Small hydro could add up to big damage

A belief that 'small' hydropower systems are a source of clean energy with little or no environmental problems is driving the growing interest in mini, micro, and pico hydro systems that generate from less than 5 kilowatts up to 10 megawatts of energy.

Hydropower appears to be the cleanest and most versatile of renewable energy sources. But experience shows that optimism about its potential can be misplaced.

Hydropower uses water and gravity (a totally carbon-free and inexhaustible resource) to drive turbines and generate electricity.

Unlike fossil-fuelled power plants, hydropower plants produce no gases or fly ash emissions (fine particles generated by burning coal). And, unlike nuclear power plants, there is no radioactive waste to contend with. Nor is any resource consumed, because water is neither lost nor polluted. Reservoirs can also enhance the scenery, attracting picnickers and tourists.

As soon as the world took note of these virtues in the 1950s, hydropower became popular. Developing countries including Brazil, China, India, Malaysia, Thailand, and Turkey built increasingly larger dams, generating anywhere from a few hundred megawatts to more than 10 gigawatts.

Lessons of large hydro

Egypt's High Aswan Dam has become an iconic symbol of these projects - and their environmental impacts.

Projects like these fundamentally altered river ecosystems, often fragmenting channels and changing river flows. Natural lakes take hundreds of years to evolve from oligotrophic (low in nutrients) to eutrophic (rich in nutrients) status. But man-made reservoirs underwent this transition within a few years, degrading water quality, harming fisheries, bringing siltation and invasion by weeds, and creating environments suitable for mosquitoes and other disease vectors.

And where reservoirs displaced people or suddenly changed resource availability or agricultural capacity, they brought major socio-economic problems.

It was during the mid-1970s, some 20 years after a number of major hydropower projects had been commissioned, that reports of their adverse environmental impacts began to emerge.

By the end of 1970s it had become clear that the very optimistic, almost reverential, attitude towards hydropower projects that had prevailed during the early 1950s was misplaced. These projects damaged the environment as seriously as did fossil-fuelled power projects.

The mistake had been to see only the virtues, and to not prepare for possible problems, some of which surfaced only once a large number of projects had been commissioned at different locations.

The big question is: are we set to repeat the same mistake with 'small' hydro?

No evidence

Nearly everyone seems to believe that small hydro is a safe substitute for large hydro. Some assert it is entirely benign; others acknowledge some problems similar to the ones associated with large hydropower, but say these are too small to be of concern.

In a report on the environmental implications of renewable energy sources, the International Energy Agency notes: "Small-scale hydro schemes tend to have a relatively modest and localized impact on the environment. These arise mainly from construction activities and from changes in water quality and flow on ecosystems (aquatic ecosystems and fisheries) and on water use".

After the reassuring first sentence, the IEA goes on to list a number of environmental impacts and concludes: "The impacts of small-scale hydro schemes are likely to be small and localized, providing best practice and effective site planning are used."

But the fact is, it gives no evidence whatsoever to support the conclusion that the impacts will be "small and localized".

So far, the world has not experienced any major problems from 'small' hydro simply because the world has used 'small' hydro very sparingly.