A trapezoidal channel with a bed width of $5\mathrm{.}0$ m and side slopes of $1\mathrm{.}5H$: I V is laid on a slope of $0\mathrm{.}0004.$ Find the normal depth corresponding to discharges of $($i$)10\mathrm{.}0\frac{m^3}{s},$ and $($ii$)20\mathrm{.}0\frac{m^3}{s}$ in this channel. Use Table $3A.$I and take $n=0\mathrm{.}015$ for both cases.