Investigating the Effects of Water Levels Measured in Two Nearby Rivers on Groundwater Pore Pressures Regime

The paper analyzes the groundwater regime in the embankment foundation of the artificial Gorzone channel located in the Po Plain near Venice, North Italy, under the conditions imposed by the hydraulic regime of the Gorzone itself and the nearby Adige river. Sand boils and blow-outs phenomena occur both at and beyond the levee toe, as the dam located some kilometers downstream is activated to keep the channel water level high for irrigation purposes in spring and summer. In order to design proper interventions, the seepage under the embankment has been investigated and the groundwater regime has been monitored for 2 years. The acquired data revealed that pore pressure regime in the deeper layers is not completely consistent with the Gorzone water level variations; it seems influenced also by the hydraulic regime of the nearby Adige river, that here flows parallel to Gorzone, at the distance of 180 m from the opposite levee. The paper presents the results of some FEM analysis carried out to better investigate the groundwater regime under the influence of Adige and other local forcings. After a calibration based on the acquired pressure data, the model was used to analyze the levee seepage regime under different boundary conditions. The numerical results highlight that the sand-boils and blow outs are probably caused by a seepage confined in the upper high-permeability deposit induced by Gorzone water level, while the deeper pore pressures are mainly related to the Adige hydraulic conditions and to the activity of some extracting wells in the area.