ABSTRACT
This chapter describes the nature of the impacts in general, supported by the Case Studies, the Cross-Check Survey and the Thematic Reviews on Ecosystems and on Global Change. The extent to which efforts to reduce or eliminate these impacts were undertaken in the past is described at the end of each discussion. It contains a assessment of past experience with efforts to avoid, mitigate, minimise or compensate these impacts. Current efforts to restore environmental function through decommissioning are also reviewed. Efforts to restore floodplain ecosystem functions rely on reversing the effects of the dam through a program of managed floods designed to simulate the floods that occurred prior to the dam. The WCD Knowledge Base provides a number of examples of the ecosystem enhancement effects of large dams. Downstream impacts on aquatic ecosystems and biodiversity and on floodplain ecosystems represent the sum of many complex interactions and thus are inherently difficult to predict where baseline data are absent or unreliable.
