Friday, February 8, 2008

SCOUR AT BRIDGES – What's it all about?

What is scour?
Scour is the hole left behind when sediment (sand and rocks) is washed away from the bottom of a river. Although scour may occur at any time, scour action is especially strong during floods.

Swiftly flowing water has more energy than calm water to lift and carry sediment down river

What is involved in a bridge–site examination?

A bridge–site examination for scour begins in the office of the Massachusetts Highway Department, where historical engineering information and bridge plans are reviewed. The examiner then visits the bridge site, walking upstream and downstream from the bridge and taking notes on the condition of the river channel. Other characteristics of the river are noted, such as locations of river bends near the bridge and what possible effects these may have on the bridge. Many things affecting scour are examined, such as the type of rock or sediment carried by the river and the angle at which the river flows toward and away from the bridge. The number of trees growing on the river banks also is noted because tree roots can help keep soil from being washed away. The area under and near a bridge is examined for scour holes and other evidence of scour.

Why be concerned about scour?

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