The top flow line of a saturated soil mass below which seepage takes place, is called the Phreatic line.
Hydrostatic pressure acts below the phreatic line whereas atmospheric pressure exists above the phreatic line. This line separates a saturated soil mass from an unsaturated soil mass. It is not an equipotential line, but a flow line.
For an earthen dam, the phreatic line approximately assumes the shape of a parabola.
See also
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Phreatic
''Phreatic'' is a term used in hydrology to refer to aquifers, in speleology to refer to cave passages, and in volcanology to refer to a type of volcanic eruption.
Hydrology
The term phreatic (the word originates from the Greek , meaning "well" ...
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Embankment dam
References
Hydrology
Dams
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