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U.S. Geological Survey
USGS WRIR 00-4151
Online version 1.0

Methodology and Estimates of Scour at Selected Bridge Sites in Alaska

By Thomas A. Heinrichs, Ben W. Kennedy, Dustin E. Langley, and Robert L. Burrows

 

ABSTRACT

The U.S. Geological Survey estimated scour depths at 325 bridges in Alaska as part of a cooperative agreement with the Alaska Department of Transportation and Public Facilities. The department selected these sites from approximately 806 State-owned bridges as potentially susceptible to scour during extreme floods. Pier scour and contraction scour were computed for the selected bridges by using methods recommended by the Federal Highway Administration. The U.S. Geological Survey used a four-step procedure to estimate scour: (1) Compute magnitudes of the 100- and 500-year floods. (2) Determine cross-section geometry and hydraulic properties for each bridge site. (3) Compute the water-surface profile for the 100- and 500-year floods. (4) Compute contraction and pier scour. This procedure is unique because the cross sections were developed from existing data on file to make a quantitative estimate of scour. This screening method has the advantage of providing scour depths and bed elevations for comparison with bridge-foundation elevations without the time and expense of a field survey. Four examples of bridge-scour analyses are summarized in the appendix.

 

CONTENTS

Abstract

Introduction

Background

Purpose and Scope

Methodology

Magnitude of 100- and 500-Year Floods

Cross Sections and Hydraulic Properties

Computation of Water-Surface Profile Using WSPRO Step-Backwater Model

Estimates of Contraction Scour and Pier Scour

Summary and Conclusions

References Cited

Appendix: Summary Examples of Four Phase I Bridge-Scour Analyses

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For questions about the content of this report, contact Robert L. Burrows

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Last update: 15:29:22 Thu 07 Mar 2002
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