Dike investigations using geophysical methods – techniques for the future?

Abstract

Investigation to provide information about the location and extent of potential mechanically weak and permeable zones of flood defences is a necessity for effective flood defence management. Geophysical techniques are well suited to detect such zones and are themselves non-destructive. An initial investigation can quickly locate problem areas, and a secondary investigation can provide detailed information about the type and extent of the problem. In emergency situations the results of such investigations would allow the optimum location and planning of emergency repair and strengthening works. The investigative techniques can also be employed in post-flood activities to ascertain the extent of damage inflicted during floods, or as part of a long-term flood defence monitoring programme. JOANNEUM RESEARCH has undertaken work to investigate the potential of various geophysical techniques for application in dike investigations. The geophysical techniques have been tested at pilot sites on actual dikes, which concerning the physical characteristic of the hydraulic situation can be divided into two categories: dikes that constantly withhold water (water on one side and air on the other) and dikes that only withhold water in extreme flood situations (air on both sides). Several geophysical techniques were tested and optimised: infrared, ground penetrating radar, and electromagnetic for initial overview investigations; and 2D or 3D geoelectric surveys to provide detailed information in a secondary survey. The results of the geophysical measurements demonstrate that geophysical methods can be successfully employed to investigate dikes, delivering important information about the homogeneity or inhomogeneity of dikes. Particularly, inhomogeneous areas such as leakages and have been detected and validated.