Page $5$

$4.(12$ pts$.)$ The site illustrated in Figure covers $25$ ha$,$ of which the meadow $($good condition$)$ of soil group D covers $7\mathrm{.}5$ ha$,$ residential $(\frac{1}{2}$ acre lots$)$ of soil group C covers $6\mathrm{.}3$ ha$,$ the rest is open spaces$/$lawns $($good condition$)$ of soil group D and it covers $11\mathrm{.}2$ ha$.$ The site is graded such that all of the runoff is routed to a retention area. For a storm with a precipitation of $7\mathrm{.}87$ in $,$ calculate the volume surface runoff $(m^3)$ that enters the retention area.