River discharge

River discharge is the volume of water passing through a river channel per unit time, commonly expressed in cubic metres per second.

Continuity equation: A conservation equation stating that fluid flow rate equals cross-sectional area multiplied by average velocity. It gives the basic relation used to estimate discharge from channel area and water speed.
Cross-sectional area: The area of a two-dimensional section formed by cutting across an object or flow. River discharge depends on the area of the channel section carrying water.
Flood forecasting: The prediction of future flood conditions using observations, models, and forecasts of precipitation or other inputs. Rising discharge signals flood development and helps estimate downstream risk.
Runoff: Water that flows over land or through shallow subsurface pathways toward streams and other water bodies. Runoff entering a channel changes its discharge.
River stage: The height of a river’s water surface above a specified datum. Stage is a water-level observation, not a volume-per-time flow rate.
Current meter: An instrument that measures water velocity at a point, often using a rotating rotor or acoustic signals. Velocity measurements across a river section support discharge calculations.
Flow velocity: The distance a fluid travels per unit time in a specified direction. Average velocity combines with channel area to determine discharge.
Water resources management: The planning and control of water allocation, storage, use, and protection. Discharge records quantify available river water for competing uses.
Hydrograph: A graph showing how a river’s stage or discharge changes over time. A hydrograph displays the timing and magnitude of discharge variation.
Specific discharge: Discharge divided by the area of the drainage basin, expressing flow per unit catchment area. It normalizes discharge by basin size, enabling comparisons between catchments.

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