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

本研究旨在明确非饱和土壤中溶质迁移的特征，并建立该现象的模型。研究涉及两个主题，即(1)平流-扩散过程的建模和(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，我们在饱和-非饱和条件下进行了一系列的混相驱替实验，使用了几种尺寸的玻璃微珠（平均直径）。多孔介质：0.25mm、0.5mm、0.75mm)。非饱和条件下的实验表明，除饱和附近外，分散系数随孔隙水平均流速的增大而增大。饱和度的值开始减小。我们用湍流领域中常用的混合长度概念来理解这一现象。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孔隙水速度的变异性。分析得到的混合长度为非饱和条件下平均粒径的8倍，饱和条件下平均粒径的1.8倍。讨论一般的现象。我们又做了一组比较大直径的实验（平均直径3.7mm, 6.8mm, 9.1mm）。与细玻璃微珠相比，混合长度相当大。它可以简化为发生在每个孔内的湍流混合。并对横向色散系数进行了分析。混合长度为颗粒直径的1/10，这是不现实的。我们必须等待这方面今后的工作。通过田间测量和现场试验对土壤水分离子交换进行了研究。实验山坡的地质是风化的花岗岩。在4次暴雨期间，每1小时在山坡3个地点的4个深度取样雨水、溪水和土壤水。用离子色谱法测定每个样品的离子浓度。结果表明，Na^+在直接径流期呈下降趋势，而Ca^<2+>呈上升趋势。这一现象认为，富Na^+碱性水是花岗岩层内阳离子交换的结果，而以线峰为主的富Ca^<2+>碱性水来源于表层。为了验证这一想法，用不同浓度的NaCl和CaCl_2溶液作为置换水进行了原位实验。基于离子交换项的ADE对结果进行了数值模拟。在分析中，采用Gapon公式作为质量作用定律。数值模拟可以再现与实验结果相似的行为。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