Two geophysical methods used for determining the cause of water leakage through sealing walls

During the last five years a run-of-river-scheme hydropowerplant was built at the river Danube by Verbund Company, the largest supplier of electrical energy in Austria. The mainbuilding (weir, locks and powerhouse) is situated near the southern boundary of Vienna, the capitalof Austria. The backwater area extends 30 km up the river through the heart of the city. Because of different reasons there had to be built a system of cut-off walls on the right riverbank. These cut-off walls had to obey very restrict quality orders. While filling the reservoir the accompanying groundwater had been observed by an extensive set of monitoring wells. Shortly after the static water level was made the monitoring showed abnormal heights of the groundwater behind the sealing walls at a few locations. Judging the question of liability only two reasons for this behaviour are important: flow through the sealing wall or under the sealing. Besides inspecting the engineering, hydrological and geological facts two geophysical methods were used for the detection of the cause of leakage. These methods were the ECR™method and a thermometrical method.