Water Balance

Year 12 geography GCE

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.

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.