Energia idroelettrica sostenibile e dinamica fluviale: le traverse sul F. Arno

Hydroelectric power can be produced traditionally by means of building of a dam with related reservoir. The basin on the hand can permit a more “elastic” management of production; on the other hand can hardly and negatively influence the riverbed dynamics, causing the “trap effect” affecting bedload transport. Before the coming of electric power, the stream power was used directly like hydraulic power, realising little steps by means of weirs and channels towards the turbines, in order to move mills, olive presses, forges, sawmills, paper mills and other factories. Such small structures, in the past, were not generally considered interesting in order to produce electric power as they are in the present. The weirs permit the realisation of small hydroelectric stations with flowing water. The structures on the hand don’t produce serious problems to dynamics of riverbed; on the other hand have to permit sediment transport (including gravel) downstream under all discharges, without problems to the machines or the equipments of water transfer and draining. The paper analyses the fluvial dynamics problems and the technical solutions regarding the hydroelectric use of existing weirs along Arno River (Tuscany, Central Italy). River Arno has a mobile, unichannel and gravelly riverbed. This one is substantially fixed, due to works of banks stabilitation realised in order to oppose its planimetric mobility. Some of these weir were recently builded and they prevent the hard erosional processes occurred during the last decades. The study is finalised to the correct planning of the works and to the definition of management, verifying that works and management could be compatible with river characteristics and sustainable without temporal limits. The used approach in the study, due to the lack of statistically valid data about solid transport (and, in particular, about the bedload transport) in the Arno River, is the morphological-sedimentary approach.