According to the Federal Highways Administration, the most common cause of bridge failure is from floods scouring bed material from around bridge foundations. Scour refers to the physical displacement of sediments due to flowing water, usually around a fixed object. The removal of sediments from around bridge foundations can cause stability problems, and federal regulations require states to inspect all public bridges for scour susceptibility. Scour countermeasures may include bridge replacement, channel “armoring” provisions, and monitoring. One approach to monitoring involves the use of sensors on the bridge that allow DOT&PF staff and others to remotely track actual scour conditions on a near real-time basis. The DOT&PF has 19 bridges with this type of scour monitoring system deployed. These systems are installed, operated, and maintained by the U.S. Geological Survey (USGS) through a cooperative agreement with the DOT&PF.
The USGS currently uses a variety of sensors to track hydrologic conditions and scour depths, including non-contact stage sensors, submersible pressure transducers, acoustical depth sensors,and time-lapsephotography. The data are stored on site and transmitted every four hours via satellite modem. The data are then displayed on a database driven website and are available for download.Both DOT&PF and USGS staff track scour conditions regularly. We have assigned threshold values for scour and receive notification when these threshold values are exceeded. When this happens, the USGS staff make a site visit to verify conditions. For severe scour conditions that pose safety risks, the bridge would be closed to traffic.
Michael Knapp, P.E.
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