The historic church of Santa Croce, dated 5th century AD and located in the city centre of Ravenna (Italy), was originally connected to the Mausoleum of Galla Placidia, contiguous to the Basilica of San Vitale, both Unesco World Heritage sites. A widespread land subsidence process, of both natural and anthropogenic origin, has always affected territories around Ravenna and its city centre, including Santa Croce and the surrounding ruins. This phenomenon has been extensively investigated over the last century. Land settlement, initially of the order of few mm/year, dramatically increased up to 110 mm/year after World War II, primarily due to groundwater pumping and, subordinately, gas production from a number of deep onshore and offshore reservoirs. A significant deterioration to the urban as well as to the natural environments became evident in the late 1970s. In the city centre the crypt of monumental churches, such as S. Francesco’s, and the basement of old buildings were permanently flooded. Cumulative land subsidence nowadays approaches almost 1 m over more than one third of the municipality area including the city and a significant fraction of the coastland, with peaks larger than 1.5 m over a 10 km2 zone located between the historic centre and the coastline. Most recent records, however, show that at present the mainland appears to be substantially stable. In the investigated site of Santa Croce, considering the limited size of the structures in the area and, at the same time, the reduction trend of the phenomenon, subsidence progression does no longer represent a major critical issue. Nonetheless, the cumulative land settlement has reached more than about 3 m with respect to the surrounding areas, well above the typical position of the ground water level, making the site especially sensitive to recurrent flooding, despite continuous dewatering is currently carried out. Main impacts on the investigated site of present conditions, which could be seriously aggravated in the long term by climate change effects (e.g. sea level rise, increased storm surges and changes in precipitation rate), have been identified. First, an increase of flood risk (frequency, severity and duration of inundation) and of rainfall induced floods could make ineffective the drainage systems and/or increase the need for pumping. At the same time, damage to building foundations and subsurface structures could be also generated by progressive loss of functionality of the drainage system, which has been in operation for many decades by now. Within such context, the contribution aims at describing a recent geotechnical investigation campaign carried out to improve the definition of the stratigraphic soil profile and to install a piezometric monitoring system for the control of the shallowest aquifer dynamics. The monitoring system includes not only the Santa Croce site, but also the surrounding San Vitale and Galla Placidia area. The investigation campaign has been carried out in the framework of the EU H2020 SHELTER project, that works towards a heritage-led resilience enhancement of historic areas.
Impact of cumulated land subsidence on the preservation of the Santa Croce historic site in Ravenna, Italy
Michela Marchi;Ilaria Bertolini;Guido Gottardi
2022
Abstract
The historic church of Santa Croce, dated 5th century AD and located in the city centre of Ravenna (Italy), was originally connected to the Mausoleum of Galla Placidia, contiguous to the Basilica of San Vitale, both Unesco World Heritage sites. A widespread land subsidence process, of both natural and anthropogenic origin, has always affected territories around Ravenna and its city centre, including Santa Croce and the surrounding ruins. This phenomenon has been extensively investigated over the last century. Land settlement, initially of the order of few mm/year, dramatically increased up to 110 mm/year after World War II, primarily due to groundwater pumping and, subordinately, gas production from a number of deep onshore and offshore reservoirs. A significant deterioration to the urban as well as to the natural environments became evident in the late 1970s. In the city centre the crypt of monumental churches, such as S. Francesco’s, and the basement of old buildings were permanently flooded. Cumulative land subsidence nowadays approaches almost 1 m over more than one third of the municipality area including the city and a significant fraction of the coastland, with peaks larger than 1.5 m over a 10 km2 zone located between the historic centre and the coastline. Most recent records, however, show that at present the mainland appears to be substantially stable. In the investigated site of Santa Croce, considering the limited size of the structures in the area and, at the same time, the reduction trend of the phenomenon, subsidence progression does no longer represent a major critical issue. Nonetheless, the cumulative land settlement has reached more than about 3 m with respect to the surrounding areas, well above the typical position of the ground water level, making the site especially sensitive to recurrent flooding, despite continuous dewatering is currently carried out. Main impacts on the investigated site of present conditions, which could be seriously aggravated in the long term by climate change effects (e.g. sea level rise, increased storm surges and changes in precipitation rate), have been identified. First, an increase of flood risk (frequency, severity and duration of inundation) and of rainfall induced floods could make ineffective the drainage systems and/or increase the need for pumping. At the same time, damage to building foundations and subsurface structures could be also generated by progressive loss of functionality of the drainage system, which has been in operation for many decades by now. Within such context, the contribution aims at describing a recent geotechnical investigation campaign carried out to improve the definition of the stratigraphic soil profile and to install a piezometric monitoring system for the control of the shallowest aquifer dynamics. The monitoring system includes not only the Santa Croce site, but also the surrounding San Vitale and Galla Placidia area. The investigation campaign has been carried out in the framework of the EU H2020 SHELTER project, that works towards a heritage-led resilience enhancement of historic areas.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
