A horizontal, rectangular channel is $5$ m wide and flows at $4$ m$/$s with a water depth of $5$ m$.$ The energy$-$depth diagram $($y versus E curve$)$ is shown in Figure $1.$ The flow encounters a sudden step. Assuming there are no losses at the transition, answer the following: $1.$ What is the critical depth? $2.$ Is the flow upstream of the step subcritical, critical, or supercritical? $3.$ If there is a $0\mathrm{.}25$ m sudden drop in the channel bottom, what will be the downstream water depth?