Soil and Water Erosion

A parabolic grassed waterway is designed to carry a peak discharge $Q = 3.6\text{ m}^3\text{/s}$ at a maximum permissible velocity $v = 1.2\text{ m/s}$. The design central water depth is $y = 0.60\text{ m}$. For a parabolic cross-section where flow area is given by $A = \frac{2}{3} T y$ (with top width $T$), the required top width $T$ in metres is ________ (round off to 1 decimal place).