Glossary Related to Sediment Transport - Sediment Transport in Irrigation Canals: A New Approach - page 275

Cross-section Section of a stream normal to the flow direction bounded by the wetted

perimeter and the free surface.

Darcy-Weisbach friction
factor

Dimensionless parameter characterizing the friction loss in a flow.

Datum Any permanent line, plane or surface used as a reference datum to which

elevations are referred.

Degradation Lowering of channel bed elevation resulting from the erosion of sediments;

downward and lateral erosion.

Density Mass (in kg) per unit of volume of a substance.

Depth, hydraulic or
mean-

Depth obtained by dividing the cross-sectional area by the free surface or
top width.

Design discharge A specific value of the flow rate, which after the frequency and the

duration of exceedance have been considered, is selected for designing
the dimensions of a structure or a system or a part thereof.

Design flow Flow on which the cross sectional area of a canal or drain is determined.

Design flow depth Depth of water in a channel when design flow moves through the cross-

sectional area.

Desilting basin Canal section with very low velocity, forming deposition of the sediment

carried by the water.

Diffusion The process whereby particles intermingle as the result of spontaneous

movement and move from a region of higher concentration to one of lower
concentration. Turbulent diffusion describes the spreading of particles
caused by turbulent agitation.

Diffusion coefficient Quantity of a substance that passes through each unit of cross-section per

unit of time.

Dimensional analysis Technique to reduce the complexity of a problem, by expressing the relevant

parameters in terms of numerical magnitude and associated units, and
grouping them into dimensionless numbers.

Discharge Volume of water per unit time flowing along a pipe or channel, or the

output rate of plant such as a pump.

Discharge regulator Structure regulating the flow from one canal to another.

Diversion structure Structure in a river or canal to divert all or some of the water into a

(diversion) canal.

Drawdown curve Water surface profile, when water surface slope is larger than bottom slope.

Drop A rapid change of bed elevation, also called a step.

Dry density Mass of soil per unit of volume on dry weight basis.

Dunes Types of bed form indicating significant sediment transport over a sandy

bed.

Dynamic equilibrium Short-term morphological changes that do not affect the morphology over

a long period.

Dynamic viscosity The ratio between the shear stress acting along any plane between neigh-

bouring fluid elements and the rate of deformation of the velocity gradient
perpendicular to this plane.