Environmental Impact of Hydroelectricity

Hydroelectric power is considered to be a clean, renewable source of electricity and in fact currently accounts for up to 96% of the renewable energy in the United States. Hydroelectric power generation has the advantage of being able to create large amounts of electricity while producing zero pollutants. It burns no fuel during operation so there is no air pollution and it puts nothing into the water or soil. Outside of the impact of producing concrete and other construction materials hydro power would seem to be the ideal solution to our electrical needs. But what environmental impacts come with hydro power? Everything man-made comes with a price. This article will examine the environmental impact of hydroelectricity.

Hydroelectricity Dams: Impact on Land

Lake Mead has a "bathtub ring" effect from the changing water level caused by Hoover Dam.

Lake Mead has a "bathtub ring" effect from the changing water level caused by Hoover Dam.

Building a hydroelectric dam is a huge undertaking. For example, the construction of Hoover Dam, the most famous hydroelectric dam in the United States, produced a tremendous amount of land damage. While the construction firms were busy building Boulder City, Nevada to house the work force, it was necessary to divert the Colorado River from its natural course. Four diversionary tunnels 56 feet in diameter and nearly 3 miles long were blasted through the canyon walls. These tunnels were later incorporated into the dam and form the main bodies of the dam’s spillways. With the river diverted, precautionary cofferdams were built upstream to protect against the river accidentally flooding. The upper cofferdam alone was 96 feet high, 750 feet thick at its base, and contained 650,000 cubic yards of material.

Additionally, two massive concrete plants were built to supply the construction effort, as well as dedicated railways and a series of aerial cableways to move the concrete from each plant to where it was needed on the dam. In all, 4.4 million cubic yards of concrete were used in the construction of Hoover Dam. The dam created Lake Mead by flooding 247 square miles of land behind it. It took 6.5 years to fill Lake Mead, a requirement to prevent small earthquakes from the land settling under the weight of the water. Lake Mead submerged a massive area of land below water which is the most significant impact of hydroelectricity on land, it eliminates it.fail

Even though some dams are built to prevent flooding and increase usable land downstream they occasionally fail causing even larger floods. The video below shows the failure of the Teton Dam when a reservoir wall developed cracks and eventually burst.

Hydroelectricity Dams: Impact on Water

Tellico Dam was delayed for more than two years over legal trouble caused by concerns over the impact to an endangered species, the Snail Darter, shown here.

Tellico Dam was delayed for more than two years over legal trouble caused by concerns over the impact to an endangered species, the Snail Darter, shown here.

The construction of Hoover Dam had a profound impact on the ecosystem of the Colorado River. The river delta estuary once had a saltwater/freshwater mixing zone that reached 40 miles south of the river’s mouth. While the dam was filling, almost no fresh water reached the mouth of the river, allowing salt water to flow upstream. The Colorado River now has an inverse estuary with high salt levels closer to the mouth of the river. Native fish populations were destroyed and four species are currently listed as endangered.

Things become worse if a dam in constructed in an area with high levels of vegetation. When the reservoir behind a dam fills, plants, trees, and leaves, or biomass, will begin to rot. When the Nam Leuk Hydropower Project in Laos was completed, the rotting biomass caused an immediate drop in water quality. The artificial lake created habitats for disease-carrying mosquitoes and snails, increasing the likelihood of outbreaks of malaria, dengue fever, and schistosomiasis. Water quality deteriorated to the extent that useful species of fish disappeared and were replaced by undesirable ones.

Removing the biomass comes with its own problems. The most obvious solution to removing such a huge amount of vegetation would be to cut and burn it. The problem is that burning biomass releases greenhouse gasses into the air. Nutrients such as nitrogen and phosphorous are also released from burning biomass, which in turn would facilitates the growth of bacterial and algae blooms when the reservoir is filled. This can cause a chain reaction of water quality problems that may never go away. Reduced oxygen levels produce fish kills, cyanobacteria release toxic metabolites, and reservoir sediments release toxic substances such as mercury and hydrogen sulfide.

Another unforeseen problem relating to hydroelectric dams and water is droughts and geological changes triggering earthquakes and landslides. The video below outlines these effect after the building of the three gorges dam on the Yangtze river, China.

Environmental Impact of Tidal Power

Perhaps the cleanest form of hydropower, tidal power generation is not without its own environmental problems. A tidal barrage is a dam-like structure that is built across a river estuary to take advantage of the ebb and flow of the tides. Rather than retaining the water, however, a tidal barrage allows it to pass freely through a series of turbines to produce power. A barrage built across an estuary will have a significant impact on the water in its basin (the area upstream of the barrage) and on the fish population as well.

Less water is exchanged between the basin and the sea, reducing the amount of matter suspended in the water (turbidity). As turbidity decreases, sunlight is better able to penetrate the water, creating ideal conditions for the growth of phytoplankton. A larger plankton population causes a ripple effect up the food chain and affects the entire ecosystem. Another result of the decreased amount of water exchange is that less salt water is allowed into the basin, reducing salinity and again affecting the ecosystem particular species that prefer brackish water.

Water flowing down stream toward the sea carries high amounts of sediment with it. This sediment could build up behind and within the barrage, affecting the environment and possibly the operation of the barrage itself. Any pollutants flowing downstream may also become trapped behind the barrage and can become concentrated. If those pollutants were biodegradable, the resulting growth in bacterial may impact human health and the ecosystem.

Fish attempt to swim through the turbines with dire results. When the tides are not moving and the turbines are idle, all is well. When the turbines are in use, however, fish can be sucked into them. The mortality rate for fish passing through a turbine is approximately 15%, which can be devastating for fish that move to and from the basin every day. So far, an effective solution to allow the safe passage of fish around a tidal barrage has yet to be developed although some barrages try to discourage and redirect fish populations through specially designed passages.

Below is a video outlining and discussing the above issues. Is tidal power as “green” as we think?

Hydroelectricity: Environmental Impact Summary

Although it is considered a clean source of energy, hydroelectric power is not without its environmental problems. The construction of a dam is a tremendous undertaking, one that will leave the footprint of man scarred onto the area for generations. The habitats of many creatures are destroyed by the immense amount of work that goes into building one. Greatest among these causes for concern seems to be water quality issues that arise when the reservoir is filled. If the biomass is not properly removed, the gases released by its decomposition could create an environmental disaster for both humans and animals.

If properly implemented hydroelectric power is one of the cleanest and cost effective ways of producing electricity in the long run. It uses no fuel and produces no pollutants. The cost of producing hydroelectric power is constant. The infrastructure is built to last; dams can last for decades with the proper maintenance. If proper care is taken to protect the environment at the start of a hydroelectric project impact can be minimized.



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