Hydrochemical effects of the 'Bilancino' dam on the Sieve River basin and interactions with the Arno River (northern Tuscany, Italy)

摘要

A hydrochemical study was carried out in order to detect some 1997 to 2002 changes in surface water composition of the catchment basin of the Sieve River. The Sieve River is the most important tributary of the Arno River with regard to the Florence water supply, as a consequence of the accomplishment of a broad artificial lake realized along the upper course of the Sieve. Moreover, the interactions between the Sieve and the Arno rivers were studied to highlight the influence of the former's discharge on the latter's water quality. An experimental classification for surface waters - developed in the Department of Earth Sciences of Florence - is used because of its excellent suitability to the whole Arno catchment basin. Two sampling surveys - before and after the dam's fulfilment - were performed, and the drawn waters were analysed to characterize their geochemical type by gauging fundamental components and environmental indicators. The analytical results point out a clear depletion in ionic concentrations following the lake realisation, with a general quality improvement of the Sieve waters inside and downstream of the reservoir. Moreover, a sort of hydrochemical stratification was observed in the water column, where contents seem to increase with increasing depth. Finally, the water supply provided by the Bilancino dam (up to 8 m~3/s for 180 days, during an average hy-drological year) will improve the quality of the Arno waters downstream of the merging with the Sieve.