Prediction of Scour Formation Due to a Turbulent Wall Jet Along a Non-Cohesive Sediment Bed. (Paperback)

Scour in non-cohesive sediment beds is a concern in engineering projects such as dam spillways and shallow maritime navigation locations. Significant scour can lead to undermining of hydraulic structures and altered boundary flow along the bed. Research has been undertaken to advance the current state of knowledge regarding scour due to planar wall jets. Experiments presented here also investigate the flexibility and suitability of Particle Image Velocimetry (PIV) for other sediment transport applications. Improved scour prediction methods are developed by utilizing state-of-the-art experimental techniques. Experiments are carried out over a range of particle sizes (0.200--0.750 mm) and Reynolds numbers (2,222--7,777). Incremental scour data is collected by profile plotting and centerline scour measurements. Measurements reveal a bedform that is nearly self-similar. From the dimensionless self-similar scour profiles, rigid boundary sediment beds are constructed so that the flow along the scour profile could be analyzed. Flow characteristics including velocity fields and boundary layers along the scour profile are obtained with PIV. Research indicates a strong correlation of the measured velocity fields with results from previous researchers. From the PIV acquired data, the boundary shear stress is calculated using a quadratic friction law. Predictions of scour profile equilibrium are performed by equating the jet induced boundary shear to the slope corrected critical shear. A scour evolution model is developed based on established sediment transport formulae. Scour prediction models are validated with data collected from laboratory experiments. Results indicate that existing sediment transport equations over-predict scouring rates. In addition to long term scouring, PIV technology is implemented to study the rapidly evolving early stages of scour. PIV provides a non-intrusive, near-instantaneous technique for data collection. Results from early stage live-bed scour experiments indicate scour growth is linearly related to the logarithm of time. This is in agreement with the long-term scour profile data collection. In addition, cyclic "digging and filling" cycles are observed during the early stages of scour.