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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Guide Bank - A dike extending upstream from the approach embankment at
either or both sides of the bridge opening to direct the flow through the opening_
Some guidebanks extend downstream from the bridge.

Hard Point - A streambank protection technique whereby 'soft' or erodible
materials are removed from a bank and replaced by stone or compacted clay. Some
hard points protrude a short distance into the channel to direct erosive currents
away from the bank. Hard points also occur naturally along streambanks as passing
currents remove erodible materials leaving nonerodible materials exposed.

Head-Cuttinq - Channel bottom erosion moving upstream through a basin
indicating that a readjustment uf the basin's slope and its stream discharge and
sediment load characteristics is taking place. Head-cutting is evidenced by the
presence of waterfalls or rapidly moving water through an otherwise placid stream.
Head -cutting often leaves streambanks in an unstable condition as it progresses
through a reach.

Helical Flow - 1 hree-dimensional movement of water particles along a spiral
path in. the general direction of flow. These secondary-type currents are of most
signi ficance as flow paSS'lS throu,]h a bend; their net effect is to remove soil
particles from the cut bank and deposit this material on the point bar.

Historical Flood - The largest known flood event at a given site.

Hydraulics - The applied science concerned with the behavior and flow of
liquids, especially in pipes, channels, structures, and the ground.

Hydraulic Radius - The cross -sectional area of a stream divided by its wetted
perimeter.

Hydraulic Problem - A.n effect of stream flow, tidal flow, or wave action on a
crossing such that traffic is immediately or potentially disrupted, or another
highway detrimental effect is caused.

Hydraulic Model - A small-scale physical representation of a flow situation.

Hydraulic Structures - 1 he facilities used to impound, accomodate, conveyor
control the flow of water, such as dams, weirs, intakes, culverts, channels, and
bridges.

!-iydroqrapt:! - T he graph of stage or discharge against time.

!-iydroloqy - The science concerned with the occurrence, distribution, and
circulation of water on the earth.

Hydrometeoroloqy - 1 he branch of hydrology concerned with the relationship of
precipitation and run -off to climate and weather.

lcinq - Masses or sheets of ice formed on the frozen surface of a ri vcr or
floodplain. When shoals in the river are frozen to the bottom or otherwise dammed,
water under hydrostatic pressure is forced to the surface where it freezes.

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