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The Water Balance
Water balance is worked out from inputs and outputs.
The water balance affects how much water is stored in the basin.
The balance between water inputs and outputs of a drainage basin may be shown as a
water budget graph.
It is expressed as follows:
P = Q + E (+/- change in storage)
P = precipitation
Q = run-off
E = evapotranspiration
The diagram below illustrates the main features of the water balance:
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Surplus: If precipitation exceeds evapotranspiration and the excess is not been used by
Deficiency: Evapotranspiration exceeds precipitation
Recharge: Replacement of water lost during drier periods
The maximum amount of water soil can hold.
A water surplus can result in wet soils, high river levels and run-off whereas a deficit leads to
dry soil, falling river levels and possibly drought. Management is shown in the example at
the end of this topic.…read more