Inclined-bed sediment threshold
= Inclined-bed sediment threshold
For locally bed-tangent <drag force> and an upslope angle $a$, a spherical-grain <force balance> gives $\tau_{\mathrm{th}}(a)=\tau_{\mathrm{th},0}(\cos a+\sin a/\mu_s)$. The small-slope term is $\delta\tau_{\mathrm{th}}=(\tau_{\mathrm{th},0}/\mu_s)\eta_x$. A horizontal <drag force> instead changes the normal contact <force> and gives a different slope correction.