Instructions: Closed book, closed notes. Use engineering paper. When you are finished, staple your work in sequence, and return this sheet with your work. Answer only 10 questions.

1. Explain the dichotomy in specifying the downstream boundary condition when modeling dynamic waves with the implicit method. How can the dilemma be resolved in practice?

2. Explain why the unsteady flow feature of HEC-RAS is not likely to be applicable to the determination of flood stages for typical hydraulic design.

3. Explain why the Vedernikov criterion is necessary but not sufficient to produce roll waves in steep channels.

4. The inherently stable channel has a value of rating exponent β = 1, which corresponds to a neutral-stability Froude number F_ns = ∞. Give that the maximum possible value of Froude number is not likely to exceed F_max = 25, what is the value of β corresponding to this maximum Froude number?

5. What two kinds of errors arise in numerical modeling? Explain which one is related to stability, and which one to convergence. Why is numerical modeling a compromise between stability and convergence?

6. Why is the backward-in-time/backward-in-space model of the kinematic wave equation likely to underestimate the peak flow?

7. What is topology in the context of computational hydrology?

8. What is the effect of the weighting factor θ in implicit numerical modeling using the Preissmann scheme?

9. A negative sand wave (due to sand mining in a river) may travel upstream or downstream? What type of analysis will show only downstream propagation? Explain.

10. Why is the failure of a nonengineered dam, resulting from a slide, likely to have a smaller peak outflow than that of a typical engineered dam?

11. Explain why an explicit scheme may be better than an implicit scheme in two-dimensional groundwater modeling.

12. What is the determining factor in the occurrence of circulation in a river embayment?