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Water resources management at Moires watershed in Heraklion using the Bayes Risk methodology

Varsamou Ioanna

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Summary

Over-pumping of groundwater is a common phenomenon in semiarid and coastal areas. The basic reason is poor water resources management plans. In this thesis the study area is the ​​Mires basin of western Messara watershed, located in Heraklion, Crete, Greece. The aquifer level has dropped significantly the past 30 years due to overexploitation. The Messara plain is characterized by strong agricultural activity and is in great need of irrigation water. An optimal environmental strategy is necessary to cover these needs. Therefore, a construction of a reservoir is proposed to collect the rain water and runoff, while water transfer is considered in case of dry years with extra financial cost. The decision dilemma is whether the proposed environmental policy is riskier than the existing policy that considers the use of groundwater only.The proposed environmental policy competes against high groundwater overexploitation fines, the lost value of groundwater and the pumping cost. The method used to assess the decision dilemma was Bayes risk. In Bayes theory the unknown parameters of the risk functions were calculated using prior functions derived from measurements of the study area. Prior functions related to the unknown probability of over-pumping were given by the binomial distribution and the posterior by Beta distribution for two different loss function scenarios. The probability of dry year was also estimated according to the rainfall data of the area in order to calculate the water transfer cost in case the reservoir fails to provide sufficient reserves. Four tests were performed for each of the two scenarios, changing the factors that affect the reservoir cost in order to get the optimal outcome. Thus, it was determined the optimal reservoir capacity compared to the penalties that occur from the positive over-pumping audits. The right combination of the two actions is the one that balances the economic benefits of society and the sustainability of the groundwater and the environment.

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