Is Hydropower Environmentally Friendly?

Hydropower is a renewable energy source that generates electricity using moving water. Hydropower plants capture the energy of flowing water by funneling it through a turbine, which spins a generator to produce electricity. As one of the oldest and largest sources of renewable energy, hydropower provides over 7% of total electricity generation in the United States and over 16% worldwide. https://www.energy.gov/eere/water/hydropower-basics

However, there is an ongoing debate about whether hydropower should be considered a green and sustainable energy source. While hydropower itself produces no air pollution or carbon emissions, large hydropower dams and reservoirs can have significant environmental impacts. These impacts raise the question of whether hydropower is truly an environmentally-friendly renewable energy. This article will examine the benefits and concerns around hydropower to evaluate whether it deserves the label of green energy.

Benefits of Hydropower

Hydropower generates electricity without using fossil fuels, which means it avoids the harmful air pollutants and greenhouse gases that come from those energy sources like coal or natural gas. Compared to a coal or gas plant, hydropower emits much less carbon dioxide and nitrous oxide per unit of electricity generated. According to the U.S. Department of Energy, hydropower avoids nearly 200 million metric tons of carbon emissions each year in the United States alone.¹ This makes it a renewable and clean energy source that can help reduce reliance on fossil fuels.

Since hydropower relies on the water cycle driven by the sun, it is considered a renewable source of electricity. The supply of water to generate power is continuously replenished through precipitation and runoff. As long as there is sufficient water flow, hydropower stations can generate emission-free electricity year after year.

Concerns About Dams

While hydropower is a renewable source of energy, dams can have many negative environmental and social impacts. One major concern is the impact dams have on fish migration and survival. Dams act as physical barriers that block fish from reaching their native spawning grounds and disrupt migration patterns that are vital for reproduction (Environmental Impacts of Dams, International Rivers). This can decimate local fish populations over time. Dams also alter natural water flows in rivers. The pools created behind dams slow down river flows, which causes increased sedimentation that can harm fish habitat downstream (How Dams Damage Rivers, American Rivers). Additionally, the changes in water temperature and oxygen levels caused by dams can negatively impact aquatic ecosystems.

Dams constructed for hydropower generation also lead to the flooding of areas upstream, which can displace local communities and destroy natural habitats. The relocation of people and the loss of land affects social structures and livelihoods tied to the river and surrounding region. According to the EIA, most dams built in the U.S. were primarily for flood control, municipal water supply and irrigation rather than hydropower. However, the environmental and social disruption caused by large dams remains an important consideration today.

Methane Emissions

One of the biggest concerns surrounding hydropower is the methane emissions produced from reservoirs. When large areas of land are flooded to create reservoirs, it leads to decaying plant material underwater that releases methane, which is a potent greenhouse gas. Methane has a global warming potential 25 times greater than carbon dioxide over a 100-year period, and 80 times greater over 20 years.

Recent research indicates that reservoirs created for hydropower emit significant amounts of methane through diffusion at the water surface and degassing through the turbines and spillways. According to the U.S. Department of Energy, methane emissions from hydropower reservoirs account for approximately 1.3% of total anthropogenic greenhouse gas emissions in the United States. However, some scientists believe the percentage may be higher when factoring in methane bubbling up from sediments.

The main strategies to mitigate methane emissions include avoiding flooding large wooded areas during dam construction, removing vegetation in areas that will be flooded, and designing dams to minimize organic matter decomposition. While methane emissions are a valid concern, hydropower overall has much lower lifecycle emissions than fossil fuel alternatives.

Impact on Wildlife

The construction of dams for hydroelectric power generation can significantly disrupt habitats and breeding grounds for wildlife, especially aquatic species ¹. Dams fragment previously connected aquatic ecosystems, blocking fish migration routes and preventing access to essential spawning locations upstream ². This can decimate local fish populations that are unable to reach their native breeding grounds. Reservoirs created by dams also flood forests, wetlands, and other wildlife habitats, destroying resources and food sources animals rely on.

Aquatic species most impacted by dams include salmon, sturgeon, and river dolphins. Their breeding cycles and migration patterns become disrupted when dams impede their ability to swim upstream. The impact cascades down the food chain, affecting many species that depend on fish as a food source. While fish ladders and other passageways can mitigate some effects, many dams still significantly reduce fish populations.

Beyond fish and aquatic life, dams disrupt local ecosystems, altering water flows, temperatures, and sediment levels. This affects a wide range of species, from birds to mammals, that have adapted to natural river environments. Overall, the fragmentation of connected habitats poses a major threat to biodiversity and wildlife dependent on free-flowing river systems.

Upstream and Downstream Effects

Dams significantly alter the natural flow of rivers, which has major impacts both upstream and downstream. One of the most notable downstream effects is that dams disrupt natural flooding patterns that distribute nutrients and replenish wetlands (Collier, 1996).

