Bridge Scour Countermeasures

Science Center Objects

Flood events on rivers can cause erosion of the soil around a bridge foundation. This process is frequently referred to as bridge scour. Over time, scour can lead to bridge failure. To manage the risk from bridge scour, countermeasures are now used on bridge foundations. USGS scientists will be evaluating these bridge scour countermeasures at bridges across the country on rivers of various sizes.

Bridge scour, or the process of erosion around a bridge foundation caused by flooding, is the leading cause of bridge failure. Bridge scour countermeasures can be used to mitigate the scour effects. We will be evaluating bridge scour countermeasure performance at small, medium, and large bridges in various watersheds throughout the country.

Bridges will be surveyed using these methods

Missouri Water Science Center boat equipped with terrestrial lidar and multibeam echo sounder
  • Multi-beam bathymetry
  • Terrestrial LiDAR
  • Side-scan sonar
  • single-beam bathymetry
  • Underwater camera
  • probing inspection
  • total station
  • GPS
  • pebble count
  • wading survey

From a preliminary list of approximately 120 bridges across the nation that will be categorized by the Federal Highway Administration as “Coastal”, “Large”, “Medium” and “Small”, the bridge will be weighted against several factors.

Factors used to weight the bridge list

  • Does the site have USGS streamflow-gaging stations within the basin to assess flood history?
  • Can previous scour studies be cross referenced?
  • Does the site meet optimal site conditions and water depth?
  • Is the site close to other sites to improve efficiency?  

Once the site list is narrowed down, sites will be grouped based on methodology to be used which is chosen by site condition and water depth. We will work with FHWA personnel to develop general processes and a template format for the scour-countermeasure evaluations. Bridges within each of the 4 FHWA categories (Coastal, Large, Medium, and Small) will be assessed using one or more of the methods above. Individual site assessments will collect provisional data and follow a generalized “template” approach to ensure consistency and that data-collection activities meet the project objectives.

Data being collected during bridge assessments

River bathymetry combined with LiDAR from bridge scour countermeasure evaluation
Terrestrial LiDAR and river bathymetry data combined for bridge scour countermeasures evaluation.
  • Basic countermeasure-assessment data: general site and scour assessment including site sketches, stream classification, and other descriptions.
  • Reference Marks.
  • Flood-frequency/flood history analysis: site must either have USGS gage (10-years of record), nearby gage that correlates (QPPQ method, etc.), or an existing set of applicable regression equations.
  • Compilation of FHWA / State DOT site information and plans at all sites.
  • Description of adjacent overflow bridges, corrugated metal pipe or pipe-arch culverts (squash pipes)
  • Description of bridge superstructure

Once data collection at a site is complete, the evaluation template will be filled out with the following

  • Compiled data from the local transportation authorities (as available)
  • USGS streamflow information
  • Qualitative site data/information: basic countermeasure-assessment data
  • Quantitative site data: descriptive characteristics of scour countermeasures (rip rap dimension, orientation, and so forth) and applicable metadata for all spatial data

Information from the evaluation templates will allow us and FHWA to easily review, interpret, and assess the data from each site before final publication.