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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I, Substructure. Item 60, Substructure, is the key item for rating the bridge
foundations for vulnerability to scour damage. When a bridge inspector
finds that a scour problem has already occurred, it should be considered in
the rating of Item 60. Both existing and potential problems with scour
should be reported so that a scour evaluation can be made by others. The
scour evaluation is reported on Item 113 in the revised Recording and
Coding Guide. If the bridge is determined to be scour critical, the rating
of Item 60 should be evaluated to ensure that existing scour problems have
been considered. The following items are recommended for consideration in
inspecting the present condition of bridge foundations:

o evidence of movement of piers and abutment;

- rotational movement (check with plumb line).

- settlement (check lines of substructure and superstructure, bridge
rail, etc. for discontinuities; check for structural cracking or
spall ing).

. check bridge seats for excessive movement.

o damage to scour countermeasures protecting the foundations (riprap,
guidebanks (spur dikes), sheet piling, sills, etc.);

o changes in streambed elevation at foundations (undermining of footings,
exposure of piles; and

o changes in streambed cross.section at bridge including location and
depth of scour holes.

In order to note the conditions of the foundations, the inspector should take
cross sections of the stream, noting location and condition of stream banks.
Careful measurements should be made of scour holes at piers and abutments
probing soft material in scour holes to determine the location of firm bottom.
If equipment or conditions do not permit measurement of the stream bottom, this
condition should be noted for further action.

2. Assessing Scour Potential at 8ridges. The items listed in Table 6.1 are
provided for the bridge inspector's consideration in assessing the adequacy
of the bridge to resist scour. In making this assessment, the inspector
needs to understand and recognize the interrelationships between Item 60
(substructure) Item 61 (channel and channel protection) and Item 71
(Waterway Adequacy). As noted earlier, additional follow-up by others
should be made utilizing Item 113 (Scour Critical 8ridges) when the bridge
inspection reveals a potential problem with scour.

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