4. Sedimentology and Stratigraphy

Sediment Transport — Quiz

Test your understanding of sediment transport with 5 practice questions.

Practice Questions

Question 1

Using Stokes’ law, calculate the settling velocity $w_s$ of a spherical particle of diameter $D=0.2\,\mathrm{mm}$, particle density $\rho_s=2650\,\mathrm{kg/m^3}$, fluid density $\rho=1000\,\mathrm{kg/m^3}$, dynamic viscosity $\mu=1.0\times10^{-3}\,\mathrm{Pa\cdot s}$, and $g=9.81\,\mathrm{m/s^2}$. The formula is $w_s=\frac{(\rho_s-\rho)gD^2}{18\mu}$.

Question 2

For sediment of diameter $D=0.25\,\mathrm{mm}$, critical Shields parameter $\theta_c=0.05$, particle density $\rho_s=2650\,\mathrm{kg/m^3}$, fluid density $\rho=1000\,\mathrm{kg/m^3}$, and $g=9.81\,\mathrm{m/s^2}$, what is the critical bed shear stress $\tau_c$? Use $\tau_c=\theta_c(\rho_s-\rho)gD$.

Question 3

For a particle with settling velocity $w_s=0.036\,\mathrm{m/s}$, friction velocity $u_*=0.05\,\mathrm{m/s}$, and von Kármán constant $\kappa=0.4$, what is the Rouse number $P=\frac{w_s}{\kappa u_*}$ and the dominant transport mode if particles remain in suspension for $P<2.5$?

Question 4

In uniform open‐channel flow with fluid density $\rho=1000\,\mathrm{kg/m^3}$, gravitational acceleration $g=9.81\,\mathrm{m/s^2}$, hydraulic radius $R=2.0\,\mathrm{m}$, and slope $S=0.005$, what is the bed shear stress $\tau_b$? Use $\tau_b=\rho gRS$.

Question 5

According to Shields’ analysis, for a sediment grain at entrainment threshold, which fluid force components must exceed the opposing forces?