Environmental consequences of hydroelectric development: The role of facility size and type

The development of hydroelectric power throughout the world is receiving renewed attention as the economic, political, and environmental costs of conventional energy production rise. There is currently a perception that hydroelectricity has environmental and economic advantages over electricity produced by conventional energy technologies, but there is a paucity of information about the environmental impacts of hydroelectric facilities as a function of size and type. We characterize the environmental impacts of hydroelectric developments and quantify these impacts as a function of the size and type of project. Several unexpected conclusions arise from our analysis. For most hydroelectric facilities, size, as measured by installed capacity, is not necessarily a good indicator of the severity of environmental costs. For impacts such as land flooded and evaporative water lost, smaller facilities cause greater environmental disruptions per unit of energy produced than do larger facilities. A more striking conclusion, however, is that differences in the type of facility, as indicated by the relationship between dam height and gross static head, are often far more important from an environmental perspective than are differences in the installed electrical capacity of a facility. Another major conclusion is that the development of hydroelectric facilities (independent of their size) such as dams at new sites and dams operated to produce peak power are often accompanied by environmental and ecological disruptions comparable to or exceeding those of conventional non-hydroelectric energy facilities. These results suggest that there is no justification to expedite licensing procedures for hydroelectric facilities smaller than some arbitrarily chosen installed capacity, as currently permitted by some laws. Appropriate policies should emphasize the development of dams on the basis of other favorable physical, chemical, and biological characteristics.