Land subsidence mapping and monitoring through PSInSAR: examples from the Arno river basin (Italy)

Paolo Farina(1) , Paolo Canuti(1) , Nicola Casagli(1) , Alessandro Ferretti(2) , Florian Marks(1) , and Giovanni Menduni(3)

(1) University of Firenze, V. La Pira 4, I-50121, Firenze, Italy
(2) Tele-Rilevamento Europa s.r.l., V. Vittoria Colonna 7, I-20149, Milano, Italy
(3) Autorità di Bacino del Fiume Arno, V. Servi 15, I-50122, Firenze, Italy

Abstract

Spaceborne SAR interferometry (InSAR) has been employed to detect and monitoring ground settlements induced by groundwater extraction over several plain areas located within the Arno river catchment (Italy). This technique enables spatially detailed mapping of ground displacements, thanks to its extensive spatial coverage, good spatial resolution and high accuracy in the deformation measurement. The Permanent Scatterers (PSInSAR) configuration of radar interferometry has been exploited. The use of such a technique over the whole Arno basin territory (9,000 km2), processing data acquired from the ERS1-ERS2 satellites, allowed us to precisely define areas affected by movements, confirming the ground settlement problems already known and well investigated through conventional methods, such as the Prato and the Lucca industrial districts, and detecting ground displacements over areas not still monitored. Results allowed us to detect areas affected by movements, mapping their boundaries and defining a zonation, based on the yearly displacement rates, useful for hazard assessment. These data, combined with an analysis of the elements exposed at risk, their value and vulnerability, have been employed for the production of a subsidence risk map at basin scale. The results of such an analysis have been provided to the Italian public authorities institutionally demanded for hydro-geological risk management. In addition, over specific areas characterized by high subsidence rates an in depth PS analysis based on ERS and Radarsat data, has been carried out. The obtained temporal series of ground settlements, after a validation performed using conventional levelling data, have been compared with piezometric groundwater measurements acquired on several wells since the Seventies. The comparison, showing a strict correlation between water table changes and land subsidence, is helping us to evaluate the cause-effect relations between the two phenomena. Moreover, a stratigraphic reconstruction and a geotechnical analysis of the underground materials, obtained from the available borehole samplings and laboratory tests, have been carried out aimed at obtaining a better understanding of the spatial distribution of ground settlements.

 

Workshop presentation

 

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