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Sediment Transport Hydraulics: Suspended Load Dynamics and the Rouse Profile Equation

Sediment carried in suspension by turbulent channel flow balances downward gravitational settling with upward turbulent diffusion. Under steady equilibrium conditions, this vertical mass exchange is governed by the convection-diffusion equation. Integrating this yields the Rouse Concentration Profile: $\frac{C_y}{C_a} = \left( \frac{h - y}{y} \cdot \frac{a}{h - a} \right)^{Z_{R}}$ ​Where $C_y$ is sediment concentration at height $y$ above the bed, $C_a$ is reference concentration at height $a$, and $h$ is total water depth. The non-dimensional Rouse Number $(Z_{R})$ determines the shape of the vertical sediment concentration curve: $Z_{R} = \frac{w_s}{\kappa \cdot u_*}$ ​Where $w_s$ is sediment particle settling velocity, $\kappa$ is von Kármán’s constant $(\approx 0.40)$, and $u_*$ is shear velocity $(u_* = \sqrt{g \cdot R \cdot S}).$ Higher Rouse numbers $(Z_R > 2.5)$ indicate that sediment transport is restricted primarily to near-bed bedload, while lower values $(Z_R < 0.8)$ ...