Mapping regional land displacements in the Venice coastland by an integrated monitoring system

Abstract

An original integrated monitoring method is designed to infer an accurate and reliable figure of regional land displacements in coastal areas where the presence of internal waters, wetlands, farmlands, urban and industrial centers usually reduces the efficiency of single ground-based and satellite-based measuring techniques. Five different methods, i.e. spirit leveling, Differential Global Positioning System (DGPS), Continuous GPS (CGPS), Interferometric Synthetic Aperture Radar (InSAR), and Interferometric Point Target Analysis (IPTA), are integrated into a Subsidence Integrated Monitoring System (SIMS) to overcome the limits characterizing each technique. The SIMS has been used over the past decade to provide a new image of the land displacements in the Venice region. The result exhibits a resolution never obtained before. The central lagoon, including the city of Venice, shows a general stability while the northern and southern lagoon extremities and their related catchment sectors sink with serious rates averaging 3 to 5 mm/year. The sinking rates increase up to 10–15 mm/year in the coastland south of the lagoon. Relatively small uplifts (less than 1 mm/year) are observed at the Alpine foothills and in a wide area comprised between the Euganean Hills and the lagoon. The observed land displacements have been associated to the geological features of the study region, i.e. tectonics, seismicity, differential consolidation of the middle–upper Pleistocene and Holocene deposits, and to anthropogenic activities, such as land reclamation and groundwater withdrawal.