- When equation (15) is applied to rivers in flood the value of R gives the normal depth of scour. Hence this formula is very useful in determining the levels of foundations, vertical cutoffs etc. This formula is popularly called Lacey's scour depth formula.- Lacey's regime scours depth is given by. Where q is discharged per unit width and f is silt factor.- According to Lacey, the depth of scour in a river depends upon the straightness of the reach. If D is the depth of scour in regime flow in a right-angled bend, it is 2.00 D