| Cascade Hydropower Development (CHD) in a river basin is an effective pattern to explore and make use of the water energy resources, and promoting CHD continuously has been an important energy strategy in China since 1981. However, over the past two decades, increasing concern have been attracted on the negative eco-environmental impacts (EIs) caused by hydropower projects. Compared with the EIs caused by a single station, the EIs caused by the cascade stations of a same river are more complex and broader. How to analyze and assess these EIs comprehensively, holistically and systematically, so that to strengthen the positive factors, control and even avoid the negative factors, will be the key to promote the sustainability of CHD in China.CHD in a river basin is a series of stations from the upstream to the downstream of the river, which could enjoy a joint operating regime as a group. Among these stations, one or more large-scale reservoirs will be settled down in order to deeply increase the regulating ability of the whole cascade. Hence, large reservoirs with high dams divide the continuous river into several discontinuous sections, so that compared with the single hydropower projects (SHP), the EIs caused by CHD are going to be more cumulative in temporal and spatial scale. In other words, the relevance among cascade stations of a same river may strengthen or weaken the EIs of a single cascade station, even a new "cumulative impact" would arise because of the interactions among these stations: cascade stations of the river, eco-environmental elements of the river basin, and the interactions among them have compounded into a complex system named "Cascade-compound Eco-environmental System".Compared with the respective researches with specific discipline, the EIs Analysis and assessment of CHD can be accomplished more effectively by establishing a more comprehensive and multi-disciplinary assessing theory and methodology framework on the basis of system science, especially the complex systems science. This theory and methodology framework can enhance the inner links among different research fields help to acquire the overall awareness on the EIs of CHD. However, the outcome of current study about the assessment of EIs for CHD in China mostly focused on specific disciplines, lacking of the overall analyzing and assessing model from system perspective. Therefore, there are both theoretical and practical values on the exploring of constructing overall analyzing and assessing model for EIs of CHD, it can not only reflect the trends of EIs assessment for the CHD, but also meet the need of sustainable development of CHD in China.This dissertation proposes an overall analysis and assessment model for EIs of CHD under the guidance of system science, and to explore the various types of system analysis and assessment methodologies suitable for this model. For one hand, more interdisciplinary, comprehensive and universal content could be included into the researching scope, so that the results of the dissertation can play a reference role in EIs evaluation of CHD. For the other hand, the EIs analyzing and assessing procedures of CHD are tend to be repeatable, easily maintained and easily computerized. The major jobs of this dissertation are as follows:(1) Large amount of national and abroad CHD cases have been summarized, the CHD has been compared with SHP in various types of eco-environmental elements to reveal the similarities and differences between them, hereafter, basic features of EIs of CHD have been extracted. Results show: 3 modes could be generalized to represent common strategy of CHD, they are mode of type I (leader - runoff compound), mode of type II (continuous reservoirs) and mode of type III (Low Dam-runoff). The negative EIs of CHD are more significant in several aspects, such as the fragmentation in the rivers, the river habitat alteration, the changes in self-purification capacity of water and the changes of watershed landscape pattern; but at the same time, the EIs of CHD can be more controllable. 3 basic features of the EIs of CHD are extracted, they are systematic, cumulative and controllability. A set of eco-environmental elements which could be influenced by CHD are presented, with the highlight of eco-environmental benefits and sensitive ecological problems.(2) A Cascade-compound Eco-environmental System (CCES) has been defined as the research object to implement the structured analysis and assessment of EIs of CHD, several typical scenarios which in accordance with the 3 basic modes of CHD have been designed, and for each scenario, a mechanism analysis has been accomplished to reveal the generating pathways of EIs of CHD. Results show: the CCES is a complex system; 5 typical scenarios are designed to represent the 3 basic modes of CHD, and for each scenario, its relevant mechanism analysis can depict the cumulative pathways of EIs of CHD; furthermore, it is necessary to promote the study of environment-restoration regime based on the controllability of EIs of CHD.(3) On the basis of mechanism analysis of typical scenarios, a structured retrospective assessment model for EIs of CHD has been established. First of all, a conceptual model and a evaluation process were proposed, secondly, an index system was developed, thirdly, a series of specific evaluation methods were proposed, and finally, "eutrophication" was chosen to be the evaluation target to construct the logical model of the structured retrospective assessment. Results show: choosing fuzzy mathematics to be the basic theory to decide the influence extent of the CCES is feasible and effective considering the current level of relevance data accumulation; the logic model based on UML is object-oriented, which having the obvious advantages of reusability and maintainability, so that it can be converted into a computer software conveniently.(4) On the basis of mechanism analysis of typical scenarios, a structured predicting assessment model for EIs of CHD has been established. An overall framework of this predicting assessment model was developed based on the combining of two system simulation methodologies, they are: the System Dynamics (SD) and the Agent-based Modeling (ABM). Finally, a predicting assessing case was displayed to solve the influence forecasting of immigration that originating from dams construction. Results show: mathematical models or statistical models can not describe the structure of a complex system effectively, whereas system simulation methodology can be an appropriate way to modeling the complex system; the structured predicting assessment model should be constructed through taking advantages of both SD and ABM, for both of them are general prediction and system simulation tools with mature simulation software; the overall framework model based on SD and ABM is an object-oriented model, which is flexible, and easy to be expanded and maintained; and finally, being a mature simulation software for SD, Vensim can solve a range of prediction requirements on EIs of CHD.In all, researching the analysis and assessment of EIs for CHD based on the (complex) system science, constructing the overall framework model for the EIs assessment and proposing the suitable and structured analyzing and assessing methodologies for this model, will help to improve the current lack of overall assessment model for CHD in China, and be valuable both in theoretical research and practical application. The results of this dissertation show: the theories and methodologies of complex system analysis and assessment can enhance the interdisciplinary, synthesis, comprehension and structuring of analysis and assessment of EIs for CHD, promote the integration and computerization of various aspects of the assessment, so as to provide reference for relevant research.
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