$,$ backwaien, $15\mathrm{.}7\mathrm{.}6m$

$9.$ The flow rate in a trapezoidal channel on a slope of $0\mathrm{.}0005$ is $14\frac{m^3}{s}.$ The bottom width of the channel is $3m,$ the side slopes are $1V$:$2H.$ Manning's roughness coefficient is $0\mathrm{.}025.$ At an embankment the flow is carried by a culvert; the water backs up in the channel. The headwater depth at the culvert is $4m.$ Determine the type of water surface profile upstream from the culvert. Using the direct step method, determine in two steps the distance from the culvert to the beginning of non$-$uniform flow in the channel. $,$ backwater, $($:$6761\mathrm{.}2(m)\}$