Temporal Variation of Live-Bed Pier Scour under Combined Wave-Current Flow in a Large-Scale Flume

摘要

Studies on the temporal variation of live-bed scour under waves alone and combined wave-current flow are not as extensive as those under current-alone conditions. Motivated by this, series of experimental tests were carried out in a large-scale flume (5 m wide, 8 m deep, and 450 m long). The scour processes in different locations of the scour hole were monitored simultaneously during the tests. Measured data indicated that the scour depth versus time can be expressed by an exponential equation for both waves-only and combined wave-current conditions. A piecewise equation for predicting the characteristic timescale under combined wave-current flow is proposed based on the data from the literature and the present experiment. In live-bed scour, the effect of wave-generated ripples on scour depth fluctuation could be ignored under waves alone. For the combined wave-current flow, the fluctuation amplitude of scour depth was approximately equal to the height of bed forms under current-dominated conditions and nearly half of the observed height of the bed forms in wave-dominated conditions.