A $2-$m$-$internal$-$diameter circular steel storm drain $(n=0\mathrm{.}012)$ is to discharge

water uniformly at a rate of $12\frac{m^3}{s}$ to a distance of $1\mathrm{.}3km.$ If the maximum

depth is to be $1\mathrm{.}5m,$ determine the required elevation drop.

The required elevation drop is

$m.$