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Bridge Scour - Angle of Attack

Bridge Scour - Angle of Attack

Bridge Scour - Angle of Attack

(OP)
What is the best way to define and evaluate the angle of attack as it pertains to Bridge Scour?  I have searched online, but I'm hoping somebody here can clarify it for me a little more.

Thanks in advance.

RE: Bridge Scour - Angle of Attack

I define the angle of attack of approach flow with aerial photography and with topographic map survey. Or, i'm not sure whether this is the appropriate method.

FHWA HEC-18 doesn't provide alot of information on it. From what I know, the angle of attack can make a significant difference in the calculated pier scour.

I guess that this has to be estimated during a representative event of what you want to model on the site (e.g. a flood).  

RE: Bridge Scour - Angle of Attack

Angle of attack for piers is the approach angle of the water in a flood. Look at the entire floodplain rather than the channel immediately upstream of the crossing. If you have in-line piers they need to be at the angle of flow over the overbanks rather than in the channel.

RE: Bridge Scour - Angle of Attack

(OP)
SMIAH, you verbalized my problem better than I could.  In my limited work with bridge scour, I also noticed that the attack angle can make a huge difference in the resulting scour envelope, but HEC-18 doesn't do much to clarify how the angle should be calculated.

I appreciate yours and francesca's input.  Any further input from anybody would be appreciated also.

RE: Bridge Scour - Angle of Attack

Checked for online publications.

Found nothing else than : "Greater skew = greater scour"!

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