Calculation of Steady-State Evaporation for an Arbitrary Matric Potential at Ground Surface

Abstract

In the past few decades, many researchers have studied evaporation from soil columns in the presence of a water table. Several water retention functions have been developed to describe the water flow behavior in the field environment. While most studies involving these functions focus on analysis of water flow and solute transport in variably saturated porous media, there is a limited amount of research to estimate the evaporation rate at bare ground surface for an arbitrary matric potential head. In previous studies, Jury and Horton proposed a method of calculating the potential evaporation rate above a water table on the basis of the Haverkamp unsaturated hydraulic conductivity equation and an assumption that the potential evaporation rate is much less than the saturated hydraulic conductivity of the soil. In this thesis, I developed a new method to estimate the evaporation rate for an arbitrary matric potential head at bare soil surface. I also presented two programs to calculate evaporation rates for a wide range of depths and the fitting parameters of the Haverkamp equation. The results show that the evaporation rates calculated by this thesis fit well with the experimental data and can reproduce the result of potential evaporation rate calculated from previous equation under the special condition of an infinite matric potential head at bare soil surface.