Bridge Scour in Montana

Science Center Objects

Bridge scour is the erosion of streambed material away from pier foundations and abutments and is the leading cause of bridge failure in the United States (Richardson and Davis, 2001). Since the early 1990s, the U.S. Geological Survey (USGS) and the Montana Department of Transportation (MDT) have had a cooperative bridge scour project in Montana.

Project tasks included collection of bridge scour data, evaluation and development of scour and channel-stability assessment methods, monitoring scour at selected bridges, and the assessment of scour and channel stability at bridges in Montana. These efforts have resulted in the identification of bridges that may be susceptible to substantial scour during large floods. A Plan of Action (POA) has been developed by MDT for each bridge to comply with federal requirements. The POA establishes that monitoring will be conducted to assess scour conditions, and includes the monitoring of scour countermeasures that have been constructed at certain bridges to resist scour (Lagasse and others, 2009). The purpose of monitoring is to determine if scour and channel instability are taking place in the vicinity of a bridge. Monitoring may be used in the interim pending installation of physical countermeasures; instead of physical countermeasures; or with physical scour countermeasures to monitor bridge and channel instability over time. Monitoring can include portable, fixed, and visual methods (Hunt, 2009) and may be conducted continuously or intermittently before, during, and after high-runoff conditions. Bridges that do not have physical countermeasures in place typically are monitored during high-flow periods. Monitoring has been conducted by the USGS in Montana to assess the integrity of installed scour countermeasures subjected to high-flow conditions (Holnbeck and McCarthy, 2010).

Objectives:

  • Conduct scour monitoring at selected bridges in Montana,
  • Collect additional scour and hydraulic data to facilitate better understanding and prediction of scour processes to protect public safety, and
  • Investigate new methods and technology to measure scour and collect hydraulic data more effectively.