Scour by jets, at high-head structures and at culvert outlets

Flows through hydraulic structures often issue in the form of jets. The velocities are usually high enough for these jets to produce sizable, even dangerous scour holes. Fully submerged jets, both plane or two-dimensional and circular are characterized by a linear increase in width and a Gaussian velocity distribution in the fully developed part of the jet. Aeration of the jet during its flight in air can also affect the jet velocity, but E. Häusler assumed that for conventional design values, the core region will persist throughout the drop to the tailwater level. Data on scour have generally been obtained from small scale tests with non-cohesive material or from field observations for which the material properties are unspecified. In conclusion: the available relations give an indication of scour to be expected in coarse non-cohesive material or fissured rock.