A brickwork rectangular channel is 120 {~cm} wide and laid on a slope of 2 {~m} per {km}. (a) Determine the normal flow rate when the water depth is 40 {~cm}. (b) For the same slope, find the water depth that will double the flow rate in part (a). Comment.
a. 0.22 m³/s, 80 cm
b. 0.20 m³/s, 70 cm
c. 0.25 m³/s, 90 cm
d. 0.18 m³/s, 60 cm