The urban area of Ferrara is developed in a low-lying region, subject to significant pollution, flooding and seismic risks. The town has grew at the junction of the Po delta area, the alluvial meander plain of the Po river, and the alluvial systems fed by Apennines-derived streams. The sedimentary evolution of the river systems strongly influenced the urban shape, but human intervention in turn changed the fluvial dynamics, to generate the present-day artificial state. Near the divergence point of these channels, Ferrara was founded during the early Middle Ages (7th century), as a fortified structure, built on a crevasse splay, part of the natural levee body of the Po, near the border between Byzantine and Lonbardic influence area. The southern side of the fortified village, was about 240 m long, its area 35,000 squared metres. The proto-urban structure then grew in a linear way, on the sandy levee crest, since the topographically elevated structure offered protection against flooding waters and provided comparatively firm and well drained ground. During the first half of the 11th century, the urbanised area on the northern levee of the Po stretched over a distance of about 2300 m, with an average width of 50-100 m During Medieval times, also the southern levee of the Po was overbuilt. At the beginning of the 12th century, the modern Po channel, flowing at the north of the town, was generated, during a river reorganisation phase. During the following centuries, the early pattern of urban tissue growth through individual building cell implantation gave way to discrete episodes of town planning and urban expansion, associated with land reclamation works and water canalization. These extensive works made the urban expansion into interfluvial depressions possible. At the ending of the 15th century, a large renaissance expansion (Addizione Erculea) into argillaceous depression took place. During the following century, the water flow in the southern Po channels was terminated by an ill-fated attempt to force the Reno River into reaching the sea through the former Po di Primaro delta mouth. The very low topographic gradients and the elevated sediment load transported by this Apennines-derived river rapidly silted up the ancient Po di Ferrara channel, just at the west of the town. Large marsh therefore developed in the areas surrounding the town, engulfing large southern suburbs. After a long period of stagnation, the urban growth took a significant pace only after WWII, in ways totally unaware of the historical, geological and environmental constrains and thus producing significant hazard levels. The Po, Panaro and Reno river water levels are mach higher than the topographic elevation of the town, generating a major flooding risk. The subsurface waters also largely affect the building degradation state. In a anti-intuitive way, impregnation levels are much higher above permeable fluvial sand bodies, showing lower phreatic water levels, than on organic rich argillaceous interfluvial deposits, characterized by higher phreatic levels. The stratigraphic architecture also influence the geotechnic and seismic response property, bothic in the historic city and in the modern suburbs.

URBAN GEOLOGY, HISTORIC DEVELOPMENT AND PRESENT-DAY MANAGEMENT OF THE TOWN OF FERRARA.

STEFANI, Marco;ZUPPIROLI, Marco
2012

Abstract

The urban area of Ferrara is developed in a low-lying region, subject to significant pollution, flooding and seismic risks. The town has grew at the junction of the Po delta area, the alluvial meander plain of the Po river, and the alluvial systems fed by Apennines-derived streams. The sedimentary evolution of the river systems strongly influenced the urban shape, but human intervention in turn changed the fluvial dynamics, to generate the present-day artificial state. Near the divergence point of these channels, Ferrara was founded during the early Middle Ages (7th century), as a fortified structure, built on a crevasse splay, part of the natural levee body of the Po, near the border between Byzantine and Lonbardic influence area. The southern side of the fortified village, was about 240 m long, its area 35,000 squared metres. The proto-urban structure then grew in a linear way, on the sandy levee crest, since the topographically elevated structure offered protection against flooding waters and provided comparatively firm and well drained ground. During the first half of the 11th century, the urbanised area on the northern levee of the Po stretched over a distance of about 2300 m, with an average width of 50-100 m During Medieval times, also the southern levee of the Po was overbuilt. At the beginning of the 12th century, the modern Po channel, flowing at the north of the town, was generated, during a river reorganisation phase. During the following centuries, the early pattern of urban tissue growth through individual building cell implantation gave way to discrete episodes of town planning and urban expansion, associated with land reclamation works and water canalization. These extensive works made the urban expansion into interfluvial depressions possible. At the ending of the 15th century, a large renaissance expansion (Addizione Erculea) into argillaceous depression took place. During the following century, the water flow in the southern Po channels was terminated by an ill-fated attempt to force the Reno River into reaching the sea through the former Po di Primaro delta mouth. The very low topographic gradients and the elevated sediment load transported by this Apennines-derived river rapidly silted up the ancient Po di Ferrara channel, just at the west of the town. Large marsh therefore developed in the areas surrounding the town, engulfing large southern suburbs. After a long period of stagnation, the urban growth took a significant pace only after WWII, in ways totally unaware of the historical, geological and environmental constrains and thus producing significant hazard levels. The Po, Panaro and Reno river water levels are mach higher than the topographic elevation of the town, generating a major flooding risk. The subsurface waters also largely affect the building degradation state. In a anti-intuitive way, impregnation levels are much higher above permeable fluvial sand bodies, showing lower phreatic water levels, than on organic rich argillaceous interfluvial deposits, characterized by higher phreatic levels. The stratigraphic architecture also influence the geotechnic and seismic response property, bothic in the historic city and in the modern suburbs.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11392/2289036
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