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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Proiect Flood - A flood discharge value adopted for the design of projects such
as dams and flood control works.

Quarry-Run Stone - Natural material used for streambank protection as
received from a quarry without regard to gradation requirements.

Railbank Protection -- A type of countermeasure composed of rock-filled wire
fabric and supported by steel rails or posts driven into the streambed.

Rapid Orawdown - Lowering the water against a bank more quickly than the
bank can drain which can leave the bank in an unstable condition.

Reach - A segment of stream length that is arbitrarily bounded for purposes of
study.

Recurrence Interval (R.I.); Return Period; Exceedance Interval - 1 he reciprocal
of the annual probability of exceedance of a hydrologic event.

RefLlsal - Erosion-resistant material placed in a trench (excavated landward) at
the upstream end of a revetment to prevent flanking.

)3einforced-Earth Bul.khead - A retaining structure consisting of vertical panels
and attached to reinforcing elements embedded in compacted backfill for supporting
a natural or artificial streambank (a specific type of retaining wall).

Reinforced Revetment - A streambank protection method consisting of a
continuous stone toe-fill along the base of a bank slope with intermittent fillets of
stone placed perpendicular to the toe and extending back into the natural bank.

Reqime - General pattern of variation around a mean condition, as in flow
regime, tidal regime, channel regime, sediment regime, etc.; used also to mean a set
of physical characteristic,; of a river.

)3~jme Channel - Alluvial channel that has attained more or less a staLe of
equilihrium with respect to erosion and deposition.

Reqime Chanqe - 1\ change in channel characteristics resulting from such
things as changes in imposed flows, sediment loads or slope.

)3eqime Formula - A formula relating stable alluvial channel dimensions or
slope to discharge and sediment characteristics.

Relief Bridqe - An opening in an embankment on a floodplain to permit passage
of overbank flow.

Retaininq Wall - A structure used to maintain an elevation differential between
the water surface and top bank while at the same time preventing bank erosion and
instability.

Retard - A permeable or impermeable linear structure in a channel, parallel
with --the bank and usually at the toe of the bank, intended to reduce flow velocity,
induce deposition, or deflect flow from the bank_

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