3.      IMPLICATIONS

3.1        Energy Efficiency Implications

Although hydroelectric schemes are often regarded as a 'proven' technology that is fully commercialised, developments continue on all design aspects, such as new materials, improved construction techniques, and better appropriate ancillary systems. The most modern plants have energy conversion efficiencies of up to 90% and older plants can easily be upgraded to take advantage of recent efficiency improvements.

However sources for hydroelectric sites are limited, because rivers have a maximum flow potential. Therefore there are not many possibilities for expansion. Upgrading equipment can increase the efficiency and the output of existing systems, but many factors have to be evaluated in order to be economically feasible. One of these is the environmental impact that a large hydro scheme can have on its surroundings.

3.2        Social Implications

Hydro schemes are often built in remote areas away from rural centres. They can be a valuable source of employment to that area during construction and operation, while on completion they can provide added benefits, as reservoirs have scenic and recreation value for campers, fishermen, and water sports enthusiasts. Dams add to domestic water supplies, control water quality, provide irrigation for agriculture, and avert flooding. They can improve downstream conditions by allowing mud and other debris to settle out.

The most obvious negative impact of hydroelectric dams is the flooding of vast areas of land, much of it previously forested or used for agriculture. The size of reservoirs created can be extremely large. The La Grande project in the James Bay region of Quebec has already submerged over 10,000 square kilometres of land; and if future plans are carried out, the eventual area of flooding in northern Quebec will be larger than the country of Switzerland.

Although large hydro schemes are considered a valuable domestic source, in several cases they have flooded the homelands of native peoples, whose way of life has then been destroyed. It is estimated that during the past 50 years between 30 and 60 million people have been displaced by hydro development. For example, the controversial Three Gorges project at Sanxia in China will cover 30,000 hectares of agricultural land and displace more than a million people, but when completed will have a capacity of 17,680 megawatts, the largest hydroelectric scheme in the world. Consequently most large hydro-electric schemes being planned today are coming up against a great deal of opposition from environmental groups and native people.

3.3        Environmental Implications

Hydroelectric power plants have many environmental impacts, some of which are just beginning to be understood. These impacts, however, must be weighed against the environmental impacts of alternative sources of electricity. Until recently there was an almost universal belief that hydropower was a clean and environmentally safe method of producing electricity. Hydroelectric power plants do not emit any of the standard atmospheric pollutants such as carbon dioxide or sulphur dioxide which are given off by power plants fuelled by fossils. In this respect, hydropower is better than burning coal, oil or natural gas to produce electricity, as it does not contribute to global warming or acid rain.

However some recent studies of large reservoirs have suggested that decaying vegetation, submerged by flooding, may give off quantities of greenhouse gases equivalent to those from other sources of electricity. If this turns out to be true, hydroelectric facilities such as the James Bay project in Quebec that flood large areas of land might be significant contributors to global warming. On the other hand run of the river hydro plants without dams and reservoirs would not be a source of these greenhouse gases.

Large dams and reservoirs can have impacts on watersheds and threaten rare ecosystems, as decomposition may have drastic effects on water chemistry in a reservoir. The production of CO₂, for example, removes dissolved oxygen from water and since reservoirs have little circulation, subsurface water is normally anoxic (without oxygen) and thus hostile to fish and other forms of life. Damming a river can alter the amount and quality of water in the river downstream of the dam. Silt, normally carried downstream to the lower reaches of a river, is trapped by a dam and deposited on the bed of the reservoir. This silt can slowly fill up a reservoir, decreasing the amount of water, which can be stored and used for electrical generation. The river downstream of the dam is also deprived of silt, - often rich in nutrients and minerals -, which fertilizes the river's flood plain during high water periods. So restricting sediments behind dams can have an effect on agriculture through eroding away useful land.

Bacteria present in decaying vegetation can change mercury and other toxic chemicals present in rocks underlying a reservoir into a form (e.g. methylmercury), which is soluble in water. The mercury accumulates in the bodies of fish and poses a health hazard to those, especially native populations, who depend on these fish for food. (Raphals, 1992 on James Bay Cree population) The water quality of many reservoirs also poses a health hazard due to new forms of bacteria, which grow in many of the hydro rivers. Therefore, run of the river type hydro plants generally have a smaller impact on the environment.