Large dam projects have played a key role in supporting societal development in the past and continue to be launched, primarily in developing countries. However, large dam projects also cause extensive environmental impacts in the river system, which may reduce the river system's capacity to provide goods, services, and other values apart from those generated by the project. The Environmental Impact Statement (ElS) has become a key instrument for enabling prevention, minimization, and mitigation of significant adverse environmental effects of major projects in early planning. The potential of EISs to support compromise building between conflicting interests is also increasingly recognized. In reality, the great potentials of the ElS are rarely fully utilized, which motivate further improvements.

This thesis has three main objectives, Le. (i) to examine the motives behind large dam projects, their impact on project planning, and some constraints for full project realization, (ii) to identify shortcomings in EISs and other project-related reports regarding the extent to and manner in which potential environmental effects of large dam projects are attended to, and (iii) to suggest measures for how to improve the capacity of EISs to support impact minimization and compromise building in project plarming and decision-making.

Based on a case study on the Southeastern Anatolia Project (GAP) in southeast Turkey, it was found that the objectives and planning of large dam projects can change significantly over time, in response to changes in the underlying ambitions and motives for development. While changes to the design may increase the dam's technical capacity to store water and generate hydropower, the actual potential to utilize its installed capacities during recurrent droughts may be limited. An increased scale and number ofdam project objectives may also lead to increased competition over the river water. Full realization of dam project objectives may be hampered by the climate and by growing water demands of competing uses. Moreover, an analysis of GAP-related reports revealed imbalances in the total degree of attention given to individual environmental problems, different categories of environmental problems, and to environmental problems of dam projects and irrigation schemes, respectively, as weIl as shifts in the focus of attention over time from early plarming to implementation. The fmdings suggest that project-related reports tend to focus on problematic environmental conditions that motivate project implementation, and on potential environmental effects that may undermine project productivity, viability, or longevity, particularly in planning and early implementation. In contrast, those potential environmental effects with no apparent bearing on the financial or operational success of the project tend to be largely neglected unless strong incentives are created.

The analysis ofEISs of large dam projects revealed shortcomings in the attention given to root causes and impact pathways involved in the generation of higher-order environmental effects and cumulative impacts. Important imbalances were also found in the degree of attention given to different types of environmental effects. In order to improve the capacity of EISs to explain how higher-order effects and cumulative impacts may arise, network analysis and cause-effect diagrams should be increasingly adopted. This thesis also proposes a conceptual framework to facilitate a comparison of desired and undesired effects, based on the view of a river system as a provider of goods and services, which enables the translation of ecological effects into their societal and economic implications.