Environmental Engineering Reference
In-Depth Information
Dams and hydropower
The traditional and very effective method of generating hydropower
has been to construct a dam across a river, let the mass and the level of
the water build up behind the dam, and then let the water fall at speed
into turbines at the bottom of the dam. So successful has this been that
this kind of hydropower generates no less than sixteen percent of the
world's electricity - far more than any newer source of renewable energy.
Hydropower has none of the short-term variability affecting most other
renewable energy sources - though of course it is vulnerable to drought.
But dams - big dams, at least - have fallen out of fashion. Anti-dam
campaigners, ranging from the US-based International Rivers Network to
the award-winning Indian novelist Arundhati Roy, have highlighted the
problems of dams in terms of population displacement, loss of river spe-
cies and even increases in greenhouse gases in tropical countries. In hot
climates the rotting vegetation which can build up around dams produces
a lot of methane and carbon dioxide. Partly as a result of NGO pressure, a
World Commission on Dams was set up in 1997, and in its widely praised
report of 2000, it acknowledged that “coercion and violence have been
used against communities affected by dams”, that dam projects had to
win “greater public acceptance” and that dam-project assessments should
also consider other ways to provide the services of energy, flood control
and irrigation offered by dams. The World Bank is now much more cau-
tious about financing new dams in developing countries. In the US, for
environmental reasons, the rate of decommissioning existing dams now
exceeds the rate of commissioning new ones.
But the age of dams (or “dam-age”, as NGO critics call it), is certainly
not over. China has just built the Three Gorges Dam on the Yangtze river,
the building of which has required the displacement of more than one
million people. This is the world's largest dam in terms of generating
capacity (some 25,000 MW), relegating the Itaipu dam on the Brazil-
Paraguay border (which has a capacity of 14,000 MW) to second place.
Much less controversial are the “run-of-the-river” hydropower projects.
These do not involve any damming or creation of reservoirs - just some
walls or conduits to channel part of the river water into turbines. They are
usually small projects. But one such project under discussion in Africa
is enormous. The two Inga dams currently operate at a low-output level,
despite the fact that they are situated at a point where water flow is huge
and the level drops nearly one hundred metres on the Congo river in
central Africa. The plan is to rehabilitate them for the construction of
