Impact of dams on river water quality

Dams are constructed on the rivers to meet the varying requirements of power, irrigation, drinking water and flood control. The foremost consequence of a dam project is creation of reservoir submerging large tracts of land, substantial amount of vegetation and bio-mass which undergoes decomposition taking on an average eight to ten years to degrade the initial stock. Change of aquatic system from riverine to lackustrine environment is, therefore, obvious. There is a consequent effect on the water quality due to alterations in the dynamics of oxygen transfer mechanism in the water of the river. In the impoundments having large depth, thermal stratification occurs dividing the vertical profile of the river in distinct zones known as epilimnetic and hypolymnetic zones. Water quality of the impounded river is characterized by impacts along the longitudinal profile of the river also both upstream and downstream of the dam. The quality of water deteriorates towards the reservoir bed and also upstream and downstream of the reservoir due to several factors such as duration of storage, the nutrient load, the depth of reservoir, the turbidity and temperature. This study is carried out to assess the variation of water quality due to dams. For the purpose of study three dams having different design features have been selected to assess the water quality along the vertical profile of the impoundments and along the longitudinal profile of the rivers upstream as well as downstream of the dams. Depletion in Dissolved Oxygen content was observed both in the vertical and longitudinal water quality profile of the river. Similarly metals like Lead, Copper, Zinc, Manganese and Iron showed increased concentrations in the bed level samples as compared to samples of flowing water.