Your city or town probably either has a large, brand-new hydropower dam or you know of an old one, located on the outskirts; a crumbling relic from an earlier period in your state’s history. I know this because according to the national nonprofit conservation organization American Rivers, on average our country has constructed one dam every day since the signing of the Declaration of Independence. And the U.S. Army Corps of Engineers counts approximately 75,000 dams that are greater than six feet along the waterways of the United States. In addition, there are at least tens of thousands of smaller dams spanning our rivers and streams.
Whichever version of the structure is in your area, it seems that dams divide us. While some regard them as a clean energy source, others view them as a danger to river otters and fish populations.
So, are our dams good for the environment, or a threat to wildlife?
Dams: Renewable energy; clean air
Water flowing downstream creates kinetic energy. A hydroelectric power plant converts this energy into electricity by forcing water, often held at a dam, through a hydraulic turbine that is connected to a generator. The water then exits the turbine and is returned to a stream or riverbed below the dam.
Today in the U.S., it’s estimated that dams generate enough hydropower to supply electricity to 28 million households, the equivalent of about 500 million barrels of oil.
Those in favor of dams cite the facts that hydropower is renewable, climate-friendly and domestic. Dr. Glenn F. Cada, a researcher at the Oak Ridge National Laboratory – Environmental Sciences Division, confirmed in a 2007 article that conventional hydroelectric projects, with dams and reservoirs, are used all over the world to produce renewable energy. In the United States alone, conventional hydropower supplies 7 percent of the nation’s electricity. And in light of increasing concerns about fossil fuel emissions and biomass combustion on carbon dioxide levels in the atmosphere — causing global warming — the benefits of using hydropower are clear.
Dam proponents say that some species of wildlife benefit, too. In Wisconsin where I live, dams provide open water in winter where bald eagles can feed. In fact, several of my state’s towns hold eagle-watching festivals near the sites of their dams in winter where wildlife watchers come to spot the raptors.
Dams: Death of fish; source of floods
There are others, however, who would like to see all dams removed. They argue that the ability of conventional hydropower to meet our increasing energy demands is limited. By diverting rivers and streams from their natural courses for power, dams remove water needed for healthy ecosystems. Dams prevent the flow of plants and nutrients, make recreation such as canoeing, kayaking and fishing more difficult, and impede the migration of fish and other wildlife. Fish passage structures may enable a percentage of fish to pass around a dam, but multiple dams make safe travel difficult. And some dams built 50, 100 or even 150 years ago are no longer serving their intended purpose but are still standing, depriving communities of their natural flood protection, often making flooding worse upstream.
Dam opponents also point out that since dams withhold and then release water to generate power for peak demand periods, they cause downstream stretches to alternate between no water at all and powerful surges that erode soil and vegetation and flood or strand wildlife. These irregular releases destroy natural seasonal flow variations that trigger natural growth and reproduction cycles in many species, such as salmon. Salmon depend on steady flows to flush them downriver early in their life and guide them upstream years later to spawn. Stagnant reservoir pools disorient migrating fish and increase the duration of their migration.
Water temperatures are negatively affected, too. By slowing water flow, most dams increase water temperatures. Other dams decrease temperatures by releasing cooled water from the reservoir bottom. Fish and other species are sensitive to these temperature irregularities, which often destroy native populations.
Last year saw an unprecedented number of dam removal projects, on rivers including Maine’s Penobscot River, Washington’s Elwha and White Salmon Rivers, and Maryland’s Patapsco River. There is even a movement gaining ground to remove one of our most massive dams: the O’Shaughnessy, which created the Hetch Hetchy Reservoir in Yosemite National Park.
Do you think removing dams is needed to restore fish migration routes, renew river recreation, and protect communities downstream from floods? Or could restoring old dams and building new ones be a good alternative to fossil fuels?
Feature photo: In Wisconsin where I live, dams provide open water in winter where bald eagles feed. ©Bob Leggett
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