Trough

A long, hollow vessel, generally for holding water or other liquid, especially one formed by excavating a log longitudinally on one side; a long tray; also, a wooden channel for conveying water, as to a mill wheel.

Any channel, receptacle, or depression, of a long and narrow shape; as, trough between two ridges, etc.

a narrow depression (as in the earth or between ocean waves or in the ocean bed)