Effect of suspended sediments on ground penetrating radar imaging of riverbeds

Ground penetrating radar (GPR) has proven to be useful for mapping river bedforms, but can also be used to monitor river levels and changing bedforms when in flood and manual measurement may be dangerous. However, there is some uncertainty and lack of clarity on the effects of suspended sediments on the GPR velocity. We present here the results of an experiment to measure the cross-section of the Rakaia River bed during different stages of flow during and after a significant hydrological event. We were able to determine the best fit velocity and scale the GPR travel times to obtain the bedform cross-section remotely. The velocity was about 15 % higher during the highest flow rates, when suspended sediment content was also high. The results are limited but, nonetheless, there is a clear relationship between increasing GPR velocity and increasing suspended sediment concentrations.