A concrete $($n $=0\mathrm{.}013)$ triangular channel, laid at a longitudinal slope of $0\mathrm{.}0009$mlm$,$ hasthe side slopes of $2$H:$1$V$.$ If the uniform flow rate through the channel is $0\mathrm{.}5$ ms$,$ determine whether the flow in the channel is sub$-$critical, critical or super$-$critical?Justify your answer using appropriate hydraulics principles.