As can often be seen in a kitchen sink when the faucet is running, a high-speed channel flow (v1, h1) may ''jump'' to a low-speed, low-energy condition (v2, h2).
The pressure at sections 1 and 2 is approximately hydrostatic, and wall friction is negligible. Use the continuity and momentum relations to find h2 and v2 in terms of (h1, v1).
