Upgrade of the G.Re.T.A. system installed on the Parma River

Upgrade of the G.Re.T.A. system installed on the Parma River

Politecnico di Milano University, AIPO and LSI LASTEM

At the end of December 2020LSI LASTEM has been granted significant technological upgrade of one of the first G.Re.T.A. (Geo Resistivimeter for Time-lapse Analysis) systems installed on the embankment of the Parma River in Colorno, in the reclamation area of the Interregional Agency for the PO River (AIPO). 

Collaboration with the Politecnico di Milano and with AIPO 

LSI LASTEM has been collaborating with Politecnico di Milano for over 6 years for the prediction and prevention of hydrological risk in the context of levees monitoring. Geoelectric monitoring has proven to be a winning technology for recognizing in advance not homogenous seepages in the embankmentspiping phenomena, and the creation of cavities. 

During the Fondazione Cariplo “Tech Levee Watch” project and subsequently in the “Dilemma” project of  the Ministero dell’Ambiente e della Tutela del Territorio e del Mare, LSI LASTEM designed and installed the geo-resistivity meter for fixed installations in critical embankmentsnamed G.Re.TA. 

The monitored site is in Colorno, in the province of Parma, with a 94 m embankment monitoring span of the Parma river which has been kept under control since December 2018. 

Colorno: the flood of 2017 

On 12th of December 2017 the city of Colorno was hit by a disastrous flood caused by the Parma Riverwhich caused the flooding of the courtyard of the Royal Palace and the respective park, the main square and the historic center of the town. The flood event had also damaged the embankments of the River in two sites, due to piping phenomena that had caused water to leak on the countryside side, with the flooding of nearby houses. 

The embankments of the Parma River were subsequently analyzed with geophysical techniques to evaluate the internal structure of the levees. One of the two sites damaged during the flood was chosen for the installation of the G.Re.T.A. system.

What does the G.Re.T.A. system do? 

G.Re.T.Ais the most effective and innovative solution for permanent geoelectric monitoring of the conditions of large sections of the subsoil. The instrument remotely measures the alterations over time of the resistivity profile of the soilfunctional to the characterization in terms of water contentpresence of cavities or other anomalies. The system sends the data to a cloud software where they are automatically processed and where it is possible to set alarm thresholds,  after which alert messages are automatically sent. 

Electrical Resistivity Tomography (ERT), on which the system is based, is an effective technology for analyzing the structural integrity of earth embankments, as it allows, in a non-invasive way, to underline non-homogeneities and, thanks to the monitoring, to show changes in soil properties over time.

System upgrade: how has monitoring been improved? 

At the end of December  2020 a technological upgrade of the monitoring station was carried out, to adapt it to all the  technical improvements made by LSI LASTEM in the last two years. 

Among them, an improvement in the algorithm and in the current injection sequence made the measurements more stable, the maximum injectable current was doubled to allow obtaining high quality resistivity values even in depth. 

The connectivity of the system was enhanced to guarantee a stable connection of the instrument to the cloud and the possibility of reaching the station remotely for maintenance. 

With the adaptation of the system to the most modern release, the monitoring of the Parma River embankment continues to be an important help to prevent instability and to ensure effective operation of the structure in a site with a high hydrogeological risk. 

Valeria Menichini

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