Scour in the transition from super- to subcritical flow without a hydraulic jump

Local scour in the transition from super- to sub-critical flow without a hydraulic jump is investigated based on model experimentation. Supercritical flow was enforced by a box-culvert, passed a curved bed, and then flowed over the sediment bed. The scour processes and the initiation of sediment motion are discussed. Attempts are also made to explain similarities among scour processes and profiles. The temporal development of the maximum scour depth is evaluated. Results indicate that the maximum equilibrium scour depth and scour hole geometry in the transition from super- to sub-critical flow without a hydraulic jump significantly depend on the upstream supercritical approach flow, and the densimetric Froude numbers. Scour profiles were also compared with those resulting from equivalent hydraulic jumps, indicating that the geometrical characteristics of the scour holes are significantly smaller than those of the corresponding hydraulic jumps. Finally, relationships characterizing the equilibrium scour hole geometry are derived based on the experimental results.