Talsperre Dornau - flächige Überwachung mittels faseroptischem Retrofitsystem

Dornau dam is situated along Lech River. A secondary downstream reservoir causes impounding of the embankment on the downstream side. In recent years, observations that could imply leakage through the dam were made. Since direct leakage measurements at the dam toe are not possible due to the upstream impounding, it was decided to install a fibre-optic monitoring system through retrofit installation of hybrid fibre optic cables. Leakage monitoring is based on distributed temperature sensing of the internal dam temperature. From the dam crest, 21 boreholes were drilled to depths of 3,5 m below dam base. Cable loops were installed in the boreholes before they were grouted. The individual cable segments were connected to form two measurement loops spanning the entire length of the dam. Temperature gradients are continuously monitored to assess leakage. Operators are informed through an automated alarm evaluation if temperature gradient thresholds are exceeded. Heat-pulse measurements can also be performed to complement gradient measurements. After one year of operation, the monitoring system has proven to provide a reliable data acquisition with high-quality measurements. No indications for leakage are currently present, however will be identified at an early stage in the future if the situation should change.