CIV E 445 - APPLIED HYDROLOGY
SPRING 2014
LAB No. 2 SOLUTION

  1. The derivation is shown here.

  2. The saturation vapor pressure at T = 20°C is 23.37 millibars.

    The mass-transfer evaporation rate is:

    Ea = (0.013 + 0.00016 × 180) 23.37 × (70/100) = 0.6838 cm/d.

    The density of water at 20°C is 0.998 gr/cm3.

    The heat of vaporization at 20°C is 586 cal/gr.

    The net radiation is evaporation rate units is: Ea = 525/ (0.998 × 586) = 0.8977 cm/d.

    Penman's ratio at 20°C is α = 2.19.

    The evaporation rate is: E = (2.19 × 0.8977 + 0.6838) / (1 + 2.19) = 0.8306 cm/d.

    For the month of July: 0.8306 × 31 days = 25.75 cm.

    The results are confirmed by running online_penman.

  3. The annual temperature efficiency index is: J = 67.39.

    The c exponent is: c = 1.5564.

    The uncorrected PET is: PET = 9.38 cm.

    The PET correction for 40° N latitude for July is: K = 1.23.

    The corrected PET is: PET = 1.23 × 9.38 = 11.54 cm.

    The results are confirmed by running online_thornthwaite.