(a) Explain how it is possible for the flow at a particular cross-section in a channel to occur at two significantly different (alternate) depths of flow at the same discharge. (b) Water flows down a rectangular channel 4.0m wide at a depth of 1.7m. The discharge is 15.0m3 /s. (i) Determine whether the flow is subcritical or supercritical. (ii) Calculate the second (alternate) depth of flow that could occur in the channel at the same discharge. (iii) Determine the critical slope of the channel assuming that it is lined with concrete with a Manning n of 0.012s/m1/3.