The Environmental Impact of Water Reservoirs (Essay Sample)

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The Environmental Impact of Water Reservoirs
The history of water reservoirs dates back to around 2950-2750 B.C when the first dams were constructed on rivers Tigris and Euphrates in Mesopotamia. Notable reservoirs of this period include the Jawa Dam in Jordan, Sadd-el-Kafara Dam in Egypt, and the Great Dam of Marib in Yemen among others (Chen 11). Then and today, the provision of water for domestic, industrial, and irrigational uses remain the leading reasons for reservoir constructions. Despite these benefits, the accumulation of water behind dams and consequent disruptions in the flow of rivers result in numerous positive and negative impacts on the environment. These include ecosystem fragmentation, sedimentation, river-line erosion, the spread of diseases, dam failures, resettlement of human populations, and flood control.
Erecting barriers across rivers breaks the downstream flow of water. This affects river ecosystems in various ways. For animals that depend on migratory trends in the separated ecosystems, part of their habitat gets cut off. Examples of these organisms include salmon and trout among others. When rivers flow freely, sediments facilitate the formation of depositional features like braided rivers, oxbow lakes, and deltas. Dams block the sediments and reduce the chances of such features getting formed. The increased accumulation of sediments within the reservoir reduces its water capacity and deprives aquatic ecosystems of the remaining habitat within the reservoir. On the other hand, the downstream sections of the river beyond the dam experience increased river line and coastal erosion that eliminates depositional features and their benefits to ecosystems (Dykes, Mark, and John 22).
After the construction of dams, reservoirs sometimes consume unexpectedly large tracts of land. This affects both human and animal populations that have to be resettled to give room for manmade lakes. Historical examples of such resettlements include the Three Gorges Dam in China, and the Aswan Dam in Egypt, which resulted in the migration of over a million people and the reconstruction of a temple respectively (NuМ€sser 9). Other negative effects of water reservoirs on human and animal populations include the spread of diseases and dam failures. The former occurs because the dams form suitable breeding grounds for vectors like mosquitoes and snails, which cause malaria and schistosomiasis respectively. Other waterborne diseases caused by the presence of reservoirs include cholera, shigellosis, hepatitis A, dengue fever, leptospirosis, and typhoid fever (Chen 50).
Additional negative and positive environmental effects relating to dam structures include dam failures and flood control respectively. In cases where constructors underestimate physical factors such as the resulting pressure from the water behind dams, the weight overwhelms the dam and it breaks down. Large volumes of water released downstream flow indiscriminately to destroy property and claim lives. Previous dam failures include the 1975 Banqiao Reservoir Dam disaster in China and the 1928 St. Francis Dam failure in California (Nersesian 292). On the other hand, dams assist in containing floods and controlling their negative effects. Floods from the Yangtze River in China displaced 18 million people in 1954 and another 180 million in 1998. Howev...