A hydraulic jump is formed between a sluice gate (upstream) and a weir (downstream) explain, with an appropriate plot, what happens if the gate opening is reduced.
"(Begin by drawing generic E-y and M-y curves beside each other).
Because this is a hydraulic jump situation, we know that the flow regime of the water through the sluice gate is super-critical. Before the opening is reduced, we have E1 (as shown on the diagram) occurring after the sluice gate, corresponding to the momentum of M1, which is conserved through the jump. The change in depths before and after the jump can be determined by finding y values at M1 from the momentum curve.
When the gate opening is reduced, the depth of flow out of the opening is also reduced. Referring back to our Energy curve, we now have E2 occurring at a shallower depth and thus a greater specific energy than E1. The corresponding momentum M2 is also greater than M1. The y values that occur at M2 can now be used to determine the new change in depths before and after the jump. As you can see, decreasing the gate opening will cause the overall change in depth through the jump will to be greater, meaning that more energy will be lost. "