Throughflow
Encyclopedia
In hydrology
Hydrology
Hydrology is the study of the movement, distribution, and quality of water on Earth and other planets, including the hydrologic cycle, water resources and environmental watershed sustainability...

, throughflow is the horizontal movement of water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 in the soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...

 zone. This type of flow must first emerge on land before it enters a body of surface water (stream, lake, pond) to be considered throughflow (as opposed to interflow
Interflow
In hydrology, interflow is the lateral movement of water that occurs in the upper part of the unsaturated zone, or vadose zone, that directly enters a stream channel or other body of water without having occurred first as surface runoff ....

 where the flow enters directly the body of surface water without having first emerged at the surface). Once water infiltrates the soil, it moves downwards under gravity and, because the soil becomes more compact and less permeable with increasing depth, will begin to move sideways at speeds of between 0.005 to 0.3 m/h. Throughflow usually happens when the soil is completely saturated with water. This water then flows underground until it reaches a river, lake, or ocean. The lowest rates of flow occur in heavy clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...

 soils.

Throughflow should not be confused with throughfall
Throughfall
In Hydrology, throughfall is the process which describes how wet leaves shed excess water onto the ground surface. These drops have an erosive power because they are larger than rain drops, however, if they travel a shorter distance their erosive power is reduced...

or ground-waterflow, which are other hydrological terms.
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