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

(b) Bridges over streams with erodible beds with design features that
make them vulnerable to scour including:

(1) piers and abutments designed with spread footings or short
pile foundations;

(2) superstructures with simple spans or non-redundant support
systems that render them vulnerable to collapse in the event
of foundation movement; and

(3) bridges with inadequate waterway openings or with designs
that collect ice and debris. Particular attention should be
given to structures where there are no relief bridges or
embankments for overtopping, and where all water must pass
through or over the structure.

(c) Bridges on aggressive streams and waterways including those with:
(1) active degradation or aggredation of the stream bed;
(2) significant lateral movement or erosion of stream banks;
(3) steep slopes or high velocities;
(4) gravel or mining operations in the vicinity of the bridge;
and

(5) histories of having damaged highways and bridges during past
floods.

(d) Bridges located on stream reaches with adverse flow
characteristics including:

(1) crossings near stream confluences, especially bridge
crossings of tributary streams near their confluence with
1 arger streams;

(2) crossings on sharp bends in a stream; and

(3) locations on alluvial fans.

STEP 2 Prioritize the list compiled in step 1, using the following factors as
a guide:

(a) The potential for bridge collapse or for damage to the bridge in
the event of a major flood.

(b) The functional classification of the highway on which the bridge
is located, and the effect of a bridge collapse on the safety of
the travelling public and on the operation of the overall
transportation system for the area or region.

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