Hydropower - glass half full or half empty?

Michelle Parkes · 9 June 2022

Electricity generated through flowing water. What’s not to like? It’s renewable, it’s clean. Surely there’s nothing controversial to see here? However, like all energy resources, hydropower has its pros and cons.

In its most simple terms, hydroelectric power is generated using flowing water to spin a turbine which is connected to an electric generator. In some cases small scale hydroelectric schemes have been implemented but the amount of energy generated is quite small and wouldn’t quite power a home for a year.

For large scale electricity you require a hydroelectric dam. These allow water to be directed downward through the turbine for maximum energy production. As an example, the Hoover Dam in America provides power to more than 1.3 million households across Nevada, Arizona and California.

Unlike sun and wind power which can’t provide consistent energy supplies, water flows 24/7. Similar to other renewable sources, the energy produced by hydroelectric plants isn’t toxic or adding to the greenhouse gases polluting our atmosphere. Its flexibility is highly attractive as not only can it reach maximum capacity in under 2 minutes but it can be stopped just as quickly.

Sounds great! And in some cases it can be. However, there are a number of environmental issues around hydropower worth noting. You need a lot of water for a plant to be effective, this means damming and diverting waterways. As you can imagine that has a negative impact on native aquatic ecosystems. The reservoirs at the tops of the dams are often stagnant. As the vegetation at the bottom of the dam rots, it will release extra carbon into the atmosphere. Harmful algae also becomes more abundant which is toxic to marine life.

Fish often need to migrate to reproduce, dams obstruct their routes and can be highly detrimental to fish populations.

Hydropower is particularly popular in the Amazon as it’s plentiful and also much cheaper than other sources of energy. Over 150 dams have been built and more are proposed. These have led to the displacement of many indigenous tribes such as the Asháninka - their livelihood depends on the rivers. Roads are constructed to build the dams which leads to deforestation. More forest edges dry out the understory of the rainforest and makes the forest more susceptible to fires. Ironically this reduces the rainfall needed to operate the hydroelectric plant.

Scientists have agreed that dams can even trigger earthquakes. They add weight to the Earth’s crust and it’s believed that at least 100 earthquakes have been induced by dams.

It’s not all doom and gloom though. Bhutan is the only carbon-negative country in the world. A lot of this is owed to their tree planting initiatives. However they also rely heavily on hydropower. They stay away from big dams, and instead have run-of-the-river schemes. This means that water flows through them rather than being stored behind them. They are vulnerable to climate change though. If the rivers become too low, they can only provide a fraction of their full capacity.

Whenever it comes to a conversation about green energy, a mixture of solutions seems to be the most viable. Hydropower used in combination with more weather dependent renewables, such as solar and wind, is ideal.