Is Hydropower Good Or Bad For The Environment?

Hydropower has long been touted as a clean and renewable energy source, but in recent years its environmental impact has come under greater scrutiny. With many countries seeking to reduce their carbon emissions, there is intense debate around whether hydropower’s pros outweigh its cons.

Hydropower generates electricity by using turbines to convert the energy from flowing water – usually dams – into mechanical power. This accounts for over 16% of the world’s electricity production, making it an important part of many nations’ energy strategies.

However, hydropower facilities can significantly disrupt local ecosystems and communities. Large dams flood habitats, alter water levels, and hamper fish migration patterns. While hydropower may provide clean electricity, its overall environmental footprint may be far more damaging.

This article will examine the key pros and cons of hydropower, evaluating whether on balance it is beneficial or harmful for the environment. With nuanced analysis of factors like emissions, wildlife impacts, and sustainability, a qualified verdict can be reached on this complex issue.

Pros of Hydropower

Hydropower is considered a renewable energy source because it relies on the water cycle to generate electricity. The water cycle is continuously replenished by the sun, making hydropower an indefinite energy supply.

Hydropower can reduce dependence on fossil fuels like coal, oil, and natural gas. According to the U.S. Department of Energy, hydropower accounted for over 6% of total U.S. electricity generation and 43% of electricity generation from renewables in 2019 (Source). Using hydropower to generate electricity can help limit greenhouse gas emissions.

Hydropower has relatively low operating costs compared to fossil fuel plants because the “fuel” (flowing water) is free. This makes the cost of generating electricity at hydropower facilities very predictable.

Hydropower can provide reliable baseload power that is available on-demand. The flow of water in rivers and over dams can be controlled, allowing hydropower to provide continuous electricity generation.

Cons of Hydropower

While hydropower is a renewable source of energy, it does have some negative environmental impacts. Here are some of the main cons of using hydropower:

Hydropower dams disrupt river ecosystems. According to the USGS, “Dams change the environment and can affect land use, homes, and natural resources” (https://www.usgs.gov/special-topics/water-science-school/science/hydroelectric-power-water-use). Dams prevent fish migration and impact spawning, which affects the biodiversity of river habitats.

Reservoirs created by hydropower dams contribute to greenhouse gas emissions, especially methane. As plant matter decays in reservoirs, methane is released. Per the Climate MIT article, “Methane is a greenhouse gas 25 times more potent than carbon dioxide” (https://climate.mit.edu/ask-mit.edu/why-arent-we-looking-more-hydropower).

Silt build up behind dams reduces storage capacity over time. Silt alters the river habitat downstream as well. Turbines can also get damaged from silt build up.

Flooding land to create reservoirs negatively impacts wildlife habitats. The EIA reports that turbines injure and kill migrating fish (https://www.eia.gov/energyexplained/hydropower/hydropower-and-the-environment.php). Changing water levels in reservoirs impact shoreline habitat too.

Impact on Wildlife

The construction of dams for hydroelectric power has devastating effects on wildlife habitats and populations. According to The Hill’s article, “Hydropower is hurting wildlife”, damming rivers floods forests, wetlands, and other ecosystems that many species depend on. This can wipe out entire habitats and food sources for wildlife.

Dams also act as a barrier for migratory fish like salmon that must travel upriver to spawn. As the UCSUSA report “Environmental Impacts of Hydroelectric Power” explains, fish ladders and elevators meant to assist migration are often inefficient, blocking access to critical upstream habitat. This can decimate fish populations.

In addition, fluctuating water levels from dam releases and drainage can leave shorelines and riverbeds exposed. This disrupts feeding, nesting, and other wildlife behaviors attuned to seasonal river flows. Hydroelectric facilities often fail to recreate the natural flow variability that ecosystems and species depend upon.

Impact on River Ecosystems

The construction of hydropower dams can significantly alter river flow, nutrients, and habitats, with negative impacts on ecosystems (https://www.eia.gov/energyexplained/hydropower/hydropower-and-the-environment.php). Dams often regulate river flow by storing water in reservoirs and releasing it through the turbines to generate electricity during peak demand periods. This can drastically change the natural seasonal flow patterns of a river, as well as decrease overall flow downstream from the dam.

The alteration of river flow impacts the movement of nutrients and sediment in the river. Slow moving reservoirs behind dams act as traps for sediment and nutrients, preventing their downstream transport. The reduction in nutrient transport negatively affects floodplain vegetation that depends on annual inputs of nutrients and minerals from sediment deposits left by flood waters (https://hydroreform.org/about-hydropower/hydropowers-impact-on-rivers/). Overall, dams disrupt the connectivity between rivers and their floodplains, reducing productivity.

Greenhouse Gas Emissions

While hydropower is considered a renewable energy source, hydroelectric dams do contribute some greenhouse gas emissions. The flooding of land to create reservoirs leads to decaying vegetation and organic matter, which releases methane into the atmosphere. Methane is a powerful greenhouse gas with a global warming potential much higher than carbon dioxide.

