An evaluation of scour measurement devices

Scour, the leading cause of bridge failures, affects hundreds of thousand bridges and costs hundreds of millions of dollars in direct repair costs in the U.S. alone. Furthermore, scouring has also been linked to catastrophic failures that resulted in the loss of human lives. The U.S. Federal Highway Administration has proposed several countermeasures to reduce the impact of bed degradation. One of these countermeasures that is particularly relevant during peak flow periods is the real-time monitoring. Two common scour monitoring techniques are the sonar fathometers and time domain reflectometry. A novel vibration-based monitoring technique, which exploits the nature of turbulence in open channel flows for measuring scour hole depth has recently been proposed.Through an extensive experimental campaign, the authors evaluate the dependency of the performance of these three monitoring techniques on the channel conditions, such as the water temperature, and salinity or sediment concentration. The experimental results indicate that both the time domain reflectometry and sonar methods are sensitive to the channel temperature and salinity. For the sonar device, such effects can be accounted for by modifying the speed of sound for different temperature and salinity levels. For the time domain reflectometry method, the temperature effects can be accounted for using the above approach, while the presence of salinity degrades the waveform features limiting the device to non-saline environments. Salinity and temperature are shown to have little effect on the novel method. Furthermore, the time domain reflectometry and vibration-based methods are observed to be insensitive to suspended sediment concentrations and turbid flow. Sonar, however, is shown to be sensitive to moving turbid water. In varying topography, sonar is found to record the minimum depth within the beam diameter. Flow misalignments up to 90° have little impact on the vibration-based method.