Testing ERT and fiber optic techniques at the laboratory scale to monitor river levees

In this paper we present the results of laboratory tests using electrical resistivity tomography (ERT) and fiber optic techniques to monitor river levees. A small-scale levee was constructed with the scale of 1:12 based on the earthen levee of an irrigation canal in San Giacomo delle Segnate, Italy, where a customized ERT monitoring system has been operating since September 2015. The most important mechanisms affecting the stability of river levees were simulated during different tests. To explore the possibility of using fiber optic sensors to monitor the integrity of levee structures, Fiber Bragg Grating (FBG) technology was adopted and four Organic Modified Ceramics (ORMOCER) coated 250μm-diameter fibers were deployed at the water exit side of two leakage zones. ERT data from a miniaturized electrode spread show that changes in the water level in river and the rainfall events significantly affect the resistivity distribution in the levee. Using TDR data, the relationship between water content and resistivity values was calibrated to be able to translate the inverted ERT images into water content maps. The results of fiber optic measurements showed the feasibility of fiber optic sensors to detect the deformations of the levee body in response to water infiltration.