For centuries now, dams have been built by humans. It is only recently that attention has been put into determining the environmental effects of dams though. A dam is built across a body of water, often times a river. This large wall is meant to control the flow of water. As the water is changed, so are the various life forms that interact with and depend on this water. Water works to shape an ecosystem and when the flow of water is altered, the ecosystem is also altered. Thus, there are environmental effects from the construction and use of dams. Some of these effects can be considered negative while others can be considered positive. This essay will explore both the negative and positive environmental effects of dams.
One of the most daunting environmental effects that occur during the construction of dams is earthquakes. During the construction of a dam, the large walling of the river slowly begins to block water from upstream. This creates a large lake-like body of water above the dam. This collection of water is better known as a reservoir. As the water fills the reservoir, great pressure is created (Yardley 3). The added stress on the land can cause “a major earthquake induced by pressure from the rising water” (Yardley 3). These earthquakes that result from the construction of dams can destroy the surrounding land and greatly damage the populations of wildlife.
The creation of the reservoirs themselves also causes another negative environmental effect. As the water fills the reservoir, it floods the areas surrounding the reservoir that was previously land. As a result, “Reservoirs have flooded vast areas — at least 400,000 square kilometres have been lost worldwide.” (McCully) That number is equivalent to 248.548 square miles. A large amount of this land was very beautiful land that is now lost. One example of beautiful land that was almost lost due to the construction of a dam was “a proposed hydroelectric project in Silent Valley”, India (Krishna 217). This land was “an uninhabited, biologically-rich tropical rain forest, one of the last remnants of its kind in the country.” (Krishna) Such a beautiful and rare ecosystem for the area would have been a great loss to the world. Luckily, the people were aware of the rarity of this land and the project was halted (Krishna 217). Sometimes, humans need to look past the usefulness of land just to them and see how the land is useful to all of Earth.
The quality of land is important as well as “river and floodplain habitats are some of the world's most diverse ecosystems” (McCully). The reservoirs also kill the vegetation and wildlife that was living on this land. It is difficult to give an exact number concerning “how many species of plants and animals are now extinct because their last habitat was flooded by a dam but the number is likely far from negligible.” (McCully) The saving of wildlife and biodiversity needs to be considered to stop these extinctions from continuing. Reservoirs also cause humans living in the area to have to move. Their living areas will be flooded by reservoirs. Sometimes, the humans are paid for their land, but other times they are not.
Once the dam is created, it cuts off the water supply and migration patterns for various animals (McCartney 128). Some fish end up trapped in the reservoir above the dam. Others will end up trapped downstream as they are unable to move upstream past the dam. Some of the fish trapped in the reservoir cannot survive as they are not used to a lake-like habitat (McCartney 128). Other fish thrive in such a habitat and survive (McCartney 128). However, “The number of fish species which thrive in the relatively uniform habitats created by reservoirs is only a tiny fraction of the number which have evolved in the diverse niches provided by rivers.” (McCully) So, the reservoirs end up having an overall negative effect on the environment.
As stated by Matthew McCartney, “Downstream of dams, marked changes in fish populations occur as a consequence of blockage of migration routes, disconnection of the river and floodplain, and changes in flow regime, physiochemical conditions (e.g. temperature, turbidity and dissolved oxygen), primary production and channel morphology. These changes may benefit some species but they generally have an adverse effect on the majority of native species.” (128)
So, both the fish trapped upstream of dams and downstream of dams experience negative consequences due to the environmental effects from the presence of dams. Land-based animals also suffer due to the migration disruptions caused by dams. It hinders their abilities to find food and “leads to the risks of inbreeding from a smaller genetic pool.” (McCully) The decrease to the fish population will result in a decrease of the population of animals dependent on fish for food. Herbivores will also suffer from the loss of vegetation due to the decrease in water flow as they are unable to easily move to find other food sources. The inbreeding of these animals over a period of time can cause mutations that will disrupt the cognitive and physical development of them. Often times, the control of water prevent it from ever reaching the river’s mouth. Such an event will cause a large drying out of the mouth area and the loss of both vegetation and animal life. It will also make the area unsuitable for human life. It will appear to almost become a desert.
