$($ii$)$ A unit hydrograph $(10$ mm$,2-$hour$)$ for a catchment is shown below.

$\backslash$table$[[$time $(h),0,1,2,3,4,5],[UH(\frac{m^3}{s}\frac{?}{cm}),0,2,12,15,8,3]]$

Using this unit hydrograph, predict the timing and magnitude of the peak flow at the downstream end of the catchment for an idealised twohour storm that has an intensity of $12mm$ per hour, followed by a twohour storm that has intensity of $7mm$ per hour. Assume a base flow of $2\mathrm{.}0\frac{m^3}{s}$

$[8$ marks$]$

$($iii$)$ Convert the hydrograph in $($ii$)$ into a $10mm,4-$hour unit hydrograph