Drainage Basin Key Terms

The process by which liquid water is transferred to water vapour. This requires a large amount of energy, usually provided by the heat of the sun.

Total amount of water removed by evaporation and transpiration form a vegetated land surface. Transpiration specifically refers to water lost through the stomata in the leaves of a plant.

The slowest transfer of water within a drainage basin, which provides the main imput of water into a river during drought. Groundwater flows at a slow but steady rate through bands of sedimentary rock. It can take thousands of years for moisture that seeps into permeable rocks under the surface to be returned to the drainage basin hydrological cycle as groundwater flow.

The passage of water into the soil. It takes place fairly quickly at the start of a storm, but as the soil becomes saturated, the rate of infiltration falls rapidly. The rates of infiltration are affected by the nature of the soil itself, for example sandy soil lets more water infiltrate through than clay soils.

The process by which raindrops are directly prevented from reaching the surface of the soil by trees (leaves, branches and stems) and also herbaceous plants and grasses which grow close to the surface. Evaporation then removes some of the moisture from the system and does not reach the river as runoff.

The downward movement of water within the rock under the soil surface. The rate depends on the rock type. Igneous or metamorphic rocks, for example, are often impermeable so there is no percolation or groundwater flow.

Water of any kind that falls from the atmosphere to the surface of the earth e.g. rain, sleet, snow, hail.

All water that enters a river and eventually flows out of the drainage basin. It can be quantified by measuring the discharge of a river.

The water that runs down the stems and branches of plants and trees during and after rain in order to reach the ground. It takes place after interception has occurred.

The water that drips off leaves during a rainstorm. It occurs when more water falls onto the interception layer of a tree canopy than can remain on the leaves.

The water that moves down-slope through the subsoil, pulled by gravity. It is very effective when impermeable rock prevents percolation.