Dams also trap sediment that would normally flow downstream, robbing areas below the dam of enriched silt deposits during seasonal floods. This can make downstream areas more prone to erosion and reduce soil fertility for agriculture (U.S. Geological Survey, 2019).

In addition, the still reservoirs created behind dams slow down the river’s velocity, allowing suspended particles to settle to the bottom rather than being swept downstream. This interrupts the continuous movement of sediment that most rivers rely on (American Rivers, 2022).

Overall, while dams provide benefits like hydropower, flood control and water storage, they significantly disrupt the natural pulse of river systems downstream. Mitigation measures may help reduce some impacts, but altered flooding and sediment flows fundamentally change river ecology and morphology.

Comparison to Other Renewables

When comparing hydropower to other renewable energy sources like solar, wind, and geothermal in terms of greenhouse gas emissions, land use, and sustainability, hydropower has some advantages and disadvantages.

According to the U.S. Department of Energy, the life cycle greenhouse gas emissions from hydropower are much lower than fossil fuels and comparable to other renewables. Hydropower emits between 15-60 times less greenhouse gases than natural gas power plants and has nearly zero emissions during operation (https://www.energy.gov/eere/water/tracking-carbon-footprint-hydropower).

However, hydropower projects can produce methane, a potent greenhouse gas, from the decomposition of vegetation in reservoirs. Proper site selection and reservoir management can help minimize methane emissions. Overall, hydropower has much lower lifecycle emissions than fossil fuels (https://www.hydropower.org/factsheets/greenhouse-gas-emissions).

In terms of land use, hydropower’s footprint is generally larger than other renewables because of the size of reservoirs needed. But the land can often serve multiple purposes like recreation and wildlife habitat. Wind and solar projects also require large amounts of land. One benefit of hydropower is its high energy density – it can generate a lot of electricity from a relatively small area (https://www.cnbc.com/2022/06/02/why-hydropower-is-the-worlds-most-overlooked-renewable.html).

When it comes to sustainability, all renewable sources have their advantages and disadvantages. Hydropower’s flexibility helps balance variable solar and wind power. But dams can impact fish migration and sediment flow in rivers. Overall, a diversified renewable energy mix delivers the most sustainability benefits.

Mitigation Strategies

There are various strategies used to mitigate the environmental impacts of hydropower dams. One common approach is the installation of fish ladders, which are structures that allow fish to safely migrate past dams to access upstream spawning areas. Fish ladders create a series of pools with small waterfalls between them, enabling fish to steadily swim upstream (Protection, Mitigation and Enhancement Strategies At Hydroelectric Projects – FWEE).

Sediment control is another important mitigation strategy. Dams disrupt the natural flow of sediment downstream, which can increase erosion and starve downstream habitats. Techniques like sediment bypassing and sediment sluicing can help maintain sediment transport and prevent excessive buildup behind dams (Environmental Mitigation Technology for Hydropower: Environmental Mitigation Technology for Hydropower Summit IV).

Reservoir management techniques can also minimize ecological impacts. Strategies include maintaining minimum flow requirements, limiting water level fluctuations, and timed water releases that mimic natural flow patterns. Managing reservoir levels and river flows helps sustain downstream ecosystems and fish populations (ENVIRONMENTAL MITIGATION MEASURES AND BENEFITS).

The Future of Hydropower

Hydropower will continue to play a major role in renewable energy in the future. According to the U.S. Department of Energy, hydropower is a “key component of a clean energy future” as it offers advantages like flexibility, storage capabilities, and grid reliability (https://www.energy.gov/eere/water/articles/hydropower-key-clean-energy-future-heres-why).

New hydropower projects are focusing on sustainability and minimizing environmental impacts. Strategies include using non-powered dams or conduits, adding power at existing dams, and low-impact designs like in-stream turbines. There is also increased research into ocean and tidal power as renewable hydropower options (https://www.ucsusa.org/resources/environmental-impacts-hydroelectric-power).

Upgrades to existing infrastructure like turbine upgrades, dam rehabilitation, and adding pumped storage capabilities can also increase efficiency and capacity. With proper mitigation strategies, hydropower can continue providing clean, renewable electricity to meet future energy demands.

Conclusion

Overall there are both advantages and disadvantages to using hydropower as an energy source. The benefits include its renewability, low carbon emissions, and ability to meet peak energy demands. However, building dams can negatively impact local wildlife and ecosystems. There are also concerns around methane emissions from reservoirs and downstream effects on water quality and supply.

Based on the evidence, hydropower does appear to be one of the more environmentally friendly energy options currently available at scale. The emissions are far lower than fossil fuel sources. And many of the environmental impacts can be mitigated through careful planning and management. Implementing solutions like fish ladders, sediment control, and minimum water flow requirements can help reduce the harm to wildlife and habitat.

While not perfect, hydropower is a cleaner alternative that will likely play an important role as countries transition to 100% renewable energy. With proper safeguards in place, it can be part of the sustainable path forward.