Pier scour in clear water for sediment mixtures

The current pier scour design in the USA is mainly based on the CSU equation, yet a recent incisive evaluation indicates a need to change it because substantial advances were made in the last two decades for understanding the pier scour processes. The objective of this research is then to propose a simplified scour mechanism and a physically-based scour depth equation for practical design purposes. A critical review on selected previous studies is first made to form the basis of this research. A simplified scour mechanism is next proposed in terms of the pressure gradient through flow-structure, flow-sediment and sediment-structure interactions. A hypothesis on the equilibrium scour depth equation is then proposed based on the understanding of the scour mechanism and tested by flume data. Finally, the proposed scour depth equation provides a criterion and a rule of thumb for scour design and evaluation.