A Simple New Georadar Survey Method For Bathymetric Profiling Over White Water Rapids

A major hydroelectric project of Hydro-Québec (Rupert River Diversion) required geophysical investigations at the location of future sites where weirs and cofferdams will be constructed. The<br>engineers required accurate information of the rock profile and the bathymetry for adequate designs. These data were not accessible from conventional geotechnical and geophysical investigations methods in dangerous river rapids. An innovative bathymetric method, using the georadar technology was then set up and successfully used by Geophysics GPR International.<br>A SIR 3000 system (from GSSI) was used for its lightness and energy autonomy. The use of the 1.5 GHz antenna was dedicated to the water surface topography measurements, which were necessary for the accurate seismic refraction calculations, as well as for the aerial georadar bathymetric surveys. A 270 MHz antenna was suspended to a steel cable crossing the river, for the bathymetric measurements. Both antennas were located in 3D with a dynamic laser total station, and all the further calculations used the three information sources together to correctly extract the accurate water surface topography as well as the first bathymetric estimation. A special methodology was finally applied to correct the raw bathymetric results, taking into account the effect of the white water effects.