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Multi Criteria Analysis for the definition of environmental flow from hydroelectric diversions within an IWRM framework

pubblicazioni - Presentazione

Multi Criteria Analysis for the definition of environmental flow from hydroelectric diversions within an IWRM framework

A fundamental requirement of the European Water Framework Directive is the maintenance of the hydraulic and ecological continuity of the rivers. In Italy, this requirement has been partially implemented by the entry into force of the norms which impose the release of the reserved flow at any surface water diversion by the beginning of 2009. The flows are defined locally according to the rules established by the Regional Authority on the basis of what suggested by the Hydrographic Basin Authority. Flows are usually based on formulas for the computation of some kind of percentage of the natural flow. This regulation accounts only partially for the water management approach requested by the WFD. Indeed two important issues are not addressed with this approach: 1) there is no active involvement of the main stakeholders and 2) the diversion is not set in relation to other possible uses of the water resource, as requested by the Integrated Water Resources Management that include not only water resources but the whole environment and spatial planning at an appropriate scale. In order to overcome the command-and-control approach provided by the regulation in force and meet the requirements of the WFD, the definition of the reserved flows should be based on a shared decisional process where different flow options are set and the subsequent scenarios are evaluated. The decisional process should be shared with all the stakeholders, involving them by the very beginning. In this paper we present a case study regarding the application of the proposed approach to a large scale experimentation, carried out in Valle d’Aosta, Italy. Valle d’Aosta is one of the most important regions in Italy for hydroelectric production. The Regional Authority has provided the possibility to define the reserved flow values on the basis of ad hoc experimentation, supervised by a technical committee formed by main stakeholder and with the scientific supervision of ERSE. The aim of the activity is the definition of environmental flows to be released from hydroelectric diversions through the involvement of the main stakeholders from the beginning and taking into account all the main consequences of different water policy. According to the last requirement, the first step is the definition of different water policies and the assessment of their consequences, possibly in terms of measurable criteria. Due to the complexity and extension of the problem, an experimental plan was defined in order to quantify the ecological changes caused by different hydrological regimes. The experimental plan is designed to single out the effects on ecological systems due the main sources of variability, namely: • Environmental flow requirements
• Spatial variability
• Temporal variability The first item is the main focus of the study and four increasing levels of release requirements were defined. In order to be able to detect ecological changes in river ecosystems, every release level is planned to be maintained for a whole year. Spatial variability was considered by defining three different areas within which geomorphologic characteristic are homogeneous. Temporal inter – annual variability was considered by defining, for every homogeneous area, two watersheds, one subjected to increasing levels of release requirements, whilst the other to constant environmental releases throughout the experimentation. Temporal intra – annual variability is considered with several experimental surveys during every year. As mentioned above, other consequences of environmental flow requirements are to be considered, from the energy loss to the increase of carbon dioxide emissions form thermoelectric power. A specific activity is being carried on for the assessment of the impact on river landscape. In this case the main difficulty is the definition of objective and possibly quantitative criteria. To this end, a contingent valuation method is used to estimate in monetary terms the impact of flow diversion by hydropower plant. Once the main effects of the diverse water policy alternatives are evaluated, the next step is the application of a methodology for their comparison. The presence of conflicting objectives prevent, in general, from the identification of the best alternative according to all point of view. Even limiting to environmental aspects, the demand for conserving the local river ecosystem is opposed to the request of limiting the use of fossil fuels in power generation. In order to be able to compare different water management policies and different point of view, we propose the use of multi-criteria analysis (MCA), which allows considering objectives that are in contrast with each other and that are measured with their own metric scale. MCA provides a methodology for comparing and ranking different outcomes; moreover its use forces the involvement of main stakeholder from the beginning and allows a transparent and shared process for decision making. This work has been financed partly by the Research Fund for the Italian Electrical System under the Contract Agreement between ERSE and the Ministry of Economic Development – General Directorate for Energy and Mining Resources stipulated on July 29, 2009 in compliance with the Decree of March 19, 2009 and partly by the EU Alpine Space Program through the project SHARE.

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