Clear-water abutment scour prediction for simple and complex channels.

One hundred and sixty-one laboratory and one field clear-water abutment scour data sets were regressed using a Box-Tidwell power transformation procedure. The predictive equation was verified using additional laboratory data for compound channels. A momentum ratio term was used to account for flow redistribution, differences in overbank geometries, and scale sizes. The regression identified the most applicable and dominant independent variables that affect the magnitude of clear-water abutment scour. The resulting equation has a significantly lower standard error of estimate than previously published equations. This formulation is more robust and accurately predicted abutment scour depth at both laboratory and prototype scale. With additional refinement, improved abutment scour predictive equations can be realized by using alternative regression procedures and including the momentum ratio to buffer the effect of abutment length at large prototype scales.