AN OVERVIEW OF SCOUR TYPES AND SCOUR-ESTIMATION DIFFICULTIES FACED AT BRIDGE ABUTMENTS

Complex hydraulic engineering problems are faced when assessing the likelihood of scour of alluvial channels at bridge crossings. These problems are particularly complex in the vicinity of bridge abutments located in compound channels. In this paper, the range of scour types that may occur at bridge abutments is described and the extensive attendant difficulties confronting accurate estimation of abutment-scour depth are discussed. The difficulties, which include similitude aspects of laboratory experiments on scour at bridge abutments, complicate the development of reliable scour-estimation relationships. The relationships and guidelines currently available do not adequately take into account the complexities of channel morphology and sediment/soil disposition. The difficulties imply that estimation relationships can only be of approximate accuracy, whereby bridge designers may estimate reasonable upper-bound extents of scour produced by overall general conditions of scour. Extensive investigative experiments using laboratory flumes are proposed to investigate several general, though simplified, conditions of scour at abutments. The experiments confront some scour complexities (such as influence of similitude) and sidestep others, such as slope stability.