David Le Page
A dramatic report from the World Commission on Dams (WCD), based in Cape Town, has overturned the long-standing assumption that hydroelectric power is environmentally clean.
According to the report, dams often release large quantities of methane gas from rotting vegetable matter. Methane is a 20 times more effective greenhouse gas than carbon dioxide – the major gas emitted by coal-fired power stations.
The news promises to complicate many existing assumptions about the place of hydroelectric power in long-term global energy planning. The unwanted methane is not created so much by vegetation submerged when dams are created, as by vegetation washed downstream into the reservoir throughout the life of the dam. Clearing vegetation before flooding can help, but the clearing method is crucial. The amount of methane later generated will vary according to dam depth, surface area, climate zone, altitude, temperature and surrounding vegetation.
According to the WCD, “a hydro-dam is [currently] seen as an environmentally clean technology”. This is certainly true of public perceptions, though many environmental organisations and NGOs would, it seems, beg to differ on the basis of the permanent social and environmental disruptions caused by big dams.
Dams have long been seen as clean energy sources, vital since the ratification by most countries of the 1997 Kyoto Protocol Agreement on Global Climate Change. Under the agreement, polluting countries will be able to trade carbon emissions with each other. Countries producing less than their quota of emissions will be able to sell pollution credits to countries over quota.
In the report 20 scientists from Brazil, Canada, Finland, the United States and France concluded that all 30 dams studied emit carbon dioxide and methane. In northern climes, hydropower appears to be a 10th as polluting as, say, the equivalent coal power station.
But in tropical climates it can be worse. Five of 10 Brazilian dams appear to produce as least as much, if not more greenhouse gas, than equivalent power stations.
However, the study considered only 30 dams. A lot more research is required before the full effect of hydropower on global warming can be properly assessed. The basic point is dams just aren’t automatically as innocuous as they look.
“The discovery that a dam reservoir emits greenhouse gas emissions is, by itself, inconclusive,” said Jamie Skinner, a WCD senior adviser quoted in its methane report. “Even cows produce methane, but so do the deer and rotting grass in a meadow before cows were introduced.”
Similarly, natural lakes also produce methane emissions. The effect on South Africa, for the meantime, is likely to be limited, as hydropower currently contributes only 2% of Eskom’s total power needs, according to the energy company’s Vanida Govender.
As a developing nation, South Africa doesn’t yet have greenhouse gas reduction targets under the Kyoto Protocol, despite being one of the world’s top 15 polluters, according to Earthlife Africa’s Richard Sherman.
Moreover, given the South African climate, it’s highly unlikely that any South African dams used for hydropower are more polluting than their thermal equivalents.
Until recently any such emissions might have been the responsibility of Eskom. But since the government passed reformed water laws a couple of years ago that effectively nationalised all water resources, the state will have to bear the cost of dealing with greenhouse emissions from South African dams, should that ever become necessary. At present Eskom’s capacity is about 40E000MW, with about 4E000MW of that surplus capacity. According to Govender, new capacity is expected to be required only around 2008 or 2010.
But the dam issue will continue to affect us. As South Africa is only 75% electrified, and demand is growing at an average 2,8% a year, Eskom will be looking north to the Southern African Development Community countries to satisfy its electrical needs.
There is little room for further development of hydropower in South Africa itself (a potential total of 7E500MW), but there are considerable possibilities in countries like the Democratic Republic of Congo. The total potential for Southern Africa is 142E000MW. Building dams in these countries will most likely raise substantial concerns about methane emissions, quite apart from the other environmental and social concerns, which Sherman considers are regularly underplayed. He argues that small 10MW hydropower schemes should be considered in preference to large hydropower schemes and thermal power stations.
But it will take a long time for such schemes to make a dent in South Africa’s yearly contribution to global warming, which includes at least 690E000 tons of carbon dioxide.