For a wide river with a depth $=5$m and an EGL $=3$ x $10-4$ and a d$50=1\mathrm{.}5$mm$.$

a$.$ Find the critical bed shear stress $()$ and the critical shear velocity $$

corresponding to density $2650$ kg$/$m$3$

$.$

b$.$ Determine the excess shear stress on the bed.