FLOOD06421

• County: Statewide
• Basin: Statewide
• Title: Highways in the River Environment
• Date: 2/1/1990
• Prepared By: Federal Highway Administration
• Floodplain - Doc Type: Educational/Technical/Reference Information

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Contraction Scour - Scour of the bed of a channel due to the acceleration of
the flow caused by constr iction.

Countermeasure - A measure, either incorporated into the design of a bridge or
installed separately at or near the bridge, that serves to prevent or control hydraulic
problems.

Crib - A frame structure, filled with earth or stone ballast, designed to absorb
energy and to deflect streamflow away from a bank.

Critical Shear Stress - The minimum amount of shear stress exerted by passing
stream currents that is required to initiate soil particle motion.

Crossinq - The relatively short and shallow reach of a stream between bends;
also called a crossover.

Cross Section - A diagram or draWing cut across a channel that illustrates the
banks, bed, and water surface.

Current - Water flowing through a channel.

Current Meter - An instrument used to measure flow velocity.

!;:ut Bank - The concave wall of a meandering stream.

Cutoff - A natural or artificial channel that shortens the length of a stream;
natural cutoffs may occur either across the neck of a meander loop (neck cutoffs) or
across a point bar (chute cutoffs).

Cutoff Wall - A wall, usually of sheet piling or concrete, that extends from the
flow line down to scour-resistant material or to below a predetermined scour depth.

paily Discharqe - Discharge averaged over one day.

pebris - Material transported by the stream, either floating or submerged, such
as logs or trash that may lodge against the bridge.

Deep Water (for wave~ - Water of such a depth that surface waves are little
affected by bottom conditions; customarily, water deeper than half the wavelength.

Deflector - Alternative term for "spur."

Deqradation (bed) - A progressive lowering of the channel bed due to a change
in the stream's discharge and sediment load characteristics.

Density of Water Sediment Mixture - Bulk density (mass per unit volume)
including both water and sediment.

Desiqn Discharqe - Maximum flow a bridge is expected to accomodate without
contravention of the adopted design constraints.

Desiqn Hiqh-Water Level - The maximum water level that a bridlJe opening is
designed to accommodate without contravention of the adopted design constraints.

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