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Wednesday, January 26, 2011

Water cycle

Water Cycle

The hydrosphere – the surface and near-surface waters of the Earth – is made of meteoric water.The water cycle is the circulation of meteoric water through the hydrosphere, atmosphere, and upper parts of the crust. It is linked to the circulation of deep-seated juvenile water associated with magma production and the rock cycle. Juvenile water ascends from deep rock layers through volcanoes, where it issues into the meteoric zone for the first time. On the other hand, meteoric water held in hydrous minerals and pore spaces in sediments, known as connate water, may be removed from the meteoric cycle at subduction sites, where it is carried deep inside the Earth.

The land phase of the water cycle is of special interest to geomorphologists. It sees water transferred from the atmosphere to the land and then from the land back to the atmosphere and to the sea. It includes a surface drainage system and a subsurface drainage system. Water flowing within these drainage systems tends to be organized within drainage basins, which are also called watersheds in the USA and catchments in the UK. The basin water system may be viewed as a set of water stores that receive inputs from the atmosphere and deep inflow from deep groundwater storage, that lose outputs through evaporation and streamflow and deep outflow, and that are linked by internal flows. In summary, the basin water runs like this. 

Precipitation entering the system is stored on the soil or rock surface, or is intercepted by vegetation and stored there, or falls directly into a stream channel. From the vegetation it runs down branches and trunks (stemflow), or drips off leaves and branches (leaf and stem drip), or it is evaporated. From the soil or rock surface, it flows over the surface (overland flow), infiltrates the soil or rock, or evaporates. Once in the rock or soil, water may move laterally down hillsides
(throughflow, pipeflow, interflow) to feed rivers, or it may move downwards to recharge groundwater storage, or it may evaporate.Groundwater may rise by capillary action to top up the rock and soil water stores, or it may flow into a stream (baseflow), or may exchange water with
deep storage. 

Sources : Gerrard, John.2007.FUNDAMENTALS OF GEOMORPHOLOGY. New York : Routledge 270 Madison Avenue

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