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Scientific Investigations Report 2009–5099

Prepared in cooperation with the South Carolina Department of Transportation

Development and Evaluation of Live-Bed Pier- and Contraction-Scour Envelope Curves in the Coastal Plain and Piedmont Provinces of South Carolina

By Stephen T. Benedict and Andral W. Caldwell

ABSTRACT

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The U.S. Geological Survey, in cooperation with the South Carolina Department of Transportation, used ground-penetrating radar to collect measurements of live-bed pier scour and contraction scour at 78 bridges in the Piedmont and Coastal Plain Physiographic Provinces of South Carolina. The 151 measurements of live-bed pier-scour depth ranged from 1.7 to 16.9 feet, and the 89 measurements of live-bed contraction-scour depth ranged from 0 to 17.1 feet. Using hydraulic data estimated with a one-dimensional flow model, predicted live-bed scour depths were computed with scour equations from the Hydraulic Engineering Circular 18 and compared with measured scour. This comparison indicated that predicted pier-scour depths generally exceeded the measured pier-scour depths, and at times predicted pier-scour depths were excessive (overpredictions were as large as 23.1 feet). For live-bed contraction-scour depths, predicted scour was sometimes excessive (overpredictions were as large as 14.3 feet), but often observed contraction scour was underpredicted.

For live-bed pier scour, trends in laboratory and field data were compared and found to be similar. The strongest explanatory variable was pier width, and an envelope curve for assessing the upper bound of live-bed pier scour was developed using pier width as the primary explanatory variable. Relations in the live-bed contraction-scour data also were investigated, and several envelope curves were developed using the geometric-contraction ratio as the primary explanatory variable. The envelope curves developed with the field data have limitations, but the envelope curves can be used as supplementary tools for assessing the potential for live-bed pier and contraction scour in South Carolina.

Data from this study were compiled into a database that includes photographs, measured scour depths, predicted scour depths, limited basin characteristics, limited soil data, and modeled hydraulic data. The South Carolina database can be used in the comparison of sites with similar characteristics to evaluate the potential for scour. In addition, the database can be used to evaluate the performance of various analytical methods for predicting live-bed pier and contraction scour.

First posted May 20, 2009

  • Report PDF (10.3 MB)
  • Database directory (Note: Two versions of the Access database exist. The version without photographs is only a megabyte, while the version with photographs is 836 megabytes.)

For additional information contact:
Stephen T. Benedict, Hydrologist
USGS South Carolina Water Science Center
Field Headquarters
405 College Avenue, Suite 200
Clemson, SC 29631
http://sc.water.usgs.gov

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:

Benedict, S.T., and Caldwell, A.W., 2009, Development and evaluation of live-bed pier- and contraction-scour envelope curves in the Coastal Plain and Piedmont Provinces of South Carolina: U.S. Geological Survey Scientific Investigations Report 2009–5099, 108 p.



Contents

Abstract

Introduction

Approach

Data Collection

Development of the Predicted Bridge-Scour Database

Development of the South Carolina Live-Bed Pier-Scour Envelope Curve

Evaluation of Selected Methods for Predicting Live-Bed Pier Scour in South Carolina

Guidance for Evaluating Live-Bed Pier-Scour Depth in South Carolina

Development of the South Carolina Live-Bed Contraction-Scour Envelope Curves

The South Carolina Live-Bed Pier- and Contraction-Scour Database

Summary

Selected References

Appendix 1. Explanation of Variables in the South Carolina Live-Bed Pier- and Contraction-Scour Database

Appendix 2. South Carolina bridge-scour study sites and reference numbers for figure 2


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