Levelling and GPS networks to monitor ground subsidence in the Southern Po Valley

After a short historical introduction to the problem of the subsidence in the Po Valley, some results are shown of levelling campaigns carried out by various authorities or agencies in recent years, mainly in the southeast part of the Po Valley. We also present the results obtained along the coastline using the GPS technique both in a static and in fast-static modes. Attention is focused on the problem of the homogeneity of data from different sources, different periods and using different reference benchmarks. To overcome these problems, we propose a general levelling network covering the whole area of the valley, south of the Po river, connected with a GPS network of more than 50 points. This network will represent a spatial and temporal reference framework for all the measurements made in the past and for those planned for the future. A data information system has been implemented in order to organise and manage all available data in a well defined and homogeneous framework. This system will make it possible to store other related data, such as the pattern of the water table, geological evidences, land use, etc.