Skip Links

USGS - science for a changing world

Scientific Investigations Report 2008–5161

Prepared in cooperation with the South Dakota Department of Transportation

Estimation of Potential Bridge Scour at Bridges on State Routes in South Dakota, 2003–07

By Ryan F. Thompson and Ryan L. Fosness

Thumbnail of and link to report PDF (9.5 MB)


Flowing water can erode (scour) soils and cause structural failure of a bridge by exposing or undermining bridge foundations (abutments and piers). A rapid scour-estimation technique, known as the level-1.5 method and developed by the U.S. Geological Survey, was used to evaluate potential scour at bridges in South Dakota in a study conducted in cooperation with the South Dakota Department of Transportation. This method was used during 2003–07 to estimate scour for the 100-year and 500-year floods at 734 selected bridges managed by the South Dakota Department of Transportation on State routes in South Dakota.

Scour depths and other parameters estimated from the level-1.5 analyses are presented in tabular form. Estimates of potential contraction scour at the 734 bridges ranged from 0 to 33.9 feet for the 100-year flood and from 0 to 35.8 feet for the 500-year flood. Abutment scour ranged from 0 to 36.9 feet for the 100-year flood and from 0 to 45.9 feet for the 500-year flood. Pier scour ranged from 0 to 30.8 feet for the 100-year flood and from 0 to 30.7 feet for the 500-year flood. The scour depths estimated by using the level-1.5 method can be used by the South Dakota Department of Transportation and others to identify bridges that may be susceptible to scour.

Scour at 19 selected bridges also was estimated by using the level-2 method. Estimates of contraction, abutment, and pier scour calculated by using the level-1.5 and level-2 methods are presented in tabular and graphical formats. Compared to level-2 scour estimates, the level-1.5 method generally overestimated scour as designed, or in a few cases slightly underestimated scour. Results of the level-2 analyses were used to develop regression equations for change in head and average velocity through the bridge opening. These regression equations derived from South Dakota data are compared to similar regression equations derived from Montana and Colorado data. Future level-1.5 scour investigations in South Dakota may benefit from the use of these South Dakota-specific regression equations for estimating change in stream head and average velocity at the bridge.

Version 1.0

Posted September 2008

Downloads Directory

For additional information contact:
Director, USGS South Dakota Water Science Center
1608 Mountain View Road
Rapid City, SD 57702
(605) 394-3220

Part or all of this report is presented in Portable Document Format (PDF); the latest version of Adobe Reader or similar software is required to view it. Download the latest version of Adobe Reader, free of charge.

Suggested citation:

Thompson, R.F., and Fosness, R.L., 2008, Estimation of potential bridge scour at bridges on State routes in South Dakota, 2003–07: U.S. Geological Survey Scientific Investigations Report 2008–5161, 18 p.




Estimated Potential Bridge Scour: Level-1.5 Method

Estimated Potential Bridge Scour: Level-2 Method

Comparison of Scour Estimates Between the Level-1.5 and Level-2 Methods

Assessment of the Suitability of Previously Published Regression Equations to Level-1.5 Scour Analysis in South Dakota

Considerations for Future Estimation of Bridge Scour in South Dakota




Accessibility FOIA Privacy Policies and Notices

Take Pride in America logo logo U.S. Department of the Interior | U.S. Geological Survey
URL: http:// /sir/2008/5161/index.html
Page Contact Information: Contact USGS
Page Last Modified: Thursday, 10-Jan-2013 18:54:31 EST