La cascata delle Marmore: uno straordinario scenario per artisti di ogni tempo prodotto dalla necessità di mitigare il rischio idraulico del Lacus Velinus - Marmore Falls: an extraordinary artificial setting for artists of all times resulting from the need of flood risk mitigation of Lacus Velinus

The extraordinary scenery of Marmore waterfalls (near Terni, southwestern Umbria) is a rare emblematic case of the positive outcome of human action on a natural landscape. Marmore Waterfall is the result of several hydraulic interventions for improving the outflow of the Velino river into Nera river through the natural barrier originated in the last millennia by the development of continental carbonate deposits (calcareus tufa); which whitish colour and marble appearance is probably at the origin of the name “Marmore”. Despite its artificial/ anthropic origin, the spectacular leap of the waterfalls about 165 m high, inspired artists and scientists of all times. According to a recent research, Leonardo da Vinci himself might have been there in 1473, making the popular drawing “Paesaggio con fiume”. Marmore waterfalls is a balancing point opposing forces driven by climatic and human factors. The waters of the Velino river, rich in calcium carbonate, produced a large and thick deposit of calcalreous tufa, raising a natural barrier at the confluence with the Nera river. Such a process was modulated by climatic oscillations, with phases of construction during dry and hot periods, when the barrier grew up and the Lacus Velinus (wich occupied the northern and the central part of the Rieti plain) partially drained, and phases of erosion during cold and wet periods (when the calcalreous tufa were incised and the Rieti plain partially dried up). In 271 B.Ct the Romans opened the Curian trench, a man-made canal, aimed at diverting the stagnant waters towards the Marmore escarpment, reclaim the swampy Rieti plain and restrain the devastating floods of Velino river, but which in fact lead to the disappearance of the Lacus Velinus and transferred the problem of flood to the Nera river and the underlying Terni valley. What the Romans did gave rise to the first judicial dispute linked to a waterwork. The results of facies analysis of the deeply karstified, calcareous tufa of the Marmore plaque, might help to understand the geological components, and the evolutive framework of such a complex resulting from the interaction of natural and human processes.4n