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Steady flow occurs through a trapezoidal channel with a bed width of 6.1 ft and side...

Steady flow occurs through a trapezoidal channel with a bed width of 6.1 ft and side slopes of 3:2. A 0.70-ft step occurs in the channel bed causing a head loss equal to 15% of the downstream velocity head. The flow depth upstream of the step is 4.3 ft and the cross-section-averaged velocity is 3.6 ft/s. What will be the change in the water surface elevation downstream of this step? How high would the step need to be to cause minimum specific energy downstream of the step?

Engineering   Civil-Engineering   
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Answer #1

In such questions we have to first determine the nature of flow ie whether it is critical, sub critical or super critical flow.This can be decided by obtaining the Frouds number of the flow. If Frouds no. is equal to to 1 then flow is critical, if less than 1 flow is sub critical, if greater than 1 flow is super critical. Now in case of sub critical flow water depth increases at downstream due to hump in the flow and in super critical flow waters level decreases at downstream due hump.

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