Water Balance

1. Water Balance
Year 12 geography GCE

2. What is the water balance / budget?
In order to gain a better understanding of water resources in a drainage basin,
we use a simple equation called the water balance. This is expressed as follows:
Rivers are present on the surface only if the stores are capable of releasing
water and if there is direct surface runoff.

3. What is the water balance / budget?
When precipitation is greater than evapotranspiration the pores of the soil are
refilled with water – soil moisture recharge.
When the soil becomes saturated, excess water will have difficulty infiltrating
into the ground – soil moisture surplus. If it cannot infiltrate into the soil it will
run over the surface as overland flow.
When evapotranspiration is greater than precipitation there is a reduction in the
amount of water stored with the soil - soil moisture utilisation. The amounted
of water stored in soil is also been reduced because some of the water is been
transferred as throughflow to the river.
Eventually all the available water stored in the soil will have been used up – soil
moisture deficit.