The world has had a century-long love affair with dams.

In the 1930s dam-building helped kick-start a depressed U.S. economy, whilst the Egyptian economy was transformed by the Aswan dam on the Nile. Dams could provide seemingly limitless and environmentally friendlier electricity than their nuclear and fossil fuel counterparts. Dams could ensure water for parched fields or thirsty cities. Dams could help control floods.

Now the love affair is over. The world's forty-five-thousand big dams have often generated as much controversy as they have benefits.

Think again

The environmental and social costs of big dams have at times proved unacceptably high. Fragile ecosystems have been damaged irreparably. Irrigated land has turned to salt. And millions have been forced to abandon their homes and their livelihoods.

It's all triggered a radical re-think which the Independent World Commission on Dams (WCD) was set up in 1997 to investigate.

Two-and-a-half years and ten million dollars later, the WCD has produced a four-hundred-and-fifty-page report which experts from all sides of the great dam debate were asked to contribute to.

The Commission evaluated a number of dams to determine their overall cost/benefit ratios. Had the environment suffered? Had local communities suffered? And if so, were those costs acceptable to the overall benefit experienced?

The dam debate

In a world of over 3 billion people, how do you provide adequate energy and water needs or continue to provide the insatiable energy demands of industrialised nations? Step up polluting nuclear and fossil fuel energy production? Or go for the socially damaging and 'not-as-clean-as-once-thought' hydro power? The problem for planners is that they're damned if they do and damned if they don't.

With this intractable problem in mind, the 12 independent commissioners set off to study seven big dam projects round the world.

The Tucurui Dam, Brazil

During the 1970s Brazil's planners dreamed of taming the Amazon's wild rivers to feed the demands of the country's power-hungry factories. Today, 95% of Brazil's electricity comes from hydroelectric sources.

Built in 1985, the Tucurui Dam is huge, generating all the electricity required by cities and industries across northern Brazil. But progress came at a great price.

Forty-thousand people displaced upstream by rising waters weren't happy with their resettlement. Fifteen years after the dam was built, relocated families are still fighting for compensation and Union leaders working on their behalf say many of their members have fallen victim to physical intimidation by the power company behind the dam.

Another objection to the scheme was that local inhabitants were not benefiting from the cheap energy produced by the scheme - with more than half the power generated going directly to industrial complexes nearby.

Now Phase II, which will add 11 new generators to the dam, is underway and Union leaders fear more land and people will be affected.

Elsewhere, dams have been less socially and environmentally damaging. Norway, where Hydro schemes generate 99.6% of the country's power, seems to have got it right. How?

Norway

Norwegians consume more energy per capita than any other country on earth, about ten times the world average. Power is cheap thanks to numerous hydro-electric power projects. But even here they're now questioning whether big dams are really the answer.

From the beginning, Noway's tough rules for Hydro schemes have minimised the social and environmental costs and, luckily for Norway, their mountainous geography means that most hydro plants are located in remote high locations which remove the need to drown vast tracts of low-lying land.

Norway's success so far, it seems, has certainly been helped by its natural topography but it's democratic and transparent decision-making process meant that here, dams worked.

But Norway is facing an uncertain future. Nearly all the areas that could support Hydro schemes without affecting the local population have been exploited. Now, this power-hungry nation has a problem. Hydroelectric power has given Norwegians cheap energy which has led to excessive use and spiraling demand. What will the Norwegians do next?

Listen and learn:

It seems clear that while dams are not the panacea for the world's energy and water problems, they could provide a valuable source of 'cleaner' energy but only if governments and power companies are prepared to listen to the people.

Where Hydro schemes have worked, there has been a great emphasis on public participation and environmentally-sensitive construction.

The report also notes that the thrust of recent protests against globalisation is the rising anger over lack of openness in global decision-making. And it's exactly the same issues - of transparency and accountability - which surround the Great Dam Debate.

Every time a wall is built across a river, these issues must be addressed. Take heed the report warns, or be dammed.