FLOOD04125

• County: Statewide
• Basin: Statewide
• Title: Interim Procedures for Evaluating Scour at Bridges
• Date: 9/1/1988
• Prepared By: Federal Highway Administration
• Floodplain - Doc Type: Educational/Technical/Reference Information

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CHAPTER 5
EVALUATING THE VULNERABILITY OF
EXISTING BRIDGES TO SCOUR

A. INTRODUCTION

Bridges over streams subject to scour should be evaluated to detenaine their
vulnerability to floods and whether they are scour critical. This assesSDent
or evaluation should be conducted by an interdisciplinary team of professional
engineers who can make the necessary engineering judgments to decide:

o priorities for making bridge scour evaluations;

o the scope of the scour evaluations to be performed in the office and in
the field;

o whether or not a bridge is vulnerable to scour damage i.e. whether the
bridge is a scour critical bridge;

o which alternative scour countermeasures may serve to make a bridge less
vulnerable or invulnerable;

o which countermeasure is most suitable and cost-effective for a given
bridge;

o priorities for installing scour countermeasures; and

o monitoring and inspection schedules for scour critical bridges.

The factors to be considered in a scour evaluation require a broader scope of
study and effort than those considered in a bridge inspection. Whereas the
major purpose of the bridge inspection is to identify changed conditions which
may reflect an existing or potential problem, the scour evaluation'is an
engineering assessment of what might possibly happen in the future and what
steps can be taken now to eliminate or minimize future damage.

B. THE EVALUATION PROCESS

The following approach is recommended regarding the development and
implementation of a program to assess the vulnerability of existing bridges to
scour:

STEP 1: Compile a list of those bridges with actual or potential problems with
scour. Structures that are candidates for this category include:

(a) Bridges currently experiencing scour or that have a history of
scour problems during past floods as identified from maintenance
records and experience, bridge inspection records, soundings,
etc.

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