Experimental study of local scour around submerged square piles in combined waves and current

Scour around submerged square piles in combined waves and current has rarely been investigated. In this study, experimental tests in current-only conditions were performed with several pile height-to-width ratios at an almost fixed flow intensity. Codirectional regular waves corresponding to various Keulegan–Carpenter (KC) numbers were individually superimposed on the current. Temporal scour depth and sand bed profile evolutions in the pile vicinity were studied by comparing scouring tests in current-only conditions with waves-current conditions. The results indicated that the pile height-to-width ratio had an important effect on the scour depth. The sediment scour rate was controlled by the flow intensity in the initial scouring stage. The scouring duration needed for the equilibrium state in waves-current scour was much smaller than that in current-only conditions owing to the sediment backfilling induced by sand ripples in the developing scouring stage. More accurate relationships between the equilibrium scouring depth and KC values were obtained by fixing the relative current velocity (Ucw) at approximately 0.54.