A smooth metal flume $($n$=0\mathrm{.}012)$ of semi$-$circular cross$-$section has a diameter of $1\mathrm{.}8$ m and a slope of $0\mathrm{.}005.$ What diameter of corrugated metal flume $($n$=0\mathrm{.}025)$ will be required for the same capacity? Answer: $2\mathrm{.}4$ m