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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!3edrock - The solid rock underlying soils and overlying the mantle rock, ranging
from surface exposure to depths of several hundred feet.

!'led Shear (tractive force) - T he force per unit area exerted by a fluid flowing
past a stationary boundary.

Bed Slope - The inclination of the channel bottom.

Bituminous Mattress - An impermeable rock-, mesh-, or metal-reinforced layer
of asphalt or other bituminous material placed on a streambank to prevent erosion.

Blanket - Material covering all or a portion of a streambank to prevent erosion.

!3oulder - A rounded or angular fragment of rock the diameter of which is the
size range of 250 to 4,000 mm.

j=3raig - A subordinate channel of a braided stream.

Braided Stream - A stream whose flow is divided at normal stage by small
mid-channel bars or small islands; the individual width of bars and islands is less
than about three times the water width; a braided stream has the aspect of a single
large channel within which subordinate are channels located.

!3ridqe - A structure, including supports, erected over a depression or an
obstruction such as a body of water, a road, or a railway having a track or
passageway for carrying traffic and a length of opening greater than 20 ft.

Bridqe Openinq - The cross-sectional area beneath a bridge structure that is
available for conveyance of water.

Bridqe Waterway - The area of a bridge opening available for flow, as measured
below a specified stage and normal to the principal direction of flow.

Buffer Zone - Areas of trees, grass or other vegetation located between top
bank and the adjacent highway (also called greenbelts).

Bulkhead - A steep or vertical wall that supports a natural or artificial
embankment and may also serve as a protective measure against erosion.

Cation-Exchanqe Capacity (CEC) - The sum total of exchangeable cations that
a soil can absorb; expressed in milliequivalents per gram or 100 grams of soil.

Causeway - Rock or earth embankment carrying a roadway across water.

Cavinq - The collapse of a bank by undercutting due to wearing away of the toe
or an erodible soil layer above the toe.

Channel - The bed and banks that confine the surface flow of a natural or
man-made stream; braided streams have multiple subordinate channels that are
within the main stream channel; anabranched streams have more than one channel.

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