ASSESSMENT OF BRIDGE PIER SCOUR USING IMPULSE RADAR

This Paper describes, and illustrates, the use of impulse sub-surface radar in detecting the presence of scour holes in river beds. The basic theory of radar signal emission is briefly described to show the theoretical limits of a system. This is followed by a review of surveys carried out in lakes and rivers, with the values of the Limits actually attained. The accuracy of any system is dependent on an accurate knowledge of the values of the medium electrical properties. An effective laboratory method of evaluating the electrical properties of a material is to incorporate it into a coaxial transmission line and to use a network analyser to take reflection and transmission impedance measurements over the range of frequencies that are of interest. Transmission line equipment developed at Liverpool University to measure the electrical properties of river water, mud and silt suspensions is described. The variation of these properties along the length of a river is shown for River Dee water and silt samples. Computer modelling of radar signals has also been developed, and the results obtained are compared with signals measured at both Liverpool University swimming pool and a small-scale model of a scour hole. Finally, the held results obtained during on-site testing on the River Severn at Gloucester are presented.