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 6
INSPECTION OF BRIDGES FOR SCOUR

A. INTRODUCTION

There are two main objectives to be accomplished in inspecting bridges for
scour:

o to accurately record the present condition of the bridge and the stream;
and

o to identify conditions that are indicative of potential problems with
scour and stream stability for further review and evaluation by others.

In order to accomplish these objectives, the inspector needs to recognize and
understand the interrelationship between the bridge, the stream, and the
floodplain. Typically, a bridge spans the main channel of a stream and perhaps
a portion of the floodplain. The road approaches to the bridge lie on
embankments where they obstruct flows on the floodplain. This overbank or
floodplain flow must therefore return to the stream at the bridge and/or
overtop the approach roadways. Where overbank flow is forced to return to the
main channel at the bridge, zones of turbulence are established and scour is
likely to occur at the bridge abutments. Further, piers and, abutments may
present obstacles to flood flows in the main channel, creating conditions for
local scour because of the turbulence around the foundations. After flowing
through the bridge the floodwaters will expand back to the floodplain, creating
additional zones of turbulence and scour.

The following sections in this Chapter present guidance for the bridge
inspector's use in developing a comprehension of the overall flood flow
patterns at each bridge inspected; and to use this information for rating the
present condition of the bridge and the potential for damage from scour. When
an actual or potential scour problem is identified by a bridge inspector, the
bridge should be further evaluated by an interdisciplary team using the
approach discussed in Chapter 5. The results of this evaluation should be
recorded under Item 113 of the 8ridge Recording and Coding Guide (5).

If the bridge is determined to be scour critical, a plan of action (Chapter 7)
should be developed for installing scour countermeasures. In this case, the
rating of the bridge substructure (Item 60) should be revised to reflect the
effect of the scour on the substructure.

8. OFFICE REVIEW

It is desirable to make an office review of bridge plans and previous
inspection reports prior to making the bridge inspection. Information
obtained from the office review provides a better basis for inspecting the
bridge and the stream. Items for consideration in the office review include:

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