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

FHWA TECHNICAL ADVISORY T 5140.20
September 16, 1988

b. Paragraph 3 contains the FHW~ recommendations for
developing and implementing a scour evaluation program.
The recommendations have been developed based on the
review and evaluation of the existing policies and
guidance pertaining to bridge scour set forth in
paragraph 4. The interim procedures in the Attachment
provide approaches for implementing these
recommendations.

3. RECOMMENDATIONS FOR DEVELOPING 10ND IMPLEMENTING A SCOUR
EV~LUATION PROGRAM. Every bridge over a scoura.):)le stream,
whether existing or under design, should be evaluated as to
its vulnera.):)ility to floods in order to determdne the prudent
measures to be taken for its protection. Most waterways can
be expected to experience scour over a bridge'S service life
(which is now approaching 100 years). Exceptions might
include waterways in massive, competent rock formations where
scour and erosion occur on a scale that is measured in
centuries. (See Attachment, Chapter 2.) The added cost of
making a bridge less vulnerable to scour is small when
compared to the total cost of a failure which can easily be
two or three times the original cost of the bridge itself.
Moreover, the need to ensure public safety and to minimize
the adverse effects stemming from bridge closures requires
our best effort to improve the state-of-practice of designing
and maintaining bridge foundations to resist t~e effects of
scour. The recommendations listed below serve to summarize
the essential elements which should be addressed in
developing a program for evaluating bridges and providing
countermeasures for scour. Detailed guidance regarding
approaches for implementing the recommendations is included
in the interim procedures in the Attachment.

a. Interdisciplinary Team. Scour evaluations of new and
existing bridges should be conducted by an
interdisciplinary team comprised of structural,
hydraulic, and geotechnical engineers. (See Attachment,
Chapters 3 and 5.)

b. New Bridges. Bridges over tidal and non-tidal waterways
with scoura.):)le beds should withstand the effects of scour
from a superflood (a flood exceeding the 100 year flood)
without failing i.e., experiencing foundation movement of
a magnitude that requires corrective action.

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