The analysis is the same as that used in HEC-18. It uses an equivalent pier width with a projected area the same as the total projection area of the piles. The basic pier scour equation applies. If debris is not considered, and if the multiple columns are spaced 5 diameters or greater apart, the maximum scour depth is limited to 1.2 times that for local scour of a single column (pile). Note, when the attack angle exceeds 5 degrees, the nose shape of the column will no longer affect the scour and K1 will be adjusted to 1.0. Since the attack angle is already accounted in the equivalent pier width, K2 will also be assigned a value of 1.