Ageing phenomena and renovation measures need to be pursued as well as risk assessments and protection measures for settlements, buildings and roads downstream. This includes the development of emergency plans, and the technical instruction of regulatory authorities concerned on subjects such as multi-purpose dam operation, operating procedures, the importance of environmental protection and health precautions for the local population, in particular in areas with hot climates.

Dams are more than ever indispensable for an appropriate water provision, and an essential component of the human cultivated landscape. The interdisciplinary cooperation of professionals from engineering, natural sciences, economics and the humanities is as much a matter of course as strong communications and awareness building in broad layers of population.

Excellent examples of multi-purpose facilities

Assuan dam

We list the Assuan dam on the Nile in Upper Egypt as a first example of a multi-purpose application of a large dam, that has often been discredited. After the 1967 completion of the 'high dam', it covered 3 years later a third of Egypt's electricity consumption through hydro power. With an installed capacity of 2 100 MW, it can produce at most 15.1 billion kWh per year. The 111 m high and 3 820 m wide stone dam retains a 500 km long reservoir, reaching into the Sudan, with a storage volume of 169 billion m3. Of this volume, 26 billion m3 serves for avoiding high water conditions and 31 billion m3 for the long-term disposal of sediments. By far the major part of the water stored is used for irrigation and provision of drinking water to the rapidly growing population.

This dam is one of the most often investigated, discussed and documented multi-purpose facilities. The positive and negative aspects are profoundly interlinked. These include riverbed erosion underneath the dam, the loss of nutritient-rich mud for soil regeneration in agriculture or for production of bricks, health risks resulting from the reduced water distribution, and increased slack water areas in the river valley and finally increasing soil salinisation. Through targeted countermeasures, meanwhile, an optimum has been achieved of the positive effects, which includes the control of multiple dry periods and extreme high water events.

Itaipu hydropower station

This facility near the world's most famous cascades started operation in 1983 and was the largest hydropower station at the time. The power station on the Parana river is operated jointly by Brazil and Paraguay. The dam consists of a concrete wall and rockfill. It is 196 m high and 7.3 km long at the highest point. It enables storing 29 billion m3 of river water. The installed power is 12 600 MW, with 18 turbines. Other functions of this multi-purpose project are the support of navigation in low water regime, and proportional flood control.

Storage power station Atatürk

The river storage power station Atatürk on the Eufrates in Turkey, completed in 1992 after 10 years of construction, is a multi-purpose project for hydropower production, agricultural irrigation and flood control. The dam is 169 m high and 1.66 km long, with rockfill. It creates a reservoir of 48.7 billion m3, enabling operation of a hydropower station of 2 400 MW and irrigation of 1 million hectares of agricultural land.

3-Gorges project

In 1992, the Chinese People's Congress granted permission for the construction of the world's largest river storage power plant, located in the middle reaches of the Jangtse river, the m3 longest river on earth. This venture, conceived as a multi-purpose project, will ensure - in addition to high quality energy generation - a highly effective 100-year protection against the ever recurring floods (last event in 1998 with 1 600 casualties) as well as navigation of large ships from the YellowSea 3000 km land inward. The total volume of the 632 km long, 1.1 km wide river reservoir run will be 39 billion m3 - high water containment accounts for 22 billion m3 of this. The maximum reservoir surface will be 1 045 m3, flooding 990 m3 of land.

The river dam is a 181 m high, 2.3 km long concrete wall. At the base of the dam, a hydropower station in 2 sections, 600 m each, with 26 generating sets of 700 MW each for a total capacity of 18 200 MW will be constructed. Annual electricity production will be 84.7 billion kWh, representing about one sixth of German's annual electricity needs. According to the latest plans, a third power plant with 6 generating sets of 700 MW each will be added on the right bank, bringing total installed power to 22 400 MW.

Shipping traffic has a 5-stage lock and a ship's elevator with 115 m stroke height at its disposal. The 3-Gorges project required a considerable social restructuring of the surrounding industrial centres and many settlements. Resettlement alone affected 1.3 million people, for which - irrespective of psychological problems, completely new towns and villages with agricultural land have been constructed in neighbouring regions. Even while old temples and monuments are being preserved, a series of delightful landscapes and historic treasures will be lost in the flood.

The controlled annual water throughput is 960 billion m3. A particular till and sediment management ensures the most comprehensive possible control for the 380 million m3 estimated annual volume of solids during high and low water regimes, under different storage and drainage conditions .

Without a doubt, the region's economic power will improve significantly, through the disposal of large quantities of environmentally friendly energy. Current electricity production, mainly coal-based, can be reduced. The resulting saving of 50 million tonne coal per year corresponds to 100 million tonne C02 saved, and well as several thousand tonne SO2, CO and nitrogen oxides. Finally, recreational activities and tourism will experience a boost, considering the huge reservoir lake.

The total cost of the project has been estimated at 25 billion $, for which 60% can be attributed to the construction works, and 40% to resettlement. In June 2003, the first 2 generating sets have started operation, and through gradual expansion, the total facility will be fully operational in 2009.