Local scour due to sediment-carrying free-overfall water jet

Abstract

Results are presented of 80 experiments on the time variation of scour in uniform bed materials due to a sedimentladen free-overfall jet. It was found that the scour hole characteristics (i.e. the depth of scour, the width of the scour hole, the length of the scour hole and the height of the ridge formed downstream of the scour hole) are functions of the densimetric Froude number, the ratio of drop height to tailwater depth, the ratio of drop height to hydraulic radius of jet, sediment number, and the non-dimensional development time. The influences of different parameters on the longitudinal and lateral profiles of the scoured bed are investigated. Increasing the sediment load in the water jet leads to a decrease in the dimensions of the scour hole. Scour profiles at different times are geometrically similar, and can be expressed by a polynomial using relevant parameters. New empirical equations for the prediction of developing scour-hole geometry and downstream ridge height are presented.