Abstract: Tropical Storm Irene swept through Vermont with 100-200 mm (4-8 inches) of rain, causing intensive flooding in the Southern and Central regions. Over 300 bridges suffered damage or failed as a result of heavy rains. Resources from the Vermont Agency of Transportation, Vermont Agency of Natural Resources, and Vermont Regional Planning Commission were joined to create a comprehensive bridge database. The database combines the stream characteristics and Irene damage along with the bridge attributes into a common resource that can be used for analysis. The examination of affected bridges showed scour as the dominant mode of damage from Irene. Bridges damaged tended to have floodplain contraction, and spans incapable of passing flood flows. Flow constriction and floodplain blockage were key indications of poor performance.
Abstract: This paper presents a methodology on prioritizing deployment of scour sensors at high-risk bridges using a holistic approach. Specifically, stream geomorphic data, bridge design information, and bridge scour ratings are used to intelligently identify and prioritize bridge sites for remote scour monitoring. Scour is the leading cause of bridge failure, with 309 bridges in the State of Vermont rated as scour critical. Using Vermont as a case study, this work looks to correlate bridge structural design data with hydraulic and stream geomorphic information to identify bridges at high risk of scour processes, and specifically for bridges more structurally susceptible to scour damage. Including additional stream and hydraulic indicators in the analysis, rather than relying on structural evaluations alone, enables areas of geomorphic instability to be identified; and bridges in these areas can be outfitted with scour monitoring devices. Lowcost monitoring devices are proposed to monitor at-risk bridges and to provide additional information in scour-prone areas. A sensor under development would allow for direct installment into stream beds at existing bridges, and incorporate accelerometer-based monitoring, with wireless data transmission. The device would allow for real-time measurement of streambed degradation and aggradation during high flow events, thereby providing timely information regarding critical scour events. This work aims to aid State transportation engineers in identifying, which bridges in the transportation network are at risk, of scour processes, provides useful insight into scour rating systems, and assesses the value of the geomorphic assessments to improve our existing bridge rating system. The compilation of results from geomorphic assessments, scour ratings, and bridge design information will be presented.
Abstract: Scour is the leading cause of bridge failure throughout the United States and elsewhere. Reliable scour ratings and methods for estimating the potential for scour can be effective tools in predicting and mitigating scour damage to bridges. The Vermont Agency of Transportation (VTrans) rates every bridge in the state for susceptibility to scour-type failure following the Federal Highway Administration's National Bridge Inventory guidelines. The scour rating is largely bridge and site specific and currently does not account for larger-scale stream geomorphic characteristics. In a complementary effort, the Vermont Agency of Natural Resources (VTANR) performs detailed geomorphic assessments of streams and rivers; more than 2,000 stream miles have already been assessed. This additional stream geomorphic data could prove to be useful in the scour assessment of bridges. This paper uses VTANR's geomorphic observations made around bridges and VTrans' scour ratings to explore preliminary correlations for assessment of scour potential of Vermont bridges.