Ground displacement data around the city of Ravenna do not support uplifting Venice by water injection

Abstract

The proposed injection of seawater in a brackish, sandy aquifer\ud lying 600–800 m under the lagoon of Venice to lift Venice itself\ud uniformly up to 30 cm in 10 years raises many problems. We\ud discuss here whether a smooth uplift can be obtained as\ud claimed by the proponents. We first underline the similarities\ud between the Ravenna and Venice case. We then examine the\ud subsidence around Ravenna because of fluid extraction and the\ud measured surface displacements for the period when there is\ud pressure recovery both in the depleted gas reservoir close to\ud Ravenna and in the upper aquifer system. Uniform surface\ud settlements are nowhere observed and strong influence of local\ud heterogeneities cannot be ruled out. The whole picture suggests\ud great caution and the need for much more investigation\ud before undertaking such an injection

Estimation of Subsidence in Po Delta Area (Northern Italy) by Integration of GPS Data, High-Precision Leveling and Archival Orthometric Elevations

“…Natural subsi-dence has been estimated at 1 -2 mm/year in the Delta. Reclamation has also caused local subsidence, but cannot completely explain the falling rates over the last 60 years [38]- [44].…”

“…Due to the significant economic impact of subsidence, vertical movements have been monitored since 1950 [45] by repeated high-precision leveling, undertaken by the IGMI (Istituto Geografico Militare Italiano) and later by other local authorities, companies and institutions [22] [39] [44] [46]- [49]. Caputo et al [39] and Borgia et al [47] reported a maximum subsidence rate of 250 mm/year in the central part of the Po Delta for the period 1951-1957 and 180 mm/year between 1958 and 1962.…”

“…The GPS technique has more recently been used to integrate conventional leveling with episodic and continuous measurements on spirit leveling lines [50]. Recent studies have shown that subsidence, although reduced, is still ongoing [44] [51]- [54]. Most of the Po Delta area now lies below sea level, sometimes by as much as 6 -8 meters, and subject to flooding of river branches and other water courses.…”

On the uniformity of anthropogenic Venice uplift

“…Recently, some concerns on the uniformity of the predicted uplift have been raised (Schrefler et al. , 2009) by comparison with the land settlement experienced at Ravenna, a town 120 km south of Venice, where extensive joint gas and groundwater withdrawals have caused a large non‐uniform subsidence during the 1970s.…”

Flood Protection in Venice under Conditions of Sea-Level Rise: An Analysis of Institutional and Technical Measures

“…According to Comerlati et al (2004) this solution might raise the city of Venice by 25-30 cm in 10 years. However, the level of risk of major damage to city structure and buildings due to uneven land uplifting is matter of scientific debate (see for example, Gambolati 2009;Schrefler et al 2009). …”