The fundamental objective of constructing dams is to obstruct flowing water for benefit of human communities; flood control, hydroelectric generation and regulation of water supplies in urban areas are the primary advantages of dams construction. However, the construction of dams also affects the society and environment significantly.
Dams and Environmental Risks
The construction of dams poses significant and persistent effects on ecology of aquatic habitats; by transforming the flowing water into stagnant water, storage of water in reservoirs leads to changes in hydrological parameters such as levels of dissolved oxygen. The alteration in river hydrology impacts the ecological balance of the habitat causing changes in species composition and the number of fishes.
Further to changes in river hydrology, changes in river paths associated with reservoir storage blocks migration routes of certain aquatic species such as trout and salmon, leading to their elimination from the habitat.
Social Impacts of Constructing Dams
The most controversial consequence of constructing large dams is the massive displacement of people; as the scale of the dam increases, the scope, duration and intensity of its impact is amplified significantly. In fact, large dams such as three gorges dam in china have been responsible for displacement of large population of people.
The storage of water in reservoirs causes inundation of thousands of hectares of river line lands. In addition to the economic and social pressures of managing displaced people, the water storage in dams and the resulting higher evaporation rates increase the risks of adding salts to farming areas, thus making them unfit for irrigation due to increased salinity.
Further to the inundation of land, if a dam breaks, people and property downstream may be endangered considerably. Such an incident may cause an outbreak of waterborne diseases such as schistosomiasis throughout the local population.
Dams and Seismic Activity
A significant number of large dams around the world have been linked with reservoir-induced seismicity, earthquakes that may occur before and after filling a large reservoir behind the dam. The larger the reservoir and the faster it is filled, the greater the intensity of seismicity. In order to mitigate the risk of seismic activity, the site selected for a dam must not be located in a seismically active area.
Risks of Constructing Dams
Despite the associated benefits, there are several social and environmental risks linked with dams. The construction of dams causes hydrological and ecological alterations to the aquatic habitats resulting in elimination of animal species such as trouts and salmons. In addition, construction of large dams results in displacement of large populations due to land inundation. The seismicity linked with dams can also be catastrophic in some cases.