Detection of woody roots growing in earth dikes using geophysical investigations

Detection of woody roots growing in earth dikes using geophysical investigations 

The Mediterranean Basin is prone to a plethora of natural hazards among which floods. Hydraulic structures are built to mitigate flood risk on population and assets. This risk is particularly crucial in the French Mediterranean region where about 2000 km of dikes only on PACA region, protect a large population. Roots are recognized as an environmental hazard when growing in hydraulic earth structures such as flood protecting or channel levees and dams. The aim of this thesis is to better assess how woody vegetation compromises levee integrity. To this end, we have to design a methodology including non-destructive methods and geophysical models in order to detect and localize woody roots growing in earth dikes. Trees’ rooting in earth dikes generates two types of risks: internal erosion due to root development in earth embankments, and external erosion (slopes and crest) which is often related to trees uprooting. In order to characterize the consequences of woody root systems on the structure and durability of dike embankments, it is necessary to define dangerous roots position in the embankment. Several geophysical methods are often used for exploration, detection and3D tomography of soil. Among them, some have been developed for tree roots detection such as electric – electromagnetic or acoustic prospection. Nevertheless, given the complex variety of bank and soil properties composing earth dikes, these non destructive methods and the models associated have to be adapted and improved to detect and localize woody roots in these specific conditions.