According to research from the U.S. Department of Energy, reservoirs in temperate regions may emit over 100 g CO2-eq/kWh, though global estimates put the median around 24 g CO2-eq/kWh. While higher than wind or solar power, this remains far below emissions from burning fossil fuels like coal and gas. The IPCC estimates electricity from coal produces 820 g CO2-eq/kWh, and gas produces 490 g CO2-eq/kWh. So in terms of climate impact, hydropower is preferable to fossil fuels.

Strategies like clearing vegetation before flooding and maintaining oxygen levels in reservoirs can help mitigate methane emissions. Overall, hydropower still plays an important role in transitioning to renewable energy while efforts continue to further reduce its footprint.

Mitigation Strategies

There are several strategies that can help mitigate some of the potential negative environmental impacts of hydropower projects:

Advanced turbines can be installed that allow for safer fish passage. Traditional turbines pose a threat to migratory fish, but advanced turbine designs like minimum gap runners and fish-friendly blades can greatly reduce fish injury and mortality rates.

Monitoring silt buildup levels behind dams is important. Too much siltation can negatively impact spawning habitat and release methane emissions. Strategies like flushing sediments through the dam and dredging can help manage silt accumulation.

Methane emissions from reservoirs can be mitigated through methane capture systems. These systems essentially put a cap over the reservoir to trap greenhouse gases which can then be flared or used for energy production, reducing overall emissions.

Case Studies

Several case studies showcase the real-world benefits and challenges of hydropower projects around the world:

In Norway, the Tafjord hydropower project illustrates the environmental benefits of this renewable energy. Built in the late 1950s, this project provides 100% renewable power to over 170,000 households, avoids 460,000 tonnes of CO2 emissions per year, and enables aluminum production with low carbon footprint. However, the original construction did significantly alter the lake ecosystem. To mitigate impacts, the project now includes modern fish ladders and breeding programs for endangered fish species (https://www.gilkes.com/case-studies/tafjord-balancing-reservoir-norway/).

China’s Three Gorges Dam, the world’s largest hydropower project, provides 22,500 MW of renewable power displacing over 100 million tonnes of CO2 annually. However, the massive reservoir flooded cities, displaced over 1 million people, and altered downstream river hydrology. Efforts are underway to restore fish populations and protect endangered species like the Yangtze River dolphin (https://documents1.worldbank.org/curated/en/247261519658051630/pdf/Better-hydro-compendium-of-case-studies-2017-better-understanding-better-examples-better-policies.pdf).

Brazil’s Itaipu hydroelectric project supplies 17% of the country’s electricity with minimal emissions. However, the large reservoir flooded 1,350 sq km of land. Mitigation efforts included relocating and compensating affected communities as well as programs to monitor water quality and reforest flooded areas (https://www.hydroreview.com/hydro-industry-news/rehab-reports-case-studies-of-major-hydro-rehabilitation-worldwide/).

The Future of Hydropower

As global energy demand continues to grow, hydropower will play an increasingly important role in meeting electricity needs. According to the International Energy Agency, hydropower will remain the largest source of renewable electricity in the world through 2023 and beyond (https://www.iea.org/energy-system/renewables/hydroelectricity).

Advancements in hydropower technology, such as more efficient turbine designs, remote monitoring capabilities, and pumped storage, will enable more flexibility and improve the overall performance of hydropower plants. Compared to other renewable energy sources like solar and wind power, hydropower can provide consistent baseload power since output is not intermittent. With the development of new pumped storage hydropower projects, excess electricity generated from other renewables can also be stored for later use.

While the potential for new large-scale hydropower dams is limited in many parts of the world, adding generating capacity to existing dams and canals, as well as developing small hydropower projects, provide opportunities for further growth. The U.S. Department of Energy has identified hydropower as key to building a clean energy future because of its renewable, flexible, and reliable attributes (https://www.energy.gov/eere/water/articles/hydropower-key-clean-energy-future-heres-why).

Conclusion

In summary, hydropower offers several pros, such as being a renewable and reliable energy source that produces no direct waste or emissions. However, it also has major cons, including the flooding of large areas of land, disruption of river ecosystems and wildlife habitats, and potential methane emissions from reservoirs.

On balance, while hydropower can play a role in the renewable energy mix, the environmental impacts make it difficult to claim it is truly a “clean” energy source. The flooding and disruption of river systems can cause irreparable damage. However, with proper mitigation strategies, site selection, and operating procedures, some of the negative effects can be reduced. Overall, hydropower’s benefits must be carefully weighed against its significant downsides on a case-by-case basis. But alternatives like solar, wind and geothermal should likely take priority over building new large dam projects when considering options for environmentally sustainable renewable energy.