Context: Spillways release massive volumes of water from high elevations.

Application: As water rushes down a spillway, it achieves highly supercritical velocities, carrying tremendous kinetic energy. If this flow enters the natural riverbed unmodified, it will scour the foundation and potentially undermine the dam. Engineers design stilling basins at the toe of the spillway. These basins force a hydraulic jump to occur by creating a deep tailwater pool. The jump violently converts the kinetic energy into turbulence and heat (head loss), ensuring the water exits into the river at a safe, subcritical velocity.

Context: Constructing a weir or dam alters the water surface profile for miles upstream.

Application: When a weir is placed in a subcritical stream (mild slope), it creates an M1 water surface profile (a backwater curve). The depth increases from normal depth far upstream to the critical depth passing over the weir. This artificial deepening reduces flow velocity, causing sediments to drop out of suspension and deposit in the reservoir. Engineers use the Standard Step Method to precisely model this M1 curve to determine the extent of flooding and the land area that will be permanently inundated.