A RESEARCH ON THE SOLUTE TRANSFER BY UNSATURATED FLOW IN POROUS MEDIUM

本研究旨在弄清非饱和土壤中溶质运移的特征，并对这一现象进行模拟。本研究涉及两个主题，即(1)平流-弥散过程的模拟和(2)土壤与土壤水之间的离子交换特性。为了研究第一个主题，我们进行了一系列饱和-非饱和条件下的混相置换实验，使用几种尺寸的玻璃微珠(平均直径)。：0.25 mm、0.5 mm、0.75 mm)作为多孔介质。非饱和条件下的实验表明，除饱和附近外，弥散系数随孔隙水平均流速的增大而增大。随着饱和度的增大，它开始减小。我们用湍流领域中常用的混合长度的概念来理解这种现象。为了应用这一概念，根据土壤水分特征曲线和非饱和导水率估计了孔隙水速度的变异性。TH…分析得到的混合长度，非饱和条件下为平均粒径的8倍，饱和条件下为1.8倍。为了对这些现象进行一般性的讨论，我们又做了一组实验，使用较大的直径(平均直径：3.7 mm，6.8 mm，9.1 mm)。与细小的玻璃微珠相比，混合长度相当大。它可以归结为在每个孔隙内发生的湍流混合。对横向的色散系数也进行了分析。混合长度是颗粒直径的1/10，这是不现实的。这方面的工作还有待进一步研究。土壤水中的离子交换采用野外测量和现场实验相结合的方法进行研究。试验山坡的地质为风化花岗岩。在4次暴雨中，每隔1小时对山坡上3个地点4个深度的雨水、溪水和土壤水进行采样。用离子色谱仪测定各样品的离子浓度。结果表明，在直接径流期间，Na~+呈下降趋势，而Ca~(2+)呈上升趋势。认为富Na~+基水是花岗岩层阳离子交换的结果，而在过程线顶端占主导地位的富Ca~(2+)水来源于表层。为了验证这一想法，用不同浓度的氯化钠和氯化钙溶液作为驱替水进行了现场实验。基于带离子交换项的ADE对模拟结果进行了数值模拟。在分析中，使用加彭公式作为质量作用量定律。数值模拟可以再现与实验结果相似的行为。较少

This research aims to make clear the characteristics of solute transfer in unsaturated soil and to model this phenomena. The resarch deals with two topics, i.e., (1) modelling of a advection-dispersion processes and (2) ion exchange characteristics between soil and soil water.To investigate the first topic, we conducted a series of miscible displacement experiments under saturated-unsaturated condition, using several sized of glass beads (average diameter. : 0.25mm, 0.5mm.0.75mm) as porous medium. It was revealed from the experiments in unsaturated condition that a dispersion coefficient increases with the average pore water velocity except in the vicinity of saturation. And it starts to decrease for the value of saturation. We comprehended this phenomena with concept of Mixing length usually used in the field of turbulence. To apply this concept, the variability of pore water velocity is estimated based on both soil water characteristic curve and unsaturated hydraulic conductivity. Th … More e mixing length obtained in the analysis is 8 times of averaga grain diameter for unsaturated condition and 1.8 times for saturated condition. To discuss the phenomena in general.we did another set of experiment using rather large size of diameter (average diameter : 3.7mm, 6.8mm, 9.1mm). The mixing lengths are rather large compared to fine glass beads. It may be reduced to the turbulence mixing occurring within each pore. The dispersion coefficient in transverse direction is also examined. The mixing lengths are 1/10 times of grain diameter which are unrealistic. We must wait for future work in this respect.The ion exchange in soil water are examined both by the field measurements and in situ experiments. The geology of the experimental hillslope is a weathered Granite. Rain water, stream water and soil water at 4 depths for 3 location on the hillslope are sampled each 1 hour during four storms. Ion concentration of each sample is measured by ionchromatograpy. From the results, Na^+ found to decrease in the period of direct runoff while Ca^<2+> tends to increase. This phenomena is considered that Na^+ rich base water is the result of cation exchange in Granite layr and Ca^<2+> rich water dominated at the peak of hydrograph is originated from surface layr. To make sure this idea, in situ experiments are conducted using different concentration of NaCl and CaCl_2 solutions as the displacing water. The results are numerically simulated based on ADE with ion exchange term. In the analysis Gapon's formula is used as law of mass action. The numerical simulation could reproduce similar behavior of the experimental result. Less