fw.1.2 River discharge and hydrographs

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Key terms

• Channel bed roughness
  • The roughness of the channel bed.

• Cross-sectional area
  • The area of the cross-section of water flowing in a channel.

• Discharge
  • The volume of flow of water in a channel, measured in cubic metres per second (cumecs).

• Drainage basin
  • The area of land drained by a river.

• Falling limb
  • The period of time when the river’s discharge is falling after it has reached Peak Discharge.

• Gradient
  • The slope of the river profile (slope angle).

• Hydraulic radius
  • The ratio between the area of the cross-section of a river channel and the wetted perimeter.

• Hydrograph
  • A means of showing the discharge of a river at a given point over a short period of time.

• Impermeable
  • Not permeable.

• Lag time
  • The time between Peak Rainfall and Peak Discharge.

• Laminar flow
  • A horizontal movement of water.

• Load particle size
  • The average size of the sediment particles being transported by a river.

• Load quantity
  • The quantity of sediment that can be transported by a stream/river.

• Meander
  • One of a series of regular sinuous curves in the channel of a river or other watercourse.

• Normal flow
  • Average level of discharge caused by water flowing from tributaries and groundwater.

• Occupied channel width
  • The width of the water within the channel at right angles to the direction of flow.

• Peak discharge
  • The point (time) of maximum river discharge caused by the storm.

• Peak rainfall
  • The hour of greatest rainfall during the storm.

• Permeable
  • A property of soils and rocks indicating their capacity for transmitting water.

• Rising limb
  • The period of rising river discharge following a period of rainfall.

• River mouth
  • The part of a river where it flows into another body of water, such as a sea, ocean or lake.

• Seasonality
  • Refers to the variations in weather, climate, or natural phenomena that occur cyclically and predictably over the course of a year within a specific geographic region. These variations often include changes in temperature, precipitation, and daylight hours, influencing patterns such as the four distinct seasons in temperate regions or the wet and dry seasons in tropical areas.

• Source
  • Where a river starts, usually in the mountains.

• Storm runoff
  • The discharge of the river above Normal Flow, caused by the Storm Event.

• Tributary
  • A smaller river that joins a larger one.