BONDESAN M.
Geomorphological hazards in the Po Delta and adjacent
Abstract
Man has played an increasingly important role in the geomorphologi-cal evolution of that part of the wide coastal belt occupied by the present and ancient deltas of the Po River. Over the centuries, man has identified and faced various types of geomorphological hazard, from flooding to the threat of silting-up of the mouths of the Lagoon of Venice by sediments discharged into the sea from the Po. In order to control the river network, first embankments were built, hindering sediments from compensating the effects of subsidence: the course of the Po has been diverted several times. Colonization was completed with the draining of marshlands and lakes. However, still today, this area faces a whole series of geomorphological hazards, some due to natural phenomena, such as geological subsidence and the eustatic rise in sea level, and others connected to man’s activities. The unnatural altimetric conditions caused by the stabilization of the river network have been aggravated by artificial subsidence, due to reclamation itself or to other activities altering the state of underground waters. At present, almost the entire territory is under sea level and drainage is only made possible by the constant efficiency of a large number of pumping stations. The risk of breaching, now well under control, is accompanied by possible flooding due to drainage difficulties and above all by invasion by the sea. In recent decades, yet another cause of hazard has been the reduction of solid transport by the river, again due to man’s activities (mainly gravel and sand quarrying from riverbeds). This reduction has given rise to a general tendency to beach and riverbed erosion, which not only considerably lowers the tourist value of the beaches but also increases the danger of invasion by the sea.