Visualization Tests on Scour Rates below Pipelines in Steady Currents.

This paper presents visible experimental results of three-dimensional scour beneath pipelines. A miniature camera installed inside a transparent pipeline was used to observe the scour propagation process under a pipeline in steady currents. The data showed that the average scour hole propagation rate decreased nonlinearly with increasing pipeline embedment. The scour propagation rate increased with the Froude number at an increasing climb rate. The critical flow velocity for scour propagation was investigated. The critical velocity increased with increased pipeline embedment and the flow depth. It was lower than the critical velocity of sediment incipient motion. An empirical equation for the variation of the Froude number with the scour propagation rate was proposed for pipeline embedment ratios 0.045 = e=D = 0.1 and relative flow depths 2.73 = y0=D = 4.08. [ABSTRACT FROM AUTHOR]