Page - 678 - in Book of Full Papers - Symposium Hydro Engineering

Fig. 2 Distributed Data - Strain and Temperature - Management and Analysis Software Color coding representation (left) - Point evolution display (right) 2.3. BENEFITS The scale, age and uncertainty of materials in the sometimes huge hydro engineering structures combine a difficult array of parameters for the responsible engineer to navigate when analyzing its structural integrity. Traditional instrumentation based on localized point sensor is not sufficient to guarantee the detection of early signs of damage and localization of unknown events. Distributed fiber optic sensing allows the early detection, localization and sizing of defects and degradations such as seepages, leakages, settlements, shearing, cracks, abnormal joint movements, intentional tampering and over- flooding. 3. INFILTRATION DETECTION FOR DAMS, DIKES AND RESERVOIRS A fiber optic distributed system for infiltration detection relies on Raman distributed thermal sensing and can work in two different configurations; the passive and active methods. The so-called passive method relies on direct detection of temperature anomalies induced by seepage or leak. This method is typically used when a gradient of approximately 5°C between the leaking liquid and the sensing cable can be assured. The so-called Heat Pulse Method or active method is on the other hand used when the gradient between the liquid and the sensing cable is negligible and smaller than 1°C. In order to ensure a reliable detection of the leak, the self- heating cable is heat up and forced to change its natural temperature. Heating is 678