Effect of low tailwater during drought on scour conditions downstream of an ogee spillway

Low tailwater stages downstream of the stilling basin of an ogee spillway as a result of drought conditions can result in swept-out hydraulic jumps that enhance scour potential downstream of the structure. A hydraulic model study was conducted to assess the impact of low tailwater on energy dissipation provided by the stilling basin and the stability of the revetment lining in the downstream stilling pool. Detailed velocity and turbulence profiles were measured in the stilling pool for both submerged and swept-out hydraulic jumps. The results suggest that the primary scouring mechanism may be the impact of a submerged jet on the bed.