Discharge (hydrology)

It equals the product of average flow velocity (with dimension of length per time, in m/h or ft/h) and the cross-sectional area (in m2 or ft2).

[1] It includes any suspended solids (e.g. sediment), dissolved chemicals like CaCO3(aq), or biologic material (e.g. diatoms) in addition to the water itself.

Measurement of cross sectional area and average velocity, although simple in concept, are frequently non-trivial to determine.

[2] A commonly applied methodology for measuring, and estimating, the discharge of a river is based on a simplified form of the continuity equation.

The equation implies that for any incompressible fluid, such as liquid water, the discharge (Q) is equal to the product of the stream's cross-sectional area (A) and its mean velocity (

Because the peak flow also corresponds to the maximum water level reached during the event, it is of interest in flood studies.

Analysis of the relationship between precipitation intensity and duration and the response of the stream discharge are aided by the concept of the unit hydrograph, which represents the response of stream discharge over time to the application of a hypothetical "unit" amount and duration of rainfall (e.g., half an inch over one hour).

The amount of precipitation correlates to the volume of water (depending on the area of the catchment) that subsequently flows out of the river.

G. H. Dury and M. J. Bradshaw are two geographers who devised models showing the relationship between discharge and other variables in a river.