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Hydrologic Cycle
Groundwater is a component of the hydrologic
cycle. In simple terms, water or one of its forms-water vapor
and ice-can be found at the earth's surface, in the atmosphere,
or beneath the earth's surface. The hydrologic cycle has no beginning
or ending location; however, it is often thought of as beginning
in the oceans. Water evaporates from a surface water source such
as an ocean, lake, or through transpiration from plants. The water
vapor may move over the land and condense to form clouds, allowing
the water to return to the earth's surface as precipitation (rain
or snow). Some of the snow will end up in polar ice caps or in glaciers.
Most of the rain and snowmelt will either become overland flow
in channels or will infiltrate into the subsurface. Some of the
infiltrated water will be transpired by plants and returned to the
atmosphere, while some will cling to particles surrounding the pore
spaces in the subsurface, remaining in the unsaturated zone. The
rest of the infiltrated water will move gradually, driven by gravity,
into the saturated zone of
the subsurface, becoming groundwater. From here, groundwater will
flow toward points of discharge such as rivers, lakes, or the ocean
to begin the cycle anew.
For a list of common groundwater terms, go to the Groundwater
Glossary.
Groundwater in California
Most of California's groundwater occurs in material deposited by
streams, called alluvium. Alluvium consists of coarse deposits,
such as sand and gravel, and finer-grained deposits such as clay
and silt. In an alluvial environment, the coarse materials such
as sand and gravel deposits usually provide the best source of water
and are termed aquifers; whereas, the finer-grained clay and silt
deposits are relatively poor sources of water and are referred to
as aquitards. California's groundwater basins usually include one
or a series of alluvial aquifers with intermingled aquitards. Although
alluvial aquifers are most common in California, other groundwater
development occurs in fractured crystalline rocks, fractured volcanics,
and limestones.
Other interesting Groundwater Materials
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