FLOOD05322

• County: Statewide
• Basin: Statewide
• Title: Evaluating Scour at Bridges
• Date: 1/1/1993
• Prepared By: Federal Highway Administration
• Floodplain - Doc Type: Educational/Technical/Reference Information

dike:

An impermeable linear structure for the control or containment of
overbank flow, A dike trending parallel with a streambank differs from
a levee in that it extends for a much sborter distance along the bank, and
it may be surrounded by water during floods.

dike (groin, spur, jetty):

A structure extending from a bank into a channel that is designed to: (a)
reduce the stream velocity as the current passes through the dike, thus
encouraging sediment along the bank (permeable dike); or (b) deflect
erosive current away from the stream bank (impermeable dike),

dominant discharge:

(a) The discharge which is of sufficient magnitude and frequency to have
a dominating effect in determining the characteristics and size of the
stream course, channel and bed, (b) That discharge which determines
the principal dimensions and characteristics of a natural channel. The
dominant formative discharge depends on the maximum and mean
discharge, duration of flow, and flood frequency, For hydraulic
geometry relationships, it is taken to be the bank full discharge which
has a return period of approximately 1.5 years in many natural channels,

drift:

Alternative term for "debris,"

ebb or ebb tide:

Flow of water from the bay or estuary to the ocean,

eddy current:

A vortex-type motion of a fluid flowing contrary to the main current,
such as the circular water movement that occurs when the main flow
becomes separated from the bank,

emphemeral stream:

A stream or reach of stream that does not flow for parts of the year. As
used here, the term includes intermittent streams with flow less than
perennial,

entrenched stream:

Stream cut into bedrock or consolidated deposits.

erosion:

Displacement of soil particles on the land surface or in a stream due to
water or wind action,

erosion control matting:

Fibrous matting (e,g" jute, paper, etc,) placed or sprayed on a
streambank for the purpose of resisting erosion or providing temporary
stabilization until vegetation is established,

equilibrium scour:

Scour depth in sand-bed stream with dune bed about which live bed pier
scour level fluctuates due to variability in bed material transport in the
approach flow,

estuary:

Tidal reach at the mouth of a river.

fabriform:

Grout-filled fabric mattress used for stream bank protection,

fetch:

The area in which waves are generated by wind having a rather constant
direction and speed; sometimes used synonymously with fetch length,

fetch length:

The horizontal distance (in the direction of the wind) over which wind
generates waves and wind setup,

fill slope:

Side or end slope of an earth fill embankment.

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