turbulence:
Motion of fluids in which local velocities and pressures fluctuate
irregularly in a random manner as opposed to laminar flow
where all particles of the fluid move in distinct and separate
lines.
ultimate scour:
The maximum depth of scour attained for a given flow
condition. May require multiple flow events and in cemented or
cohesive soils may be achieved over a long time period.
uniform flow:
Flow of constant cross section and velocity through a reach of
channel at a given time. Both the energy slope and the water
slope are equal to the bed slope under conditions of uniform
flow.
unit discharge:
Discharge per unit width (may be average over a cross section,
or local at a point).
unit shear force
The force or drag developed at the channel bed by flowing
(shear stress):
water. For uniform flow, this force is equal to a component of
the gravity force acting in a direction parallel to the channel bed
2
on a unit wetted area. Usually in units of stress, Pa (N/m ) or
2
(lb/ft ).
unsteady flow:
Flow of variable discharge and velocity through a cross section
with respect to time.
upper bank:
The portion of a streambank having an elevation greater than
the average water level of the stream.
velocity:
The time rate of flow usually expressed in m/s (ft/sec). The
average velocity is the velocity at a given cross section
determined by dividing discharge by cross-sectional area.
vertical abutment:
An abutment, usually with wingwalls, that has no fill slope on its
streamward side.
vortex:
Turbulent eddy in the flow generally caused by an obstruction
such as a bridge pier or abutment (e.g., horseshoe vortex).
wandering channel:
A channel exhibiting a more or less non-systematic process of
channel shifting, erosion and deposition, with no definite
meanders or braided pattern.
wandering thalweg:
A thalweg whose position in the channel shifts during floods
and typically serves as an inset channel that conveys all or
most of the stream flow at normal or lower stages.
lvi
Previous Page
