Similarity on Water and Solute Movement in a Sand Column Induced by Evaporation.

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In order to clarify water and solute movement in a soil induced by evaporation in arid/semi-arid area, an evaporation experiment was undertaken by exposing the upper surface of a dune-sand column set initially at field capacity to atmosphere with constant temperature (25°C) and humidity (20%). The following results were obtained. (1) A time-variation in a vertical profile of water content in the sand column is described through Boltzmann transformation, i.e. using a function of X/√t (=λ), where X is depth and t time. (2) Vapor flux through the sand surface (evaporation rate) decreases in inverse proportion to √t and an evaporation location moves downwards in proportion to √t. (3) Local evaporation strength is given by a function of λ divided by t. (4) Vapor density ahead of drying front varies following a function of λ. (5) Solute such as Na+, Ca2+, Cl- and SO42- appears through dissolution of sand particles and its local dissolution rate is given by a function of λ divided by t. (6) Salinity accumulation occurs significantly ahead of the drying front and vertical concentration profiles for solute species decrease exponentially with λ.<BR> Even when heat of approximately 550 watt/m2 was simultaneously applied on the upper surface of sand column, characteristics of (2), (4) and (6) were almost satisfactory, though the salinization ahead of the drying front developed more remarkably.
水文・水資源学会の論文