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

FIGURE 4.7 Bridge Abutment in Main Channel and Overbank Flow

Equation 6 or 8 should be used to calculate the scour depth .ith abutment
length a determined by equation 9. Engineering judgment must be used in
selecting the scour depth for design purposes. Equation 10 can also be used
for this case with the appropriate selection of variables.

Live bed scour (t, > te) use equations 6 and 10.
Clear water scour (t, < te) use equations 8 and 10.

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CASE 2 AButMENT PROJECTS INTO THE CMANNEL. OVERBANK FLOW

No bed material is transported and a/y, < 25.
Figure 4.7.

This case is illustrated in

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~

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y

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~

,----------------
~

a =

Qo
V,y,

(9)

t, = The shear stress in the main channel.
te = The critical shear stress for the bed material in the
main channel. The value can be determined from Figure 4.5.
Qo = Flow obstructed by abutment and bridge approach.
y, = Average upstream flow depth in the main channel.
V, = Average velocity in the main channel.

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