Problem: A culvert under a road must be $30$ m long, have a slope of $0\mathrm{.}003,$ and carry $4\mathrm{.}3m\frac{3}{s}$ of discharge. If the maximum permissible headwater level is $3\mathrm{.}6$ m above the culvert invert, what size of corrugated$-$pipe $(n=0\mathrm{.}025)$ would you select? Neglect approach velocity. Assume square$-$edged inlet with $Ke=0\mathrm{.}5$ and $Cd=0\mathrm{.}65.$ The outlet will discharge freely.