A triangular shaped grassed waterway with a longitudinal slope of $2.5 \%$ is to carry a discharge of $1.5 \mathrm{~m}^{3} \mathrm{~s}^{-1}$ with a permissible velocity of $1.2 \mathrm{~m} \mathrm{~s}^{-1} .$ The side slope of the channel is 1.5: 1 (Horizontal:Vertical). Without considering free board, the top width of the channel in $\mathrm{m}$ is______________
A triangular shaped grassed waterway with a longitudinal slope of $2.5 \%$ is to carry a discharge of $1.5 \mathrm{~m}^{3} \mathrm{~s}^{-1}$ with a permissible velocity of $1.2 \mathrm{~m} \mathrm{~s}^{-1} .$ The side slope of the channel is 1.5: 1 (Horizontal:Vertical). Without considering free board, the top width of the channel in $\mathrm{m}$ is______________