Dr. Victor M. Ponce - Surface-water Hydrology, Homework Set #1

CIV E 634 - SURFACE WATER HYDROLOGY
SPRING 2003
HOMEWORK 2: EVAPORATION

From Eq. 2-37, the saturation vapor pressure gradient is: Δ = 1.447 mb (^oC^-1).
The net radiation in evaporation rate units is E_n = 585/(0.99821 x 586) = 1.00 cm/d.
From Eq. 2-59, the aerodynamic resistance is: r_a^rc = (208 X 86400)/(175 X 1000) = 102.7 s m^-1 = 1.027 s cm^-1.
The stomatal resistance of the reference crop is: r_s^rc = 200/L = 200/(24 x 0.12) = 69.4 s m^-1 = 0.694 s cm^-1.
From Table 2-4 and Eq. 2-51, the modified psychrometric constant is: γ* = (1.447/2.19) [1 + (0.694/1.027)] = 1.107.
The vapor pressure deficit is: (e_s - e_a) ≅ (e_o - e_a) = e_o[1 - (RH/100)] = 23.37 [1 - (85/100)] = 3.51 mb.
From Eq. 2-56, K = 7.51 X 10^-7 mb^-1, and thus, K' = 0.0649 mb^-1 s d^-1.
From Eq. 2-57, the mass-transfer evaporation rate is: E_a = 0.132 cm d^-1.
From Eq. 2-54, the evaporation rate is: E = 0.624 cm d^-1.