QUESTION $\backslash (3[20\backslash )$ Marks$]$

Fig Q$3$ presents a section of an asphalt$-$surfaced road. The road carries a $100-$year flood flow of $\backslash (2\mathrm{.}3\backslash$mathrm$\{$~m$\}^\{3\}/\backslash$mathrm$\{$s$\}\mathrm{.}15\backslash$mathrm$\{$~cm$\}\backslash )$ curbs bound the road bed. The longitudinal slope of the road is $\backslash (3\backslash \%\backslash ).$

$3\mathrm{.}1.$ Determine if all the flow is carried within the roadbed $($between the curbs$).$ Support your answer with detailed calculations. Assume that asphalt has a Manning's roughness coefficient $\text{'}\backslash ($ n $\backslash )\text{'}$ of $0\mathrm{.}015$

$[20$ marks$]$