An optical fiber-based monitoring system to study the seepage flow below the landside toe of a river levee

The development of innovative monitoring systems to mitigate the risk associated to river levee failure is a recent challenge involving synergic effort of public institutions, specialized companies and academics. The present study examines a 350 m stretch of Adige river levees, located in the Province of Bolzano (Italy) close to the village of Salorno, interested in the recent past by moderate piping phenomena and subjected to subsequent interventions for seepage control (cut-off diaphragm wall). As is customary, the levee body and its foundation soil were investigated through geophysical and geotechnical surveys. The arising results provided a multi-dimensional characterization of the levee and the nearby soil water-meadows likely to be affected by preferential paths for piping. The detection of those paths entailed the joined use of piezometers and distributed optical fiber sensing (DFOS) system, the latter installed in a shallow trench on the landside. In the last days of October 2018, Northeastern Italy was hit by a tremendous storm and the Adige river was subjected to a relevant double flooding event. This exceptional circumstance, entirely recorded by the monitoring system, gives the chance to provide insight into the seepage process undermining the levee stability.