Implementing a rapid deployment bridge scour monitoring system in Colorado, 2019

The U.S. Geological Survey, in cooperation with the Colorado Department of Transportation, installed and operated real-time scour monitoring instrumentation at two bridges in Colorado in 2016 and 2017 to measure streambed elevations in real-time. The instrumentation included acoustic echosounder depth sensors mounted to the bridge substructure units with rigid conduit and fittings. Although functional, the rigid mounting configuration took several days to install at each site, which limits the instrumentation to long-term deployments at previously determined sites. To address this limitation and allow for greater flexibility in bridge selection, a rapid deployment bridge scour monitoring system (RDBSMS) was developed by the U.S. Geological Survey in cooperation with the Colorado Department of Transportation. The RDBSMSs were installed at two other bridges in Colorado in 2019, which were selected by using specific scoring criteria to rank candidate bridges and the potential for high streamflow based on accumulated snowpack. A matrix was developed to rank candidate bridges based on factors including depth, foundation type, average daily traffic, detour route, and scour critical condition. Colorado Department of Transportation bridges F-05-R and P-01-G were selected as the final candidate bridges for installation and testing of the rapid deploy scour monitoring system.

Bridge F-05-R carries Colorado Highway 13 over the Colorado River near the town of Rifle, Colorado. Because of the misalignment of the pier wall with respect to the river, pier number 4 was instrumented on the left side (looking downstream) to monitor scour conditions. Bridge P-01-G carries U.S. Route 160 over the San Juan River near the Four Corners area in Colorado. Because of misalignment of the pier wall with respect to the river, pier number 4 was instrumented on the right side (looking downstream) to monitor scour conditions. The RDSMSs were installed in approximately 3 hours at each bridge.

Scour conditions at both bridges were monitored during the snowmelt runoff period in 2019 using the installed RDBSMSs. No major scour events occurred at either structure, but minor scour and fill was measured at each. Sensor performance at F-05-R was excellent, with no missing or erroneous data. Sensor performance at P-01-G was good for most of the period, with some missing and erroneous data during periods of high turbidity.

Both RDBSMSs were successfully deployed and produced reliable data, demonstrating that both the technology and the installation methods can work in two different riverine environments. Pre-installation of mounting plates would make the installation process faster at flood prone bridges. Having flood prone bridges preconfigured and several RDBSMSs ready to deploy could allow for rapid monitoring during floods such as those which occurred in 2013.