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GCSE Geography > Drainage Basins

Some definitions:
  • Watershed - the boundary of the drainage basin formed by the highest points of mountains / hills forming a ring around the drainage basin
  • Tributary - a smaller offshoot of a main river
  • Confluence - the point at which two rivers meet
  • Source - where the river starts (usually high up in the mountains or hills)
  • Lag time - the time between the peak rainfall and the peak water discharge from the river
There are different types of drainage basins which behave in various ways due to some factors which are listed below:
  • Relief of the land
  • Rock type
  • Soil
  • Vegetation
  • Land use
  • Use of rivers by man
  • Drainage density

If the relief is made up of steep slopes this will lead to faster surface run-off of the rain therefore a lot of it will go straight into the river.

Impermeable rock will cause more surface run-off whereas permeable (porous) rock will allow through flow and ground water flow. This slows the water down, increasing the lag time and reducing the peak discharge of the river.

If the soil is very thin there will be less infiltration but if it is deeper, more infiltration will occur.

Where there is little vegetation and just thin grass and moor land etc... there will be less interception compared to forest areas for example. Roots delay through flow and absorb moisture and evapo-transpiration also reduces the chances of the water reaching the river so quickly.

Urbanisation of an area means an increased amount of tarmac and drains therefore surface run-off will be increased.

If water is extracted for industry, domestic use, or irrigation, this will reduce the amount of water flowing down the river all at once. Building a dam means that water can be stored and the river's water level can be regulated.

A large network of smaller streams to collect water more quickly will mean that the water will flow very quickly to the bottom of the river which could cause a dramatic increase in the water level over a short period of time. Fewer streams allows more time for infiltration etc...

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