$4\mathrm{.}20.$ A mesuntain stream has boulders with a median size $($d$\_(50))$ of $0\mathrm{.}50$ ft $.$ The stream can

be considered approximately rectangular in shape and very wide, with a slope of $0\mathrm{.}01.$

You may assume that k$\_($s$)=2$d$\_(50).$

$($a$)$ For a discharge of $7\mathrm{.}0$cf$($s$)/($f$)$t$,$ calculate the normal depth and critical depth and

classify the slope as steep or mild.

$($b$)$ Discuss how a Manning's n that is variable with depth affects the critical slope

and the slope classification.