Scouring due to submerged sills

Abstract

As the construction of infrastructure in and around a river channel modifies the flow and sediment transport characteristics, prediction of scour depths is an integral part of engineering design. Whilst there are a substantial number of predictive equations available to estimate the scour resulting from bridge piers, other types of structures have been less examined. This paper reports on flume experiments and numerical modelling to examine the role of submerged sills in the development of scour. Sills can be utilised in a channel to control bed stability, influence mixing dynamics or dictate water levels. Additionally, sills can occur due to infrastructure including riprap-covered pipeline crossings. The majority of previous work on sills has been undertaken on unsubmerged or partially submerged sills. The only experimental work on submerged sills is restricted to a range of conditions not applicable to pipeline crossings in large sand-bed rivers. This paper presents experiments, using artificial light-weight sediment (crushed walnut shell), undertaken with a fixed flow depth but a range of velocities and sill heights, all of which are in the surface flow regime. Hydrodynamic numerical simulations were run for the same conditions to gain insight into the corresponding flow structure.