The world’s last free-flowing rivers are under threat. What is commonly thought of as a green solution to the energy crisis is destroying the planet’s last remaining pockets of untouched wilderness and intact ecosystems. Today, there are roughly 60,000 large dams around the world. Three thousand seven hundred more are currently planned or under construction. Over 500 of them are going to be in-built protected areas.

At first sight, the concept of hydropower may be a simple one. Flowing water is trapped ahead of dams, then directed through turbines, which spin to create electricity. It may seem to be a green solution to meeting the world’s growing electricity demand, but it is immoral. Dams emit greenhouse gases, endanger fish species, and might uproot communities. So, all this leads us to the question: What is the real cost of hydropower?

The environmental effects of hydropower

To understand hydropower’s environmental impact, we first must understand the value and characteristics of a free-flowing river. In a wild river, animals, like migratory fish, can swim up and downstream at will. Groundwater and aquifers naturally refresh the water, silt, and other natural materials can move along freely. The water moves out onto the floodplain calmly with the seasons, delivering essential nutrients to wildlife and other habitats, signaling fish to spawn, and bringing nutrients back to the river itself. The sad news is that not many wild rivers are left; two-thirds of them are already dammed, which is increasing daily.

What started with old fashioned waterwheels has developed into modern hydroelectric plants embedded in dams to create power. Currently, 22% of the world’s electricity is provided by renewable resources, 73% of which is hydropower. Although hydropower is renewable, it is not green. Building a vast barrier like a dam destroys the river’s single most vital thing: its flow. Both the reduced downstream flow and the reservoir upstream can destroy wildlife habitats and farmland, either through drying or flooding.

A dam also changes the structure of a river. It slows the water flow, implying that sediments like sand or gravel hit the dam and therefore drop to the riverbed. In a way, dams are creating giant underwater sandboxes, and these are bad news for fish, which rely on clean, rocky bottoms.

The clustered sediments are not suitable for the dam itself either, because as the area ahead of it is filled up with more and more sediment, it holds less and less water. Dams do not just form a barrier for sediment but also mean a drastic impact on flora and fauna. When the flow of a river is blocked, fish cannot reach their spawning grounds, and over time, dammed rivers can cause drastically reduced fish populations.

Currently, the most common way of solving this migration problem is installing fish ladders. Fish ladders are stepped pools that allow fish to swim or jump from one pool to another up and behind the dam. Most of the time, they do not work in real cases. The structures are often too high or too steep, too small to support massive migrations, or not sufficient to hold enough water. Even if fish ladders do succeed, they might work for fish like salmon, but not for every kind of fish because some, like eels, cannot jump.

Blocked migration routes are not the only problem. Reservoir water usually contains an excess of algae or other aquatic weeds, which may force out other animals and vegetation. The water in the reservoir is often also low in dissolved oxygen and colder than normal river water. When this water is released from time to time, it can have a foul impact on wildlife. As a result of all these negative consequences, worldwide freshwater species populations have already experienced a staggering 83% decline since 1970. More dams will likely further deplete their numbers.

Hydropower dams do emit greenhouse gases.

There is a popular consent that hydropower is a vital element for the energy industry’s shift away from fossils, but one fundamental piece of data is missing from the argument. It might sound counterintuitive initially, but hydropower is not emission-free. Around 10% of the world’s hydropower facilities emit as many greenhouse gases as conventional fossil-fueled power plants. Some existing dams within the lowland Amazon have even been shown to be up to 10 times more carbon-intensive than coal-fired power plants. Generating power by spinning turbines with water does not directly emit greenhouse gases. So, how are they getting created?

When reservoirs cover organic matter like dead plants, trees, fields, and farmland, they produce greenhouse gases, especially in warm climates. The organic material breaks down and releases gases like Carbon dioxide and methane into the reservoir water. Furthermore, these are the two major greenhouse gases related to global climate change. Worldwide, the rotting vegetation in reservoirs represents 1.3% of the overall annual global emissions caused by humans. These passive emissions can be alarming, but it also shows the potential to resolve these issues.

A possible solution to make dams nature friendly

Hydropower must be viewed as a part of a broader strategy for energy during which the prices and benefits of various sources should be assessed and weighed against one another. A strategic mixture of solar, wind, and storage technologies around river basins may well be an option. More significant investments have to be made in detailed upfront planning and environmental impact assessments, allotted by independent scientists.

Existing dams should be upgraded and retrofitted where possible rather than building new ones. Moreover, fish passage systems must be optimized to create it more friendly for all different fish varieties. In October 2020, several environmental groups and the industry that operates America’s hydroelectric dams announced an unusual agreement to work together to cut back the environmental harm caused by dams. They are also cooperating to get rid of older dams that are not any longer needed.

More than 1000 dams in the United States have already been torn down in recent decades. In many of these places, such as the Elwha River in Washington state, nature has come roaring back, with fish populations increasing. It is expected that, if the trend continues, between 4,000 and 36,000, more dams will be removed in the United States by 2050.

The world’s free-flowing rivers are crucial for the environment and humans alike. Furthermore, it is now more critical than ever to choose wisely whether we want to build new dams. It is about finding the right balance between hydropower and rivers and, more generally, between energy consumption and ecosystem conservation.

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