Ground surface dynamics in the northern Adriatic coastland over the last two decades

During most of the past century, spirit leveling was the only technique for providing high-precision data for the assessment of land subsidence in the northern Adriatic coastland. Only at the end of the 1990s did global positioning system methods, both continuous (CGPS) and differential (DGPS), begin to be used for ground movement measurements with a sufficient accuracy. Since the beginning of the new millennium, space-borne observation techniques based on synthetic aperture radar (SAR) interferometry also have been used to detect ground displacements, i.e., subsidence and uplift, in the Venice coastland. Differential InSAR (DInSAR), first, and interferometric point target analysis (IPTA), at a later stage, have been applied to measure and map displacements occurring since 1992 when SAR data first became available. The capability of SAR interferometry to measure ground vertical movements in large areas at millimetric accuracy has significantly improved the knowledge of the phenomenon. In particular, comprehensive maps of the vertical displacements have revealed the high spatial variability characterizing the ground movements in the Venice region. A general land stability has been detected in the central part of the study area, including the major cities of Venice, Padova and Treviso, with scattered local bowls of subsidence of up to 2-3 mm/year. Conversely, land settlement has appeared as a widespread phenomenon in the northern and southern coast with rates of up to 5 and 15 mm/year, respectively. Uplift rates ranging up to 2 mm/year have been measured in two different large areas located north of Treviso and south of Padova, respectively, whereas higher values are restricted to the eastern sector of the Euganean Hills.