Enel experience in the environmental management of maintenance of hydroelectric reservoirs

Abstract

Environmental concerns linked with extraordinary maintenance of hydroelectric reservoirs have been emphasized in ltaly in recent years. ENEL manages more than 240 hydroelectric plants fed by reservoirs mostly located in the Alps and in the Apennines (and so relatively unpolluted), for a power production of about 30 billions kWh/y. At present in ltaly there is not yet a specific national legislation that regulates these maintenance operations from the environmental standpoint, so the conditions for the grant of the permit for their execution are object of case by case negotiations with local competent Authorities. In the last years ENEL has been gathering experiences in monitoring the impact of emptying and cleaning reservoirs on the physico-chemical and biological characteristics of water downstream of the dams and in environmentally sound allocation of fine sediments, considering all available options (agricultural recycling, land filling, river bank and coastal reprofiling, downstream drifting, dumping). On the basis of the results of these surveys, combined with a review of other European and North-American works, guidelines for performing these operations in condition of environmental safeguard and for related monitoring have been defined with the aim to propose an uniform procedural scheme to all competent Authorities. In this paper the basic experiences and judgements for determining the relevant criteria of the guidelines are presented.