Monitoring the foundation soil of an existing levee using distributed temperature fiber optic sensors

Increasing reliability of levees is one of the main strategies to follow for flood risk reduction. Through monitoring it is possible to assess the response of levees to floods and to identify areas that may be subject to sand boiling. In this work a new monitoring system based on distributed temperature fiber optic sensors is presented. A hybrid cable that embeds optical fibers and electric wires has been installed at the toe of a 350 m long stretch of an operational levee in Northern Italy along with traditional sensors such as piezometers and spot temperature sensors. Through the interrogation of the fiber it is possible to acquire temperature measures every 1 m with an accuracy of 0.5 °C. Besides, by heating the cable through the electrical wires, the transient behavior in response to the active heating and consequent passive cooling along the fiber is assessed. Since heat is mostly transferred by advection, this procedure enables to estimate the presence of groundwater flow in different zones along the levee stretch. First results show a good correspondence between areas with larger presence of sandy levels and the fiber data. Further developments will arise when a significant flood event will provide an intense seepage driving force within the levee foundation to be detected by the sensors.