Study On Multicriteria Decision Analysis For Dam Decommissioning

Decommissioning is an important stage in dams' life cycle, as well as an inevitable choice for China, where many dams have structural deficient, function and economic obsolescence, and ecosystem degrades due to dam construction and operation. While there were more than 1,600 dams that were decommissioned before the end of 2000 in China. When an increasing proportion of dams are approaching or exceeding their designed lifespans, and public awareness on dam risk and environmental conservation is being raised, the desire for dam decommissioning will be increased. However, dam decommissioning progresses slowly in China, because decision-making on dam decommissioning is a complicated problem, as well as no systematic and complete approach for guiding such kind of decision-making exists. So, it is imperative to study on decision-making approach to dam decommissioning to promote dam decommissioning in China.This goal of this study is to develope a decision-making approach for decommissioning of medium and small size aging dam in urbanized area of China, based on the theories of multi-criteria decision making (MCDA), flood risk assessment, and ecosystem service evaluation. This approach is suited to dam-decommissioning realities in China, and has systematic and complete characteristics. Analytic Network Process (ANP) is chosen to develop an ANP/BCR model which consists of three sub-networks, that is benefits, costs, and risks. Besides traditional advantage of qualitative assessment in ANP, this model lays emphasis on incorporating results of quantitative research on dam decommissioning, to increase rationality of decision-making, and flexibility of application. So, this model can be applied to dam-decommissioning cases with different key factors. Analysis of flood risks in dam-decommissioning is interdisciplinary. This study develops a framework for analyzing spatial multicriteria flood risk. It provides a concept framework for incorporating multidisciplinary researches into eliminating adverse effects on flood management caused by dam decommissioning. In order to investigate ecosystem service evaluation in dam-decommissiong decision making, this study applies a double-bounded dichotomous choice contingent valuation method (CVM) to estimate value of reservoir recreation which is the major ecosystem service related to dam decommissioning at the present stage of China. Using a traditional Logit model and three Logit models taking account of income restriction on willingness-to-pay (WTP), sensitivity of WTP estimates to the right tail of its distribution can be examined, thus increase statistical efficiency of WTP estimation.The developed approach is applied in a typical case, which is the Heiwa Dam, located in Chuzhou City, Anhui Province. Flood risk, and reservoir recreational value is analyzed for three alternatives, that is, exiting-condition, dam decommissioning, and dam rehabilitation. The results of flood risk analysis show that the dam rehabilitation scenario had a higher rank for decreasing the flood risk than the other two alternatives, but that it alone might be of little help in abating flood risk. It is also indicated that the flood control capacity of the dam is limited; thus, if the dam were to be decommissioned, the mean risk would not be greater than the current existing risk. As a small-sized dam, the total recreational value of the Heiwa Dam is 3 782×104 Yuan (95% confidence interval:3 296×104 to 4 355×104 Yuan) evaluated by CVM. These results indicate that the decision-making not considering values of ecosystem service may ignore important parts of values, and cause wrong decision. These quantitative results are incorporated into ANP/BCR model to appraise and rank alternatives. Priority ranking results show that the dam rehabilitation alternative maintains the highest ranking, exisiting-condition alternative is in the middle, and the dam decommissioning alternative is in the last. Sensitivity results reveal that the rankings are almost independent of changes in the weights associated with sub-networks; thus the ranking is robust. The low priority of the dam decommissioning alternative is due to its low benefits. These results have been approved by dam owner and local water conservancy department, and the Heiwa dam has been rehabilitated in 2010. It is indicates that the approach developed in this study is applicalbe to typical dam-decommissioning cases of multicriteria decision-making, and obtained results are rational.