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

Note 4. Liu, et al's equations are for a dune bed configuration. Therefore,
for a dune bed configuration in the natural stream the scour given by
their equations are for equilibrium scour and for maximum scour the
values must be increased by 30 percent. For plane bed and antidune
flow there are no equations given but it is suggested that Liu, et
al's equations could be used as given unless the anti dunes would be
occurring at the abutment. If anti dunes are or there is the
possibility that they might break at the abutment then the scour depth
given by their equation be increased by 20 percent.

Note 5. Laursen's equations require trial and error solution. Curves
developed by Chang (1987) are given in Figure 4.6. Note that the
equations have been truncated at a value of y./y equal to 4.

Note 6. These equations were developed froa laboratory and theoretical studies
with very little field data. The values obtained should be evaluated
very carefully.

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40 &0 10 100

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Figure 4.5 Critical shear stress as a function of bed material size
and suspended fine sediment.

32

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