Analysis of scour due to breaking and non-breaking waves around a group of vertical piles in the field

A study was carried out on the scour around groups of piles in the field exposed to breaking and non-breaking waves. The pile groups located in the surf zone were affected by mean currents generated by breaking waves. The main purpose of this study was to derive simple predictive formulas for the geometric propel-ties of the scour hole in terms of non-dimensional parameters describing the flow (waves and current), sediment, and pile characteristics. A comprehensive data set from the Pacific coast of Japan was employed where the beach profile along a pier experiencing scour around its piles was surveyed every week. Detailed wave measurements were available and pile groups exposed to breaking and non-breaking (oscillatory) waves were investigated separately. The maximum scour depth for non-breaking waves showed a distinct correlation with the Keulegan-Carpenter (KC) number and an empirical relationship derived agreed with some earlier laboratory experiments, if an equivalent diameter was defined for the pile groups. The scour depth under breaking waves displayed considerable scatter when related to the KC number showing better correlation with the longshore current normalized by the near-bottom wave orbital velocity.