siphon

Closed conduit, a portion of which lies above the hydraulic grade line. This results in a pressure less than atmospheric in that portion and hence requires that a partial vacuum be created to start flow. A siphon utilizes atmospheric pressure to effect or increase the flow of water it carries. It may occur naturally in karstic regions.

 

Source:

UNESCO/WMO International Glossary of Hydrology (2nd revised ed., 1992)

Posted on February 24, 2014 .