A rectangular channel is $3$ m wide and laid on a slope of $(0\mathrm{.}001)$ carries a flow of normal depth of $1\mathrm{.}2$ m sharp crested rectangular weir $($cd$=0\mathrm{.}02)$ is located with its crests at a $2$ m above the channel bottom at the downstream end of channel n$=0\mathrm{.}023$ compute the length of water surface profile and the name of it by using direct step method between A and B use three steps