Dams Advantages And Disadvantages

According to the The Report of World Commission on Dams, 2000; 46% of the water of the 108 significant rivers around the globe first flow to a reservoir and then make their ways to a natural waterbody or to the sea (WCD, 2000). It has been estimated that by the end of the twentieth century approximately 45,000 large dams were exploited across the world on the purpose of producing hydropower, delivering irrigation and safeguarding drinking water (Wei et al., 2008; Wildi, 2010). The high rate of progress in terms of establishment of dams, is due to its role in economic advancement. Nonetheless, the price the surrounding environment and society pay for the so called economic development, is making dam construction a problematic issue.

Why the

When an artificial reservoir is built, it is likely to change the natural way of operation of the entire ecosystem around it. River systems are interconnected hence, when a process takes place upstream, it can affect the condition around the downstream. Thus, the construction of a dam can cause significant disturbance to the whole ecosystem of the river. Loss of aquatic biodiversity takes place that hampers the balance of marine ecosystem, both upstream and downstream. Inundation occurs in upstream of the dam which results in loss of wildlife habitats, forest lands, species populations (McCartney et al., 2001). Dams also disrupt the movement of species along the river channel. It has been reported that around 5 to 14% of the salmon fishes dies while passing the Columbia River of Canada (Manatunge et al., 2001). Due to lack of discharge downstream of the dam problems like salinity intrusion, coastal erosion, riverbed scouring takes place affecting the ecological balance of the entire system (Wildi,

The water of a reservoir stands still where plankton can thrive resulting in higher turbidity. Moreover, mosquitoes and other water borne insects can reproduce. The chemical properties of flowing water and stored reservoir water are dissimilar to each other. Various chemicals mix with reservoir water, mostly through human activities. Metals such as zinc, copper, mercury, lead are often introduced to the reservoir water both in particulate and solution form (McCartney et al., 2001). The metal particles settle down at the bottom of the reservoir whereas the dissolved metals may get consumed by marine organisms affecting the food chain. Other chemicals, such as nutrients like phosphorus, reach the reservoir from nearby vegetation and croplands resulting in eutrophication. Studies have also reported that the self-purification ability of the water of a reservoir gets affected in the long run. In a study based on Manwan dam in China, it was evident that the amount of BOD, COD and NH3-N increased because the self-purification capacity reduced (Wei et al., 2008).

The water quality of the river stream gets affected by the temperature variations of stored water and the flowing water. The temperature of water is considered as a significant parameter to evaluate the impacts of reservoir on downstream