[Paper Review] An evaluation of empirical equations for assessing local scour around bridge piers using global sensitivity analysis

G. Gavriel, Maria Pregnolato+3 more|arXiv (Cornell University)|Jan 12, 2026

Hydrology and Sediment Transport Processes0 citations

TL;DR

The paper assesses eight empirical pier-scour equations against the USGS field and lab data, applying both one-at-a-time and global sensitivity analyses to identify influential parameters and determine which equations perform best under field conditions.

ABSTRACT

Bridge scour is a complex phenomenon combining hydrological, geotechnical and structural processes. Bridge scour is the leading cause of bridge collapse, which can bring catastrophic consequences including the loss of life. Estimating scour on bridges is an important task for engineers assessing bridge system performance. Overestimation of scour depths during design may lead to excess spendings on construction whereas underestimation can lead to the collapse of a bridge. Many empirical equations have been developed over the years to assess scour depth at bridge piers. These equations have only been calibrated with laboratory data or very few field data. This paper compares eight equations including the UK CIRIA C742 approach to establish their accuracy using the open access USGS pier-scour database for both field and laboratory conditions. A one-at-the-time sensitivity assessment and a global sensitivity analysis were then applied to identify the most significant parameters in the eight scour equations. The paper shows that using a global approach, i.e. one where all parameters are varied simultaneously, provides more insights than a traditional one-at-the-time approach. The main findings are that the CIRIA and Froehlich equations are the most accurate equations for field conditions, and that angle of attack, pier shape and the approach flow depth are the most influential parameters. Efforts to reduce uncertainty of these three parameters would maximise increase of scour estimate precision.

Motivation & Objective

• Assess eight empirical equations for local scour around bridge piers against open USGS data from field and laboratory conditions.
• Apply one-at-a-time and global sensitivity analyses to compare parameter influence.
• Identify most accurate equations under field conditions and key parameters driving uncertainty.

Proposed method

• Compare eight empirical scour equations, including the UK CIRIA C742 approach, against the USGS pier-scour database.
• Perform one-at-a-time sensitivity analysis to rank parameter importance.
• Apply global sensitivity analysis to vary all parameters simultaneously and assess overall influence on scour estimates.
• Identify which parameters (e.g., angle of attack, pier shape, approach flow depth) most affect predictions.
• Evaluate accuracy of equations under field vs. laboratory conditions.

Experimental results

Research questions

• RQ1 Which empirical scour equations most accurately predict local scour depths in field (USGS) data?
• RQ2 How do parameter sensitivities differ between one-at-a-time and global sensitivity analyses?
• RQ3 Which parameters most influence scour estimates across the equations?
• RQ4 Do field conditions favor CIRIA C742 and Froehlich equations over others?
• RQ5 How can uncertainty reduction in key parameters improve prediction precision?

Key findings

• Global sensitivity analysis provides more insight than one-at-a-time analysis for scour equations.
• CIRIA and Froehlich equations are most accurate under field conditions.
• Angle of attack, pier shape, and approach flow depth are the most influential parameters across the equations.
• Reducing uncertainty in these three parameters would most increase scour estimate precision.