Enhanced Water Vapor Flow In Soils for Effective Use of Saline Groundwater for Desert Greening Technology.

We investigated the effect of enhanced water vapor flow in unsaturated soils to use saline groundwater in arid or semi-arid regions for irrigation purposes. A layer with relatively large particles, such as gravels, is known to intercept capillary rise of groundwater and/or to prohibit downward infiltration. These phenomena are known as capillary barrier. The basic idea of this study is to use intercepted liquid water during capillary rise at the gravel layer by transforming it to water vapor and transporting water vapor by an artificially created temperature gradient to the surface soil. This approach allows us to avoid surface soils from salinization. In this study we conducted column experiments and numerical simulations using HYDRUS to optimize parameters that control vapor transport in soils, including temperature gradients (or temperature), vapor diffusivitiy, soil hydraulic and thermal properties, and the thickness and position of the gravel layer. This study demonstrates that usually abundant heat energy in arid and semi-arid regions can be used to vaporize saline water and to transport water vapor toward desired locations.