Hydrological Characteristics (Cambridge (CIE) IGCSE Geography) : Revision Note

Features of drainage basins

• A drainage basin is the area of land drained by a river and its tributaries

  • This is also known as the catchment area of the river

• Drainage basins are open systems

• This means that as well as stores and transfers, drainage basins have inputs and outputs

  • The input is any water entering the system (precipitation)

  • Outputs are where water is lost from the drainage basin (evaporation, transpiration and into the sea/lake)

• When precipitation falls into the drainage basin, it will take different paths

• The possible paths include:

  • Direct channel precipitation, which occurs when the water falls directly into a river

  • Overland flow (surface runoff) when the water cannot infiltrate the soil due to the ground being impermeable

  • Throughflow when the water flows through the soil

  • Groundwater flow when the water flows through the rocks

• Every drainage basin is unique

• They have different

  • shapes

  • sizes

  • rock types

  • relief

  • land use

Drainage basin features

• All drainage basins have some features in common:

  • The watershed is the boundary between drainage basins

  • A source is the point of the river which is furthest from the mouth; this is the point at which the river begins and is usually an upland lake, spring or glacier

    • Gravity then causes water to flow downhill, taking the fastest and easiest path

  • A confluence is the place where two or more streams/rivers meet

  • Tributaries are streams or rivers flowing into larger streams or rivers

  • The mouth of a river is where it enters the sea/ocean or sometimes a lake

The water cycle & drainage basins

• All drainage basins are part of Earth's hydrological cycle

• The hydrological cycle is a closed system 

• Water is constantly recycled through the system

• The hydrological cycle includes stores and transfers

  • The stores and transfer processes of the hydrological cycle all take place within individual drainage basins

Drainage basin processes

Stores

• Stores are those places where water is held for a period of time

• Stores of the hydrological cycle include:

  • The atmosphere where water is stored in the form of water vapour or as water droplets in clouds

  • Surface stores such as puddles, lakes, rivers and reservoirs

  • Aquifers, which are permeable rocks such as limestone and sandstone which can hold water 

  • Ice and snow

  • Seas and oceans 

• Interception is how precipitation is prevented from reaching the ground, usually by being caught on leaves or branches

  • Some of the water will be stored on the leaves and evaporate into the atmosphere

  • The remaining water will flow down the leaves, branches and trunk until it reaches the ground (stemflow)

Transfers

• Transfers are how water is moved around the hydrological cycle and each drainage basin

• Transfers include:

  • Evaporation is the change of water from a liquid to a gas (water vapour) due to heat from the sun

    • This process transfers water from the surface up into the atmosphere

    • Higher temperatures and strong winds lead to increased evaporation

  • Condensation, which occurs when water cools and changes from water vapour into a liquid (water droplets)

    • Condensation leads to the formation of clouds

  • Transpiration, which occurs when plants release water vapour from their leaves

    • This process transfers water from the plants into the atmosphere

  • Evapotranspiration is the combined transfer of water vapour from the Earth's surface and plants

  • Precipitation is the transfer of water from the atmosphere to the Earth's surface in the form of hail, sleet, rain or snow

  • Overland flow is any water flowing across the Earth's surface

  • When water is transferred from the surface into the soil, this is known as infiltration

  • Percolation is the transfer of water from the soil into the rocks and aquifers

  • Throughflow occurs when water is transferred through the soil between the surface and the water table

  • Groundwater flow is the transfer of water through rocks

  • Channel flow is water flowing in a river or stream