a dam resisting the pressure of impounded water by an arch principle, especially a dam having in plan the form of a single arch abutted by natural rock formations.
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British Dictionary definitions for arch dam
a dam that is curved in the horizontal plane and usually built of concrete, in which the horizontal thrust is taken by abutments in the sides of a valley. Arch dams must be built on solid rock, as a yielding material would cause a failure
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012