Scour downstream of unsubmerged non-full flowing trapezoidal culvert outlet

Abstract

In this project, the study of local scour downstream of non-full flowing trapezoidal culvert outlet is presented; to understand and investigate the geometry of scour hole below the culvert outlet at equilibrium scour conditions due to the phenomenon of scouring. Four series of laboratory experiments were run, by varying the tailwater depths and the flowrates.

The effects of scour can be seen when water is channel from a reservoir through a trapezoidal culvert outlet leading to a clear water scour. The study was done with a uniform sediment bed under the influence of the sediment size and tailwater depth. Experiments were conducted with both increasing the flowrate and tailwater depths.

Dimensionless analysis was used to further explain the magnitude of scouring caused by local scour downstream of non-full flowing trapezoidal culvert outlet. It was shown that scour geometry is a function of tailwater depth, H, the ratio of the equilibrium maximum scour depth to hydraulic radius of the channel outlet ( d_se)/R_h , and the Densimetric Froude number, Fo.

Empirical relationship between the equilibrium maximum scour width, Wse, length, Lse , and volume, Vse, with the maximum scour depth, dse, of the scour holes, have also been proposed.

Unsubmerged non-full flowing culvert outlet was also found to scour less than unsubmerged full flowing outlets regardless of the shapes of culvert outlets. Hence, this indicates that the culvert shape does have an impact on the scour hole geometry