Ackers and White (1973) is a total load function, developed from flume data for relatively uniform gradations ranging from sand to fine gravels. Ackers and White derived the equation dimensional analysis and did not include a grain shear partition. They fit coefficients to the equation based on experiments that included a range of bed configurations including ripples, dunes, and plane bed conditions.
This function does not have an intuitive shear stress, excess shear stress, or excess stream power formulation that drives most of the other equations. But it is built on a very similar excess "mobility" power function. The sediment flux is a function of a "Transport Parameter": Which is just a simple, dimensionless, power function, of excess "Mobily" with empirical coefficients and an empirical mobility threshold: HEC-RAS exposes the threshold mobility (A) and the coefficients (C and m) so users can calibrate them. However, these are not fixed parameters. They are dynamic, changing with sediment properties and flow. Molders who chose to calibrate Ackers-White should use scaling factors instead.
Mobility in this transport approach is a function of the Bagnold version of stream power (tV) where t is represented by u*):
