GNGTS 2018 - 37° Convegno Nazionale

702 GNGTS 2018 S essione 3.2 mechanism is involved. Such a kind of correlation has been already observed in the central part of the Po Delta, in particular in Taglio di Po and Porto Tolle areas (Vitagliano et al. , 2017). As expected, the analyses of the time evolution of the mean annual and annual cumulative values have shown some correlations among hydrometric level, rainfall and groundwater levels. In particular, the relative Po di Goro river level measured at Ariano SIAP station, reaches maximum mean annual value in 2009-2010 and 2013-2014, while lower values during 2011- 2012 and 2015-2017 (Fig. 2a). The mean annual cumulative rainfalls measured at Goro station show maximum values in 2009-2010 and 2014-2017 and lower values in 2011-2013 (Fig. 2b). The groundwater levels of the shallower unconfined aquifer and the floating porous lens depend by both water river and rainfalls. In fact, Piezometer 134 (Fig. 2c), which is close to the Po di Goro, better correlates with the river hydrometric level (Fig. 2a), while Piezometer FE23 (Fig. 2d), close to Po di Volano river, shows higher similarities with the local rainfalls (Fig. 2b). The former piezometer exhibits a groundwater level that reaches minimum depth in 2012 and a depth-decreasing from 2015 to 2017, while the latter piezometer shows lower groundwater levels only in 2012-2013. Modelling and discussion. Our analyses aim to identify the most reliable physically-based modelling for simulating the periodic components and estimating the geodetic trend from residual ground displacement. In particular, useful information have been derived from the piezometric data. FE23, located near Codigoro area, shows annual groundwater fluctuations within the soil sequence (up to 3 m below the ground level, b.g.l.) that better correlate with the local rainfall at Goro station (Figs. 2b and 2d). Conversely, the piezometer located close to the Po di Goro River (Ariano del Polesine 134) exhibits groundwater annual values that mainly correlate with the river stage (Figs. 2a and 2c). Thus, the infiltration of rainwater in the soil sequence seems to be more active far from the river. Since the GPS antenna is far from Po and Po di Goro Rivers, and it is fixed to a building characterised by shallow foundations (up to 2 m b.g.l.), it may be heavily influenced by water infiltration processes, as it occurs in FE23 site. Its oscillations may be due to the hydrological loading depending on rainfall, soil moisture Fig. 2 - Mean annual values histograms of: (a) hydrometric level of Po di Goro River; (b) cumulative rainfall at Goro station; (c) and (d) piezometric levels at Ariano del Polesine 134 and FE23, respectively.