FLOOD05322

• County: Statewide
• Basin: Statewide
• Title: Evaluating Scour at Bridges
• Date: 1/1/1993
• Prepared By: Federal Highway Administration
• Floodplain - Doc Type: Educational/Technical/Reference Information

GLOSSARY

abrasion:

Decrease in particle size or riprap size resulting from contact with other
particles. Removal of streambank or bridge foundation material due to
entrained sediment, ice, or debris rubbing against the bank or foundation.

aggradation:

General and progressive buildup of the longitudinal profile of a channel
bed due to sediment deposition,

alluvium:

Unconsolidated material deposited in water by a stream,

alluvial channel:

Channel wholly in alluvium; no bedrock is exposed in channel at low
flow or likely to be exposed by erosion,

alluvial fan:

A fan-shaped deposit of material at the place where a stream issues from
a narrow valley of high slope onto a plain or broad valley of low slope,
An alluvial cone is made up of the finer materials suspended in flow
while a debris cone is a mixture of all sizes and kinds of materials,

alluvial stream:

A stream wbich has fonned its channel in cohesive or non-cohesive
materials that have been and can be transported by the stream,

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alternating bars:

Elongated deposits found alternately near the right and left banks of a
channel.

anabranch:

Individual channel of an anabranched stream.

anabranched stream:

A stream whose flow is divided at nonnal and lower stages by large
islands or, more rarely, by large bars; individual islands or bars are
wider than about three times water width; channels are more widely and
distinctly separated than in a braided stream,

apron:

Protective material laid on a streambed to resist scour,

apron, launching:

An apron designed to settle and protect the sideslopes of a scour hole
after settlement.

armor:

Surfacing of channel bed, banks, or embankment slope to resist erosion
and scour,

armoring:

(a) Natural process whereby an erosion-resistant layer of relatively large
particles is fonned on a streambed due to the removal of finer particles
by streamflow; (b) placement of a covering to resist erosion,

articulated concrete mass:

Rigid concrete slabs which can move without separating as scour occurs;
usually hinged together with corrosion-resistant wire fasteners; primarily
placed for lower bank protection.

average velocity:

Velocity at a given cross section detennined by dividing discharge by
cross sectional area.

avulsion:

A sudden change in the channel course that usually occurs when a
stream breaks through its banks; usually associated with a flood or a
catastrophic event.

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