  We present a continuum approach to model segregation of size-bidisperse
granular materials in unsteady bounded heap flow as a prototype for modeling
segregation in other time varying flows. In experiments, a periodically
modulated feed rate produces stratified segregation like that which occurs due
to intermittent avalanching, except with greater layer-uniformity and higher
average feed rates. Using an advection-diffusion-segregation equation and
characterizing transient changes in deposition and erosion after a feed rate
change, we model stratification for varying feed rates and periods. Feed rate
modulation in heap flows can create well-segregated layers, which effectively
mix the deposited material normal to the free surface at lengths greater than
the combined layer-thickness. This mitigates the strong streamwise segregation
that would otherwise occur at larger particle-size ratios and equivalent steady
feed rates and can significantly reduce concentration variation during hopper
discharge. Coupling segregation, deposition and erosion is challenging but has
many potential applications.
