The fluvial dynamics of the Arno River - 2. Historical evolution of the Arno river bed.

The study presents the result of research on the dynamics of the river bed in the past. The research involved finding and analysing historical maps and documents kept in the State Archives and libraries. This kind of documentation is of great interest for the study of the dynamics of the river. Even thought it is not homogeneous from a spatial and temporal point of view, it still constitutes an indispensable wealth of knowledge when we come to assess its evolutionary tendencies over the last few centuries and its degree of anthropical conditioning. For most of its course, the bed of the Arno River was affected by a series of canalisation, rectification and bank protection works (from the 18th century onwards in the middle-upper Valdarno area, during the first decades of the 19th century in the lower Valdarno area) which radically changed its form and hydraulic-morphological features. The evolutionary dynamics of the last century, which were greatly limited in a planimetrical sense by the partial training of the course by means of embankments and protection works, were predominantly altimetric in nature. They consisted in a generalised lowering process of the bed, which has created serious stability problems for the engineering works and the banks, and has triggered off regressive erosion phenomena in the tributaries.