3. Discharge of a River

Discharge

The amount of water across the full width of a river flowing past a point in a given time. Measured in cubic metres per second (cumecs / m³/s).

Storm Hydrograph

A graph showing the rise and fall of a river's water level (discharge) during and after a rainstorm. Records the discharge figures over time.

Annual Hydrograph

A graph showing the discharge of a river over an entire year.

Cumec

The unit used to measure river discharge = cubic metres per second (m³/s).

Laminar Flow

Water flows smoothly over a smooth surface in thin layers/sheets. Little friction, can achieve high speed. Water does NOT change levels. Associated with a flat, even riverbed.

Turbulent Flow

Water flows in a bubbling, chaotic motion. The riverbed is UNEVEN so water continuously changes levels, creating much internal friction. This reduces the speed of flow.

Where is flow speed highest in a straight river?

In the MIDDLE of the water, just below the surface — least frictional drag from the bed, banks and surface.

Where is flow speed highest in a meandering river?

Toward the OUTER bank of the meander — where erosion occurs.

Factor: Amount of rainfall and discharge

More rain → more surface runoff → higher discharge.

Factor: Gradient and discharge

Steeper gradient → water flows faster → higher discharge.

Factor: Soil type and discharge

Impermeable soil → less infiltration → more runoff → higher discharge. Permeable soil → more infiltration → lower discharge.

Factor: Rock type and discharge

Impermeable rock → no infiltration → more runoff → higher discharge.

Factor: Vegetation and discharge

Dense vegetation → more interception and transpiration → less runoff → lower discharge.

Factor: Human activities and discharge

Urbanisation (tar, concrete) → less infiltration → more runoff → higher discharge. Dams reduce discharge downstream.

Factors That Influence Discharge?

• Amount of rai

• Gradient of the land

• Soil type

• Rock type

• Vegetation

• Human activities