Hydraulics over a weir
This clip shows basic hydraulics over a weir with a small amount of plastic media in the flume. At the clip beginning dye is injected into flow upstream of the weir to show the transition from relatively deep, low velocity subcritical flow to critical and supercritical flow over the weir.
Downstream of the weir, supercritical flow is much faster and shallower. As the downstream gate is closed, stage rises and a submerged hydraulic jump appears downstream. Here we can also see the loss of energy due to the jump by comparing the elevation of the water surface below the weir with that above the weir. This energy loss is one of the things that make grade control structures work—they act to dissipate the energy of flow at a point of our choosing.
Note the turbulence and reverse roller (the sort that is very dangerous to be caught in) below the weir.
File 19076 is a 2.8MB Flash Video
Uploaded: Dec21 09
Last Modified: 2010-05-19 21:06:26