Thalweg
Black's Law Dictionary · Henry Campbell Black, M.A. · 1910
Black's Law Dictionary
Germ. A term used in topography to designate a line representing the deepest part of a continuous depression in the surface, such as a watercourse; hence the middle of the deepest part of the channel of a river or other, streain.
See Iowa v. Illinois, 147 U. S. 1, 13 Sup. Ch 239, 37 L. Ed. 55; Keokuk & H. Bridge Co. v. People, 145 HI. 596, 34 N. E. 482.