Morphodynamics and flood control. A case study: Cittadella bridge in Alessandria.

The paper deals with a research project funded by AIPO concerning the morphodynamics of the Tanaro River and its influence on flood protection. Here, attention is particularly focused on a reach of the river most critical from the point of view of defending the city of Alessandria from the risk of flooding. This reach is characterized by the presence of several bridges, including a fairly old one, the Cittadella Bridge, that imposes a major constrain on the flow due to the unnaturally high elevation of the apron protecting the bridge piers. Moreover the reach planimetry displays strong fluctuations of channel width. In this paper we show the effectiveness of some fairly simple and low cost regulation measures, consisting of lowering the elevation of the apron of the Cittadella bridge and recalibrating the channel. Such countermeasures are straightforward suggestions arising from a study of the morphodynamic equilibrium of the stream. It is shown that they lead to a significant improvement of the conveyance capacity of the river in the reach crossing the city of Alessandria.