A Consideration on Numerical Model for the Relationship Between Evaporation Efficiency and Volumetric Water Content

It is important to obtain the amount of evaporation from the slope surface to analyze slope stability after rainfall. The bulk method is one of the evaporation estimation methods. Using this method, the amount of evaporated water from bare ground surfaces can be estimated from the general meteorological data. The evaporation efficiency, β, is an important parameter of the bulk method and is influenced by the volumetric water content in unsaturated soil. The molecular diffusion distance, F(Wv), is also an important parameter to calculate β. F(Wv) is influenced by the type of surface soil, the void ratio, and the volumetric water content, etc. The functional form of F(Wv) was obtained from experiments, and the experimental relationships between the volumetric water content and F(Wv) for loam and sand were explained by Kondo et al. In this paper, a numerical model for the molecular diffusion distance, F(Wv), derived from soil parameters such as grain size and void ratio is proposed, and β obtained from our proposed numerical model is compared with the results of laboratory tests by Sako et al. As a result, the applicable scope of the numerical model and the necessity of improvement of the numerical model are discussed.