Local scouring downstream of a spillway with an apron

Local scour downstream of stilling basins constitutes an important field of research in the context of the stability of hydraulic structures. This paper deals with the temporal and spatial evolution of local scour downstream of low-head spillways with a horizontal apron. Experiments were carried out in a 1 m wide and 20 m long rectangular channel. Three different, nearly uniform, sediments were used for the mobile bed. Tests were of long duration from 48 up to 196 h, but a few runs of short duration (1 or 3 h) were also carried out to better analyse the earlier scour stages. It was found that the main dimensionless parameters governing the scouring process are the tailwater densimetric Froude number, the relative time, and the relative distance of the toe of the hydraulic jump from the apron edge. Based on the experimental data, the salient features of the local bed morphology evolution are described through simple power-type equations. No experimental evidence was found in support of the similarity of scour profiles.