a river reach has flow of 350 ft3 /sec in trapezoidal channel with a bottom width of 14 ft and side slopes of 7:2 (h:v). the channel reach is 1300 ft long. channel bottom elevations at upstream and downstream of the reach are 146 ft and 141 ft, respectively. estimate the channel depth. the channel roughness is equivalent to earth, uniform section, graveled soil.