1. In open channel flow, a manufactured conduit (usually rectangular in shape) with a portion having a constricted cross section, which may be used to control and measure streamflow. 2. In geomorphology, a narrow, steep-sided valley. 3. In hydraulics, a channel used for studying the flow of fluids under gravity. The fluid is pumped from a sump to a stilling tank that acts as a reservoir from which the fluid is discharged down the flume at varying speeds. The motion is viewed from above or through glass sides.