FLUME EXPERIMENTS ON ABUTMENT SCOUR: CONFRONTING COMPLEXITIES IN PROCESS AND SIMILITUDE

The paper addresses the extensive complexities confronting laboratory flume experiments on scour at bridge abutments. The complexities complicate the development of reliable scour-prediction relationships, and in a practical sense imply that such relationships can only be of approximate accuracy. The complexities stem from the nature of the approach flow-field, the soil and sediment conditions at typical abutments, and thereby from the mix of scour and slope-stability failure processes potentially at play in the vicinity of bridge abutments. The full set of failure processes has yet to be determined and documented, and inevitably entails extensive investigative experiments using laboratory flumes. However, flume experiments on abutment scour are fraught with their own significant complexities of process and similitude; some failure processes are difficult to replicate directly in flumes, and certain scale effects prevail. Arguably, the mix of complexities has muddled perceptions of scour extents observed at bridge sites. The paper attempts to somewhat clarify the muddle, and it floats for comment a plan for flume experiments aimed at addressing, and working around, the complexities.