Environmental-impact assessment of dams and reservoir projects (Review and a case study)

Dams and reservoirs are among one of the most sensitive of all development projects, in terms of pervasiveness of their influence in altering the environmental conditions and resources. In the present study, major dams and reservoir projects are reviewed, from the environmental point of view. Dams and Reservoir projects bring about major changes in the immediate environment, thus affecting public health, settlements, farmlands, roads and historical sites. Impacts on human population and wildlife may be profound. Tropical diseases, involving fresh-water hosts or vectors in their transmission, are often common around new reservoirs. Large lakes create limnological changes, excessive evaporation, seepage, and disturbance in water table and increased tendencies of landslides and earthquakes. Micro climatic changes are possible, such as fog formation, increased cloudiness and modified rainfall patterns. Retention of sediment results in silting up o f reservoirs. Water shortages on mountain rivers may leave unsightly dry riverbeds below a dam. Sediment deposition and growth of vegetation in reservoir affects the water-extraction for navigation, power-generation and fishing. Various dams and reservoir projects in the world are critically studied, in terms of creating environmental impacts. The Kalabagh Dam project (Pakistan), which is ready for construction, has been analyzed as a case study, by matrix method. Analyses show that adverse effects of this dam are less than the benefits. It is recommended that based on the experience, appropriate lines and strategies may be drawn up to evaluate the local projects. Multidisciplinary experts need to be involved, for assessing environmental impacts and suggesting mitigation measures, to combat the adverse effects.