$8\mathrm{.}3\mathrm{.}1$ Determine the $4-$hr unit hydrograph using the following data for a watershed having a drainage area of $200k{m}^2,$ assuming a constant rainfall abstraction rate and a constant baseflow of $20\frac{m^3}{s}.$

$\backslash$table$[[$Four$-$hour period,$1,2,3,4,5,6,7,8,9,10,11],[$Rainfall $(cm),1\mathrm{.}0,2\mathrm{.}5,4\mathrm{.}0,2\mathrm{.}0,,,,,,,],[$Storm flow $(\frac{m^3}{s}),20,30,60,95,130,170,195,175,70,25,20]]$