Given:

An undeveloped $1000$ acre catchment currently is covered by pasture in good condition and is composed of

hydrologic soil group C$.$ This gives a pre$-$development composite SCS CN equal to $74.$

A proposed urban development $($post development$)$ will change the land use to:

$55\%\frac{1}{3}$ acre lots $(30\%$ impervious$),CN=81$;

$20\%$ in open space in good condition, $CN=74$;

$25\%$ in roads, sewers and parking lots, $CN=98.$

answer the following questions:

The post$-$development composite SCS CN is:

a$)90\mathrm{.}2$

b$)78\mathrm{.}6$

c$)83\mathrm{.}9$

d$)89\mathrm{.}5$

The pre$-$development direct runoff $Q$ associated with a $10-$yr$,24-$hr rainfall of $P=3\mathrm{.}2$ inches is

$($Note: $CN=74)$:

a$)2\mathrm{.}5$

b$)1\mathrm{.}5$

c$)1\mathrm{.}0$

d$)2\mathrm{.}1$

The post$-$development direct runoff $Q$ associated with a $10-$yr$,24-$hr rainfall of $P=3\mathrm{.}2$ inches is:

a$)3\mathrm{.}2$

b$)2\mathrm{.}8$

c$)1\mathrm{.}3$

d$)1\mathrm{.}7$