Summary

Drainage basins are open systems, with inputs, stores and outputs. The main input is precipitation which is regulated by various means of storage. Outputs include channel runoff, evapotranspiration and groundwater flow.

 

The Drainage basin system

Drainage basin flow chart

Drainage basin flow chart

 
 
Drainage basin system diagram. (Click on the image above to obtain a downloadable PDF)

Drainage basin system diagram. (Click on the image above to obtain a downloadable PDF)

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TASK

  1. Complete the system diagram using information from the flow chart
  2. Identify and annotate a feedback loop on your system diagram
  3. Make notes on pp 104-106 Core Book
 

water balance in a drainage basin

Water balance in a drainage basin (Source)

Water balance in a drainage basin (Source)

The water balance is the relationship between inputs (precipitation) and outputs (evapotranspiration). It is influenced by a number of factors:

  • Soil moisture deficit - the degree to which soil moisture falls below its capacity
  • Soil moisture recharge - precipitation > potential EVT
  • Soil moisture surplus - soil is saturated leading to overland flow
  • Soil moisture utilisation - water is drawn to the surface by the capillary action of plants, which is then used or evaporated

These factors may change over time (seasons, long term changes in ice/water balance) or space (precipitation, EVT and runoff vary between countries).

 

PLENARY

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