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In a bidisperse particle suspension transported by a steady depositing gravity current, species with concentrations $c_i$ and downward settling velocity magnitudes $v_i$ satisfy $c_i(x)=c_{i0}{e}^{-v_{i}x/q}$. Their local particle deposition fluxes are $v_i{c}_i$. The local deposited particle-volume fraction belonging to species one isFor $v_1>v_2>0$ and both species present, $f_1$ decreases strictly downstream, since $f_1^{\prime }=(v_2-v_1)f_1(1-f_1)/q$. If $g_i^{\prime }=g_{0i}{c}_i$, use $c_i=g_i^{\prime }/g_{0i}$ rather than buoyancy ratios unless $g_{01}=g_{02}$. A number fraction additionally divides each species volume flux by its single-particle volume. Integrating deposition over $[0,x]$ instead gives cumulative weights $q{c}_{i0}(1-e^{-v_{i}x/q})$.

Consider a column $0<z<H$ initially filled with a uniform bidisperse particle suspension. In an independent-settling idealization, normalized concentrations $q_i$ obey fluxes $j_i=-W_i{q}_i(1-q_i)$, with $W_i>0$. A stationary packed deposit has fractions $p_1+p_2=1$. The deposit composition from sedimentation jump conditions determines its upward front speed $s$ and the fractions $p_i$.

Suppose species 1 has the faster downward clearing front: $v_1=W_1(1-q_1)>v_2=W_2(1-q_2)$. Before interaction, the fast clearing front is at $H-v_{1}t$, while the deposit front is at $st$. They first meet atAll species 1 has then entered the earlier mixed deposit. Above it, only species 2 remains suspended; its later sedimentation shock adds a pure-species-2 layer. Separate particle-volume conservation laws giveHere $h_2$ is the final pure-species-2 layer thickness. This two-stage picture follows from the stated independent fluxes and packed stationary branch; general coupled hindered settling can have a different wave structure.