armor (armoring):
Surfacing of channel bed, banks, or embankment slope to
resist erosion and scour. (a) Natural process whereby an
erosion- resistant layer of relatively large particles is formed on
a streambed due to the removal of finer particles by
streamflow; (b) placement of a covering to resist erosion.
articulated concrete
Rigid concrete slabs which can move without separating
mattress:
as scour occurs; usually hinged together with corrosion-
resistant cable fasteners; primarily placed for lower bank
protection.
average velocity:
Velocity at a given cross section determined by dividing
discharge by cross sectional area.
avulsion:
A sudden change in the channel course that usually occurs
when a stream breaks through its banks; usually associated
with a flood or a catastrophic event.
The material used to refill a ditch or other excavation, or the
process of doing so.
backwater:
The increase in water surface elevation relative to the elevation
occurring under natural channel and floodplain conditions. It is
induced by a bridge or other structure that obstructs or
constricts the free flow of water in a channel.
backwater area:
The low-lying lands adjacent to a stream that may become
flooded due to backwater.
bank:
The sides of a channel between which the flow is normally
confined.
bank, left (right):
The side of a channel as viewed in a downstream direction.
bankfull discharge:
Discharge that, on the average, fills a channel to the point of
overflowing.
bank protection:
Engineering works for the purpose of protecting streambanks
from erosion.
bank revetment:
Erosion-resistant materials placed directly on a streambank to
protect the bank from erosion.
bar:
An elongated deposit of alluvium within a channel, not
permanently vegetated.
base floodplain:
The floodplain associated with the flood with a 100-year
recurrence interval.
bed:
The bottom of a channel bounded by banks.
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