CIV E 445 - APPLIED HYDROLOGY SPRING 2009 - MIDTERM 2 - SOLUTION

PROBLEM 3: ESSAY QUESTIONS

• 1 sq mi.

• The time of concentration is a function of L (length), n (roughness), S (slope), and i (rainfall intensity).

• m = 1.667 = 5/3.

• The four variables (or parameters) of the runoff curve number method are:
  
  
  1. Hydrologic soil group: A, B, C, D.

  2. Land use and treatment class: agricultural, urban, range, forest.

  3. Ground surface condition: poor, fair, good

  4. Antecedent Moisture Condition: I, II, III.

• The Horton abstraction model is (a) substractive, (b) cause-effect (more infiltration leads to less runoff), (c) bottomless (infinite soil depth).

  The Mockus (runoff curve number) abstraction model is: (a) additive, (b) cybernetic (biofeedbacks; more inflitation lead to more runoff), (c) has finite soil depth.

• The NRCS Type II storm, which covers the internal continental U.S., excluding the Eastern seaboard, the coast of the Gulf of Mexico, and the Pacific Coast.

  

  

• According to the Gumbel method, the return period of the mean annual flood is 2.33 years.

• Around the middle of the climatic spectrum, say 800 mm of mean annual precipitation. Example: the state of Idaho, where droughts have a tendency to last longer.

• The correlation coefficient for this case would be zero.

• Levees help protect rivers from overflowing their banks more frequently. However, disadvantages are:

  • they provide a false sense of security as floods increase in magnitude and frequency with upstream development,

  • when they fail, the results are usually catastrophic,

  • they starve the floodplain of nutrients, and

  • they produce the loss of "the sight of the river."

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