Combined GNSS, EGMS and Veneto Region InSAR datasets for the monitoring of Land Subsidence in the Po River Delta (Italy)

The PO River (POR) with an enlargement of 400 km2 and complex ecosystem is in North-East Italy, where the PO River flows into the Adriatic Sea. It related to natural sedimentary processes due to human activities, such as filling the wetland area and engineering attempts. The gradual or sudden sinking or lowering of the earth`s surface is called land subsidence. Land subsidence can have different natural drivers such as temporal variability of sediment compaction, tectonic, but it can be also anthropic such as exploitation of underground water, mining (extraction of oil, gas and so on). Subsidence in the PO River Delta is due to both natural and anthropogenic causes. The natural part is highly connected with the age of the soft easily compressible sediments of the Holocene age that form the 30-40 meters of the topsoil layers. With time, these young deposits which are poorly compacted settle and compact elastically, going a long way toward accounting for the current ground subsidence in the area. This natural compression, aside from other human influences, contributes to the land subsiding little by little. The anthropogenic component is linked to the extensive exploitation of non-confined, sime-confined, and confined aquifers. Hosting some 3 million people in this area, huge quantities of water are used not only for daily uses but industrially and agriculturally, in public perspective. In fact, above 60% of it is constituted by over 100,000 wells whose depths range from 10 to 700 meters. The majority of these wells are located in the Apennine foothills and draw from unconfined, semi-confined, and confined types of aquifers. The foothill areas can also be considered part of alluvial fans created by rivers coming down from the Apennines, distributing sediments and water across the landscape. These are very high extractions of wells that putting great stress on the groundwater system, influencing water availability and land stability. Land subsidence exists around the world, and due to this phenomenon, the risk of flooding increases in transitional environments such as river delta which often marked with dense populations and extensive economic activities. Long term subsidence can cause ground surface cracking, infrastructure destruction, saltwater intrusion, salinization and so on. The coastal area around the world is experiencing unprecedented changes due to climate changes, the most significant among them is the raising see level. The consequence of land subsidence depends on the coastline and surface changes, services interruptions, buildings damage, salinization and flooding of large areas. Therefore, It is worth mentioning that dealing with the land subsidence issues should be a priority not only for public's wellbeing but also for promoting sustainable development, especially in the delicate areas of the coastal zone where the earth is vulnerable to catastrophic shifts. In the past, monitoring of ground deformation has been the task of traditional techniques like leveling, total station and/or GNSS methods. These techniques are well known for their precision but bear a serious disadvantage in the form of being reliant on a limited number of observational points making large area coverage very difficult to achieve, if at all. To avoid these spatial constraints, InSAR technology has emerged as a great tool for wide area ground deformation monitoring. This technique provides a more effective method for land deformation assessment over greater space allowing for traditional techniques shortcomings. The InSAR data of this work were represented by European Ground Motion Service-EGMS and Veneto Region InSAR Data while different GNSS observations included three continuous GNSS-CGNSS stations, namely TGPO, PTO1, and CODI, together with 46 other NPS GNSS. Comparing, calibrating, and validation of such satellite- and ground-based datasets constituted a wholly integrated monitoring system for the studied area.