CIV E 530- OPEN CHANNEL HYDRAULICS
FALL 2005
FIRST MIDTERM
OCTOBER 10, 2005, 1600-1715

Name: _________________________ Red ID ________________________ Grade: _______

Instructions: Closed book, closed notes. Use engineering paper. When you are finished, staple your work in sequence (1 to 3), and return this sheet with your work.


  1. (20%) A natural canyon (hydraulically wide) is subjected to an extreme flood event, which approximates the Probable Maximum Flood. You are asked to provide a quick estimate of the flow depth. Since supercritical flow is rare in nature, critical flow may be assumed as a first approximation. What is your best estimate of the flow depth?

  2. (20%) A rectangular overflow spillway is 20 ft wide, and the design head is 0.8 ft. What is your best estimate of the discharge?

  3. (60%) Please answer the following questions in a brief statement.

    1. What is the relative Lagrange celerity? What is its importance in open-channel flow?

    2. What is the practical range of β (exponent of the discharge-stage rating)? What is the value of β for a hydraulically wide channel with Chezy friction?

    3. What is potamology? Why is it important in open-channel hydraulics?

    4. Why is the total discharge Q hydrologic, while the unit-width discharge q is hydraulic? Explain with examples.

    5. In what case is the value of α (velocity distribution coefficient) equal to 1?

    6. In what case does the gradually varied flow assumption fail to apply? Be specific; name an example.

    7. Does HEC-RAS account for movable-bed (alluvial) rivers? Does it account for unsteady flow?

    8. Using the dimensionless Chezy formula, estimate the maximum Froude number that can be achieved in practice. Can a value F = 50 exist in the real world? Why? (Or, Why not?)

    9. What four forces are usually considered in open-channel flow calculations? Why are wind forces not included on this list?

    10. What is a control in open-channel hydraulics? State the two major types of controls in open channels.

    11. What equation (or concept) was missing from Chezy's original analysis?

    12. Can unsteady uniform flow exist? Why? Or, Why not? Did Chow made a mistake when naming Section 8.8 of his book "Instability of uniform flow". Why? (Or, Why not?)