Bridge Scour - Angle of Attack 1

[froude]

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.

 

[SMIAH]

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).

 

[francesca]

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.

 

[froude]

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.

 

[SMIAH]

Checked for online publications.

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