$(20$ points$)$ A sewer running $0\mathrm{.}7$ times full at maximum flow rate for a community provided with a separate system, serving a population of $80,000.$ What is velocity of sewer flow in this system? The water supply is $\backslash (190\backslash$mathrm$\{$~L$\}/\backslash )$ Capita$/$D $($Iped$),$ assumes a Manning coefficient roughness of $0\mathrm{.}013$ and permissible gradient of $1$ in $600.$

$(20$ points$)$