a nearly horizontal, 12 ft wide rectangular channel carries 60 cfs at a depth of 3 ft. the width of the channel is smoothly contracted to 6 ft at the downstream section. (a) determine if the flow will choke and both the downstream and upstream water depths. (b) if there is also a 1 ft high step up in bottom elevation at the contraction, determine if the flow will choke and both the downstream and upstream water depths