Dams cause a disruption to the flow of sediments along the rivers (McCartney 125). Sediments (or rock-based minerals) naturally flow down a river. So when dams block the flow of water, they are also blocking the flow of sediments. Sediments will become trapped above the dam and pack at the bottom of reservoirs. “It is estimated that between 0.5% and 1% of the storage volume of the world's reservoirs is lost annually due to sediment deposition” (McCartney 125). As a result, dams even cause negative environmental effects to themselves. As the sediments are stuck upstream of the dam, the amount of sediments downstream is scarce. As a result, “Downstream of a dam, reduction in sediment load in rivers can result in increased erosion of riverbanks and beds, loss of floodplains (through erosion and decreased over-bank accretion) and degradation of coastal deltas.” (McCartney 125) So, the lack of sediments can cause further loss of land than just through the creation of reservoirs by dams. Such erosion can also lead to landslides as is predicted with the Three Gorges Dam in China (Yardley 1).
Dams due offer some arguably positive environmental effects, one of those being the generation of electricity. This type of power generation is known as hydroelectric. As a result, the dams that produce this power are known as hydroelectric dams. As the water flows through hydroelectric dams, turbines are turned by the flow and the resulting kinetic energy is turned into electricity. This energy is renewable as the water flow can be reused repeatedly to produce electricity. Also, “hydropower does not consume or pollute the water it uses to generate power, it leaves this vital resource available for other uses.” (Yuksel 103) Adding to that, “Hydropower has very few greenhouse gas emissions compared with other largescale energy options.” (Yuksel 103) So, it can be argued that this is a positive environmental impact in that it not only directly impacts the environment hardly at all, but is a substitute for other power generation methods that cause large amounts of pollution to damage the environment. It also offers a possible solution to current dams that are seen as having negative environment effects. Rather than just tearing down these dams, it has been discovered that 64 of the dams in the United States currently not generating hydroelectric power could be altered to generate the power (Myron 14). As a result, this could work to counter some of the previously discussed negative environmental effects of dams.
The control of water flow by dams offers numerous positive environmental effects. Dams could work to balance the harsh conditions an ecosystem experiences on a yearly basis. One example of this is that “by storing water during rainy seasons and releasing it during dry ones, dams and reservoirs can help control water during floods and droughts.” (Yuksel 103) This control could work to protect the lives of humans, vegetation, and wildlife. From the aspect of human survival, dams alter the environment to support “essential water services such as irrigation, flood control, and drinking water supplies.” (Yuksel 103) As a result of dams, humans are able to survive in ecosystems that they would otherwise die in. Dams also allow for easy navigation along rivers and help in transporting goods (Yuksel 103). All of these environmental effects that benefit humans should be considered positive effects as they promote mankind’s existence.
Some of the positive and negative environmental effects of dams have been explored within this essay. Although the negative effects are substantial, the positive effects to the environment cannot be ignored. There are individuals who view the destruction of land, vegetation, and wildlife and argue for the destruction of dams. However, there are individuals who views the positive environmental affects dams have for humans and the environment and as a result argue to continue building and using dams. A third viewpoint exists as well that argues for the continued use of dams, but for the minimizing of the negative environmental effects. Possible solutions include the placing of sediments downstream to reduce erosion, alternate paths for the migration of fish and land-based animals, transportation of animals before the filling of reservoirs, and the creation of artificial floods to promote water flow and life downstream (McCartney 130-131). Other similar solutions exist as well. No matter what viewpoint an individual uses, dams control a valuable element and result in various positive and negative environmental effects.
References
Krishna, Sumi. Environmental Politics: People’s Lives and Development Choices. California: Sage Publications, 1996, Print.
McCartney, Matthew. "Living with dams: managing the environmental impacts." Water Policy 11.s1 (2009), 121-139.
McCully, Patrick. "Rivers No More: The Environmental Effects of Large Dams." International Rivers. International Rivers, Web. 1 Feb 2010. http://www.internationalrivers.org/en/node/1636
Myron, Levin. "INNOVATE: CLEAN POWER THAT'S EASY ON THE ENVIRONMENT." Sierra 95.1 (2010), 14-14.
Yardley, Jim. “Chinese Dam Projects Criticized for Their Human Costs." New York Times November 19, 2007: 1-5. Web. 1 Feb 2010. http://www.nytimes.com/2007/11/19/world/asia/19dam.html.
Yuksel, I. "Dams and Hydropower for Sustainable Development." Energy Sources Part B Economics Planning and Policy 4.1 (2009), 100-110.
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