Glossary Related to Sediment Transport - Sediment Transport in Irrigation Canals: A New Approach - page 277

Flow control method In general, a regulation method for irrigation structures to maintain a

specific flow condition in the irrigation system.

Flow, steady- Flow in which the depth and velocity remain constant with respect to time.

Flow, uniform- Flow in which the depth and velocity remain constant with respect to

space.

Free flow Flow through a canal, which is not affected by the level of the downstream

water.

Free water level Level or surface of a body of water in free contact with the atmosphere,

meaning at atmospheric pressure.

Freeboard The difference in elevation of the maximum (normal) flow line and the

ground surface or bank at a canal or drain section. Also the vertical distance
between the maximum water surface elevation in design and the top of
retaining banks or structures, provided to prevent overtopping because
of unforeseen conditions.

Free-surface Interface between a liquid and a gas. More generally a free surface is the

interface between the fluid (at rest or in motion) and the atmosphere.

Friction Boundary shear resistance of the wetted surface of a channel, which

opposes the flow of water; process by which energy is lost through shear
stress.

Friction coefficient Coefficient used to calculate the energy gradient by friction.

Froude William Froude (1810-1879) - English naval architect and hydro-

dynamicist who used the law of similarity to study the resistance of model
ships.

Froude number A dimensionless number represe n ting the ratio of inertia forces and gravity

forces acting upon water. Fr 2 v 2 /gy .

It is used to differentiate open channel flow regimes and to distinguish
between sub-critical and super-critical flow.

=

Gauge Device for measuring water level, discharge, velocity, pressure, etc.,

relative to a datum.

Gauge datum Fixed plane to which the water level is related; the elevation of the zero of

the gauge is related to this plane.

Gauge height Elevation of water surface measured by a gauge.

Gradient Measure of slope in metre of rise or fall per metre of horizontal distance;

dimensionless.

Gradually varied flow Flow characterized by relatively small changes in velocity and pressure

distributions over a short distance.

Head Potential energy of water due to its height above a datum or reference level,

usually expressed in m.

Head works The main intake structure of an irrigation system, often equipped with a

weir or barrage, an intake sluice, sediment excluder or sand trap.

Head-discharge
relationship

Curve or table which gives the relation between the head and the discharge
in an open channel at a given cross-section for a given flow condition,
e.g. steady, rising or falling.