Q$4.$ A bridge is placed in a long rectangular channel. The channel width upstream $($u$/$s$)$ and downstream $($d$/$s$)$ form the bridge is B $=3\mathrm{.}5$m$.$ The flow rate in the channel is $75$M$^3/$s$.$ the channel bed slope is $1\%,$ and the Manning roughness coefficient is n$=0\mathrm{.}012,$

$1.$ What is the critical depth u$/$s from the bridge?

$2.$ What is the u$/$s channel$$s normal depth? Is it subcritical or supercritical flow?