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Potential Drift Accumulation at Bridges

GLOSSARY

Accretion: growth by gradual external addition of elements
Boom: a series of connected floating units designed to deflect or contain floating material
Cofferdam: a watertight enclosure pumped dry to allow construction below water level
Debris flow: non-Newtonian flow of a dense, plastic mixture of soil, rock, water, and trees
Debris torrent: debris flow occurring in a steep stream channel
FHWA: Federal Highway Administration
Flood plain: the area of a valley bottom outside the stream channel and covered by water during floods
Freeboard: the distance between the water level and the lowest part of a bridge superstructure
Hydrostatic forces: forces generated by the weight of standing water
Landslide: gravity-driven movement of a mass of soil or rock
Lingulate bar: mid-channel sediment bar with a gently rising upstream face and a steep downstream face
Low steel: the lowest horizontal part of the bridge superstructure. When the water level is at or above low steel, the superstructure is partly immersed.
Point bar: a sediment bar that forms along the base of the convex bank of a channel bend
Scroll bar: a longitudinal sediment bar in the channel parallel to the convex bank of a channel bend
Thalweg: the line of greatest depth along a stream channel
Thread: the line of fastest flow at the water surface. The thread often, but not always, lies over the thalweg.
Trash rack: a grating or series of pilings for retaining floating objects
USGS: United States Geological Survey
Wind throw: the uprooting of a tree by wind
WSPRO: a one-dimensional, steady-flow step-backwater model containing specialized routines for bridge contractions, multiple openings, and supercritical-flow reaches.

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