Backward Flow Velocities of Submerged Hydraulic Jumps

This paper describes an experimental investigation of submerged hydraulic jumps forming downstream of overflow structures. Submergence happens when the hydrological tailwater depth in a channel exceeds the jumpʹs subcritical sequent depth. It is a common occurrence, particularly with low overflow structures. The jump may produce a vortex having significant countercurrent free-surface velocities. This phenomenon is held responsible for frequent personal injury accidents of unwary recreationists, hence its appellation of "drowning machine." Experimental results, supported by analytical reasoning, are presented that quantify these dangerously high velocities for all hydraulic situations.