Hydraulic jump

A hydraulic jump in the river

A hydraulic jump is a discrepancy in water levels. When water in a stream flows over a rock, the water may reach supercritical speed - that is, the speed of the water may exceed the speed that waves propagate at. If so, there will be a sudden change in the water's height so that the speed of the water is reduced to subcritical speed.

The equation that governs this phenomena is:

$H_{2}/H_{1}=1/2(<sqrt>8(F_{1})^{2}+1</sqrt>-1)$

where $F_{1}=<sqrt>gY_{1}</sqrt>$ F_1 is called the Froude number, g is the acceleration due to gravity, and Y_1 is the depth of the water.