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Open-File Report 00-64

Pennsylvania Department of Transportation

Procedures for Scour Assessments at Bridges in Pennsylvania

By Peter J. Cinotto and Kirk E. White

Abstract

Scour is the process and result of flowing water eroding the bed and banks of a stream. Scour at nearly 14,300 bridges1 spanning water, and the stability of river and stream channels in Pennsylvania, are being assessed by the U.S. Geological Survey (USGS) in cooperation with the Pennsylvania Department of Transportation (PennDOT). Procedures for bridge-scour assessments have been established to address the needs of PennDOT in meeting a 1988 Federal Highway Administration mandate requiring states to establish a program to assess all public bridges over water for their vulnerability to scour. The procedures also have been established to help develop an understanding of the local and regional factors that affect scour and channel stability.

This report describes procedures for the assessment of scour at all bridges that are 20 feet or greater in length that span water in Pennsylvania. There are two basic types of assessment: field-viewed bridge site assessments, for which USGS personnel visit the bridge site, and office-reviewed bridge site assessments, for which USGS personnel compile PennDOT data and do not visit the bridge site. Both types of assessments are primarily focused at assisting PennDOT in meeting the requirements of the Federal Highway Administration mandate; however, both assessments include procedures for the collection and processing of ancillary data for subsequent analysis. Date of bridge construction and the accessibility of the bridge substructure units for inspection determine which type of assessment a bridge receives. A Scour-Critical Bridge Indicator Code and a Scour Assessment Rating are computed from selected collected and compiled data. PennDOT personnel assign the final Scour-Critical Bridge Indicator Code and a Scour Assessment Rating on the basis of their review of all data.

1Words presented in bold type are defined in the Glossary section of this report.

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Suggested citation:

Cinotto, P.J., and White, K.E., 2000, Procedures for scour assessments at bridges in Pennsylvania: U.S. Geological Survey Open-File Report 00-64, 210 p.



Contents

Glossary

Abstract

Introduction

Procedures for data collection and processing

Procedure for drainage-basin description and flood-discharge computations by use of a geographic information system

Procedure for computation of Scour-Critical Bridge Indicator Code and Scour Assessment Rating for bridge-scour assessment

Potential applications of data

Summary

References cited

Appendix A - Procedures for completing the “Bridge and Channel Characteristics at Field-Viewed Bridge Sites” form and the “Addendum to Field Form for Non-Accessible Subunits” form

Appendix B - Total-station survey procedures and attributes

Appendix C - Location and identification of global positioning system base stations used in Pennsylvania

Appendix D - Procedure for collection of video-tape data

Appendix E - Form and procedures for completion of the “Bridge and Channel Characteristics at Office-Reviewed Bridge Sites” form

Appendix F - Procedure for determination of the Scour-Critical Bridge Indicator Code for field-viewed bridge sites

Appendix G - Procedure for determination of the Scour-Critical Bridge Indicator Code for office-reviewed bridge sites

Appendix H - Procedure for computation of the Scour Assessment Rating for field-viewed bridge sites

Appendix I - Procedure for computation of the Scour Assessment Rating for office-reviewed bridge sites


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