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

3. DOWNSTREAM CONDITIONS

a. Banks

Stable Natural vegetation, trees, bank stabilization measures
such as riprap, paving, gabions, channel stabilization
measures such as dikes and grains.

Unstable Bank scuffing, undermining, evidence of lateral
movement, damage to stream stabilization installation's,
etc.

b. Main Channel

clear and open with good "getaway. conditions, or meandering or
braided with bends, islands, bars, cattle guards, and fences that
retard and obstruct flow.

Aggrading or degrading stream bed.

Evidence of downstream movement of channel with respect to the
bridge (..ke sketches and take pictures.)

c. Floodplain

Clear and open so that contracted flow at bridge will return
smoothly to floodplain, or restricted and blocked by dikes,
developments, trees, debris, or other obstructions.

Evidence of scour and erosion due to downstream turbulence.

d. Other Features

Downstreaa dams or confluences with larger stream which may cause
variable tailwater depths. (This may create conditions for high
velocity flow through bridge.)

D. UNDERWATER IISPECTIONS

Perhaps the single most important aspect of inspecting the bridge for actual or
potential damage fro. scour is the taking and plotting of measurements of
stream bottom elevations in relation to the bridge foundations. Where
conditions are such that the stream bottom cannot be accurately measured by
rods, poles, sounding lines or other means and the condition of the foundations
determined, then other arrangements need to be made. Other approaches to
determining the cross-section of the streambed at the bridge include:

o use of divers; and

o use of electronic scour and radar equipment (See Appendix E).

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