Determining unsaturated hydraulic conductivity of dune sand at low pressure head from a steady-state evaporation experiment

摘要

Unsaturated hydraulic conductivity (K (#theta#) in the low pressure head range is important to predict evaporation rate accurately. The purpose of this study was to investigate the properties of a steady evaporation method described by Fujimaki et al. (1999) in application to sand. K (#theta#) of Tottori sand and Mu Us sand at low pressure head were determined in a steady evaporation experiment which used a soil column under constant meterorological condition having a constant pressure head at the bottom. Two procedures, “water content gradient method (WGM)” and “inverse method”, were used to estimate K(#theta#) in high pressure head range and has upper limit of water content for reliable estimation. On the other hand, inverse method gave physically odd estimates of K(#theta#) in the wet range when an empirical equation proposed by Fujimaki et al. (1999) was used for Tottori sand. An alternative empirical equation was proposed and was satisfactory. Effects of pressure head at the bottom, #psi#bot, on evaporation rate, pressure head near the soil surface and time required to reach steady state were investigated using numberical experiment. It was shown that the range of proper #psi#bot of sand was much narrower than that of sandy loam reported by Fujimaki et al. (1999). A procedure to determine proper #psi#bot using K(#psi#) obtained in high K range was suggested.