Environmental impacts
of hydropower

Environmental impacts of hydropower

The devastating impacts of climate change on the environment are numerous, and it is our responsibility to protect and preserve the world around us. Part of that responsibility is to look at ways to reduce the impact of our energy supply and the ways we generate electricity.

In the Northwest, decarbonizing the grid has become a high priority. Oregon and Washington have both set a number of ambitious goals to achieve a 100% carbon-free energy supply.

In the interest of the environment, it’s also necessary to look critically at the impact of energy sources we consider clean and renewable. These terms describe energy sources that include hydro, wind, and solar, and are attributed to them as a result of not emitting greenhouse gasses. That does not mean, however, that they have no impact whatsoever.

Downsides of dams

The truth is that all energy sources change and influence the environment to some degree. Hydropower is no exception.

In general, the most straightforward impact of a dam is that it changes the natural flow of a river. Behind the dam, wetlands, creeks, and rivers can become impounded, significantly altering the habitat. Downstream, changes the flow of water can impact water quality and the distribution of sediment. In some cases, dams significantly reduce water flows and dry up habitat areas.

Hydroelectric dams can also block off the natural migration of native fish, while providing favorable conditions to invasive species that are better adapted to lakes than rivers.

To some extent, these impacts are also true of Northwest hydropower. Our dams in particular created challenges for fish like salmon and steelhead that migrate upriver to spawn. Additionally, juveniles travelling downstream must also navigate these facilities. As well, dams, in combination with other human-related activities, resulted in habitat loss for salmon and steelhead throughout the Columbia River basin.

Fish-friendly hydropower

However, the Northwest’s hydroelectric dams have undergone significant changes since they were first built to mitigate for these environmental impacts. Today, they lead the way in being fish-friendly and having a lowered impact while still producing clean, carbon-free energy.

In fact, data shows that fish survival past modernized dams can be as good or better than naturally flowing rivers. Technological improvements at dams, including scientifically engineered fish ladders and surface passage systems—like removable spillway weirs—help fish safely navigate the dams. Research by NOAA Fisheries shows that with the improvements that have been made, the survival of juvenile fish past the eight dams on the lower Columbia and lower Snake rivers is better now than when the Snake River was free flowing.

The combination of these fish ladders and weirs, along with new fish-friendly turbines and grates, all contribute to excellent fish passage at all eight lower Columbia and lower Snake dams.

Through the funding provided by hydropower, significant habitat restoration projects have been undertaken as well. The Bonneville Power Administration, who markets and sells the hydroelectricity generated at federally operated dams in the Northwest, has contributed billions to fish and wildlife activities.

These activities extend to hatchery programs that take place near many hydropower projects to bolster salmon and steelhead populations.

Effects on river temperatures

There is some concern as well that the slower flow of the river caused by dams has allowed dangerous temperatures to occur. When water temperatures surpass 68 degrees Fahrenheit, salmon and steelhead can be gravely harmed.

In truth, hydropower may be having the opposite effect. As atmospheric temperatures continue to trend upward in the Northwest, historical data shows that average river temperatures have remained consistent. The reason being is that the reservoirs behind dams increase the total volume of water, which is more insulated against extreme temperatures. This is similar to trying to boil a small pot of water as opposed to a large one.

What we do see is that this insulating effect causes the river temperatures to rise more slowly but stay warmer longer into the year. In undammed rivers along the West Coast, extreme temperatures and low waters can lead to dangerous temperature spikes that are much rarer in the Columbia and Snake.

This is not to say that salmon and steelhead are not still struggling today, but their greatest threat is now climate change and its impact on the ocean. In this way, our fish-friendly hydropower and its critical role in fighting climate change could in fact be an important tool in the recovery of these iconic species.

Methane emissions

Another concern is that hydropower can emit methane, a significant greenhouse gas, through its reservoirs. The accumulation of organic matter–either from submerging existing vegetation or by creating ideal conditions for aquatic plants–can break down and create anaerobic conditions. This process produces methane as a byproduct and releases it into the atmosphere.

This has certainly been true of dams closer to the equator and in more tropical climates. The Northwest, with its more moderate climate, does not experience these same issues. This is also a result of the location of our hydropower facilities, which have been constructed East of the Cascades in the dry, arid high desert.

Finally, the dams on the lower Columbia and lower Snake are run-of-the-river. This means that their reservoirs maintain a consistent flow and do not allow for these conditions to take place.

A study by the US Army Corps of Engineers showed that Northwest dams and their reservoirs do not create significant methane emissions.

Hydro is here to stay

Not all impacts are negative, either. Dams can control the amount and flow of water in the river and help reduce the effects of drought, flooding, and soil erosion. This consistency can be very beneficial to the river habitat and the species who call it home. And, much like the salmon and steelhead, the climate change fighting capabilities of hydropower provides many benefits to the Northwest’s ecosystem.

Northwest hydropower can provide renewable and reliable sources of electricity, but like all energy sources, there are impacts on the environment to consider. Our hydropower facilities have been in place for decades–some close to a century–and have seen significant upgrades and improvements over time. In that time, we have learned to mitigate for these impacts and find ways to reduce them while continuing to enjoy the numerous benefits our dams provide. As we look to the future, it is important that we remain vigilant in assessing and monitoring these impacts and finding solutions to make further improvements.

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