Dams - pros and cons

All energy technologies have major advantages and disadvantages, and hydropower is no exception. In this briefing paper, Juergen Giesecke from Energie-Fakten presents a comprehensive overview of pros and cons, and a message that dams can make a major contribution to mankind's energy (and food) supply, provided that we exploit the pros while mitigating and managing the cons.

Mankind has been managing water flows for four millennia in order to provide for the necessities of life. The practice of storing large water quantities using dams started with ancient Mediterranean cultures, and has been continuously developed up until modern times. The world has about 46,000 dams that are higher than 15 meters (earthfill and masonry). There were 6 billion people on the planet in 2002 – a number increasing by 80 million each year – and 20% of them suffer from water scarcity while about a third lack basic sanitary facilities.

Well over 70% of large dams around the world are used for the irrigation of agricultural land to secure food supply. Further important functions are the supply of drinking water for citizens, processing water for industry and commerce, and cooling water for thermal power stations. A further function is flow control for flood protection and electricity generation from hydropower, the most effective use of this constantly regenerating energy.

By holding water in reservoirs and releasing it as the need arises, dams modify the existing natural conditions of life for animals and plants as well as the habitat of local population, primarily through the relocation of people who must leave the area where they settled, live and cultivate land. Roads change, and religious and cultural sites are disturbed for the future reservoir. Accumulation of nutritient-rich sediments not only leads to silting of the reservoir, but it also deprives the river downstream of natural sedimentation and manuring, and it disturbs its seasonal flow where areas are intermittently flooded and drained. In addition, depending on the characteristics of subsoil and soil layers, groundwater levels may change. Changes in the micro-climate near artificial large reservoirs can be significant in tropical climates, through increased water evaporation, and the slack water near dams facilitates development of life-threatening diseases. Also, we cannot ignore security risks resulting from the storage of large quantities of water, or possible collapse of the barrage construction.

Dams have, depending on type and provisions, demonstrated lifetimes of well over 100 years. They make a significant contribution to the basic necessities of life for the resident population and they have become an essential part of the human imprint on the cultivated landscape. However, they require careful precautions and provisions to minimise ecological damages, impact on landscape aesthetics and influence on the lives of people, animals and plants, and to keep risks small.

For this purpose, over the last three decades and on a global scale, professional societies have developed comprehensive instructions, manuals, regulations and training/education programmes.

Interdisciplinary cooperation of specialists from engineering, natural sciences, economics and humanities have now become as self-evident for large dam projects, especially those with considerable use of hydro power, as have public relations and awareness raising with the broad population.