$29$ A trapezoidal concrete channel has a constant bed slope of $0\mathrm{.}0015,$ a bed width of $3\mathrm{.}0m,$ and side slopes of $1$:$1.$ It carries a discharge of $20\frac{m^3}{s}.$ The channel is a tributary to a river in which the existing flood level is $3\mathrm{.}5m$ above the channel bottom. Compute the water surface profile by the numerical integration method to a depth $5\%$ greater than the uniform flow depth. $=1\mathrm{.}1$ and $n=0\mathrm{.}025.$