Backward flow velocities of submerged hydraulic jumps

This paper describes an experimental investigation of submerged hydraulic j umps forming downstream of overflow structures. Submergence happens when th e hydrological tailwater depth in a channel exceeds the jump's subcritical sequent depth. It is a common occurrence, particularly with low overflow st ructures. The jump may produce a vortex having significant countercurrent f ree-surface velocities. This phenomenon is held responsible for frequent pe rsonal 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 hyd raulic situations.