CIV E 445 - APPLIED HYDROLOGY SPRING 2005 - MIDTERM 2 - SOLUTION

PROBLEM 3: ESSAY QUESTIONS

• An evapotranspirometer measures potential evapotranspiration; a lysimeter measures actual evapotranspiration.

• A catchment is small in a hydrologic sense if:
  
  
  1. rainfall can be assumed to be uniformyl distributed in time

  2. rainfall can be assumed to be uniformyl distributed in space

  3. storm duration usually exceeds time of concentration

  4. runoff is primarily by overland flow

  5. channel storage processes are negligible.

• The bed slope. The rule-of-thumb for kinematic flow is bed slope greater 1 percent (0.01).

• 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 standard value of peak-rate factor (PRF) of the NRCS synthetic unit hydrograph is 484. It comes from 2 × (3/8) × 645, in which 645 = 640 × 1.008, the latter being a conversion factor.

• The SCS Type II storm, which covers the midcontinental U.S., with the exception of California, the Pacific Northwest states (Washington and Oregon), the Eastern seaboard, and the Gulf Coast.

• The SCS TR-55 method is consistent with diffusion wave theory because it has built within it the capability to describe runoff diffusion (in the graphs for unit peak discharge, or peak discharge per unit of catchment area per unit of runoff depth).

• According to the Gumbel method, the return period of the mean annual flood is 2.33 years. This is because for K = 0 and n = ∞, the mean of the Gumbel variate is the Euler constant (0.5572).