The Po: Centuries of river training

Abstract

The Po river drains the largest morphological unit of the Italian territory. River training works started in the lower Po during the Roman Age and developed upstream, first as discontinuous systems, then connected to form two uninterrupted belts, which have reduced the overflow frequency but also the storage capacity of the river flood bed. The outcome is an increasing value of the flood peak with given probability in the lower Po, which is the reach with the higher flooding risk. On the other hand, the upstream catchment, in which the river is provided with partial embankments, recently experienced a flooding event and require some form of protection. A risk mitigation policy should perceive and take into account all the components of the river system and their connections. In this perspective the development of traditional structural protection along the Po river has reached a critical stage; a further expansion of the existing levee system increases the down-stream risk. From the viewpoint of non structural protection, the river morphology and the past experience suggest that, based on rainfall and discharge monitoring, early warnings of flood hazards can be provided to communities that could be affected by such occurrences. Finally, to reduce the flooding risk in the lower Po a reduction of the flood discharge entering this reach is needed. This can be obtained by diverting the higher part of the flood from the river immediately upstream of the lower Po, allowing the inundation and the temporary storage of the diverted water on pre-designed large agricultural areas. Implementing such a policy will require a reliable system of flood warning and, above all, a sound regulatory authority.