During the days between November 11 and 14, 2012 the Umbria region (as well as Tuscany and northern Lazio) was crossed by an intense storm event, coming from the Tyrrenian see, that caused an extreme flood event. Thunderstorm produced an intense rainfall over a greater part of the Umbria region with a duration of 72 hours. The gauge station of Allerona (close to Orvieto town) registered 307 mm of rainfall; the gauge station of Compignano (close to Marsciano Town) 230 mm, while in Ponticelli (Val di Chiana Romana) was measured 252 mm. In Soriano town, province of Grosseto, not so far from the boundaries of the watershed of Paglia-Chiani River, above 360 mm of rainfalls were measured, values statistically similar to values having a return period of 200 years. Rainfalls levels measured in Allerona are similar, for long duration (24-48 hours), to levels of return period of hundred years. The water discharge of Paglia river reached 2.300 m3/s at the cross section of Orvieto Scalo. The resulting flood event has caused considerable damage: the recognition of economic damage amounts approximately to € 230 million. The note describe the effect on the river dynamic due to the flood event and it shows first results of the morpho-sedimentary analysis of Paglia River. In summer 2012 (just before the flood event), the Engineering Geology Group operating within the Dept. of Civil and Environmental Engineering of Univ. Perugia carried out a mophological- sedimentary survey allowing to define exactly the river system conditions and its morfological trend. After the flood event, in december 2012, a high-resolution survey was carried out, using digital aero-photogrammetric tecniques. The photos showed as lots of vegetated bars became nude bars after the removal of the vegetation. It induced a enhancement in river system mobility and a widening of the active riverbed. During the flood event the water occupied the same areas of the river bed in 1954, when the river was characterized by braided morphology. From the digital aerial survey it will be obtained a high resolution DTM after event to be compared to the high resolution DTM we have before event (2008), produced by Lidar data furnished by Basin Authority of Tiber River. Such comparison will allow to evaluate the sedimentary balance related to the recent alluvial floodings (2010-2012).

Analysis of the morpho-sedimentary evolution of River Paglia (River Tiber basin) after an extreme flood event

CENCETTI, Corrado;DE ROSA, PIERLUIGI;FREDDUZZI, ANDREA;TACCONI, Paolo
2013-01-01

Abstract

During the days between November 11 and 14, 2012 the Umbria region (as well as Tuscany and northern Lazio) was crossed by an intense storm event, coming from the Tyrrenian see, that caused an extreme flood event. Thunderstorm produced an intense rainfall over a greater part of the Umbria region with a duration of 72 hours. The gauge station of Allerona (close to Orvieto town) registered 307 mm of rainfall; the gauge station of Compignano (close to Marsciano Town) 230 mm, while in Ponticelli (Val di Chiana Romana) was measured 252 mm. In Soriano town, province of Grosseto, not so far from the boundaries of the watershed of Paglia-Chiani River, above 360 mm of rainfalls were measured, values statistically similar to values having a return period of 200 years. Rainfalls levels measured in Allerona are similar, for long duration (24-48 hours), to levels of return period of hundred years. The water discharge of Paglia river reached 2.300 m3/s at the cross section of Orvieto Scalo. The resulting flood event has caused considerable damage: the recognition of economic damage amounts approximately to € 230 million. The note describe the effect on the river dynamic due to the flood event and it shows first results of the morpho-sedimentary analysis of Paglia River. In summer 2012 (just before the flood event), the Engineering Geology Group operating within the Dept. of Civil and Environmental Engineering of Univ. Perugia carried out a mophological- sedimentary survey allowing to define exactly the river system conditions and its morfological trend. After the flood event, in december 2012, a high-resolution survey was carried out, using digital aero-photogrammetric tecniques. The photos showed as lots of vegetated bars became nude bars after the removal of the vegetation. It induced a enhancement in river system mobility and a widening of the active riverbed. During the flood event the water occupied the same areas of the river bed in 1954, when the river was characterized by braided morphology. From the digital aerial survey it will be obtained a high resolution DTM after event to be compared to the high resolution DTM we have before event (2008), produced by Lidar data furnished by Basin Authority of Tiber River. Such comparison will allow to evaluate the sedimentary balance related to the recent alluvial floodings (2010-2012).
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11391/1169893
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