Mike Zeller, who developed this equation stresses that the bend scour version only includes general and bend scour, and that a full scour analysis requires a careful assessment of other processes including contraction, low flow, and bed form effects (Tetra Tech, 2009).


Excerpts from Revised Updated Scour Guidelines.pdf

The Zeller Bend Scour Equation Includes General Scour: Don't Double Count

The Zeller "Bend Scour" equation includes general AND Bend Scour.  The general scour equation is just the original equation with the bend component extracted.  Do not add the bend and general scour results, it will double count general scour. 


The primary source for the implemented equation is Simons and Li (1985)

Simon_Li_1985_ADWR_Engineering_Analysis_Fluvial_Systems.pdf

These were propagated by Baird et al (2019) who broke the equation into general scour and bend scour versions.  The "bend scour" equation includes both bend and general scour,