A trapezoidal canal with a bottom width of 2 m, a side slope Z=1.5, and a longitudinal slope of 0.0006 conveys a flow rate of 3 m^3/s. If the water depth in section 1 is 0.78 m and in section 2, 190 m downstream of section 1, the water depth is 0.63 m, compute the coefficient of roughness.