The benefit of large hydroelectricity dams has long been a topic of great controversy. It was brought back to my attention today with the Three Gorges Dam in China ‘Facing its biggest challenge yet’. Heavy flooding in Sichuan province has seen 146 lives lost with 40 more people missing. 1000 farmers have also been evacuated, the China Daily reports.

The World Commission on Dams spent 2 years researching the effectiveness of large scale dams like the Three Gorges Dam, so are they really worth it?

In relation to large dams the commission found that:

• Large dams have demonstrated a marked tendency towards schedule delays and significant cost overruns.

• Large dams designed to deliver irrigation services have typically fallen short of physical targets, did not recover their costs and have been less profitable in economic terms than expected.

• Large hydropower dams tend to perform closer to, but still below, targets for power generation, generally meet their financial targets but demonstrate variable economic performance relative to targets, with a number of notable under- and over-performers.

• Large dams generally have a range of extensive impacts on rivers, watersheds and aquatic ecosystems – these impacts are more negative than positive and, in many cases, have led to irreversible loss of species and ecosystems.

• Efforts to date to counter the ecosystem impacts of large dams have met with limited success owing to the lack of attention to anticipating and avoiding impacts, the poor quality and uncertainty of predictions, the difficulty of coping with all impacts, and the only partial implementation and success of mitigation measures.

• Pervasive and systematic failure to assess the range of potential negative impacts and implement adequate mitigation, resettlement and development programmes for the displaced, and the failure to account for the consequences of large dams for downstream livelihoods have led to the impoverishment and suffering of millions, giving rise to growing opposition to dams by affected communities worldwide.

• Large dams display a high degree of variability in delivering predicted water and electricity services – and related social benefits – with a considerable portion falling short of physical and economic targets, while others continue generating benefits after 30 to 40 years.

• Since the environmental and social costs of large dams have been poorly accounted for in economic terms, the true profitability of these schemes remains elusive.

It seems, from this research, that large scale dams are not worth it. Which leaves the question, why are they built? The Commission’s report addresses this question highlighting:

At the heart of the dams debate are issues of equality, governance, justice and power – issues that underlie the many intractable problems faced by humanity

Let’s not also forget about our endless thirst for energy, I write this from an air-conditioned cafe in the French concession of Shanghai. How much of my comfort is being fuelled by the Three Gorges Dam? Probably none, but how would I know?

To dam or not to dam, should they still be built? What do you think?