What is the most important job of a hydraulic jump when water flows out of a dam's spillway?

When water flows out of a dam's spillway, it accelerates to very high velocities, resulting in a condition known as supercritical flow. Supercritical flow describes water that is moving so rapidly and is relatively shallow, characterized by a Froude number greater than one, where the inertial forces are dominant over gravitational forces. This high-velocity flow carries a substantial amount of kinetic energy, which is the energy of motion. If this water with high kinetic energy were allowed to flow directly into the natural river channel below the dam, it would cause severe erosion and scouring of the riverbed and banks. Erosion is the process of wearing away earth material, and scouring is a specific form of erosion caused by the abrasive action of moving water, which could destabilize the downstream environment and even undermine the dam's foundation. The most important job of a hydraulic jump in this scenario is to dissipate a large portion of this destructive kinetic energy. A hydraulic jump is a natural phenomenon, often engineered to occur in a specific structure called a stilling basin immediately downstream of the spillway, where there is an abrupt, turbulent transition from high-velocity, shallow (supercritical) flow to lower-velocity, deeper (subcritical) flow. Subcritical flow is characterized by a Froude number less than one, meaning gravitational forces are more dominant, and the flow is slower and deeper. During the hydraulic jump, intense turbulence, violent mixing, and the formation of large rollers within the water body convert the excessive kinetic energy into less harmful forms, primarily heat and sound. This process significantly reduces the water's velocity before it enters the natural river channel, thereby preventing severe erosion and scour, and safeguarding the dam's integrity and the downstream ecosystem.