优先流研究现状及发展趋势

The present and future research on preferential flow

优先流是一种常见的土壤水分运动形式,它是土壤水运动机理研究由均质走向非均质领域的标志,但最初却没有真正的定义。综合介绍了目前国际上公认的土壤优先流定义、优先流多种表现形式及其重要特征,系统阐述了优先流的静态(内在)和动态(外在)影响因素、开展研究的基础理论以及实验研究技术,指出开展优先流研究可以有效及充分地解释早期水文学研究所困扰的不符合达西定律及对流-弥散方程等重大问题,但由于优先流运动过程具有非平衡性及区域特点,其自身类型较多,开展优先流研究同时加大了水文过程研究的难度及深度,所以长期以来没有得到充分重视,到目前为止,对于优先流运动机理尚未明确;开展优先流研究判定标准多样,但缺乏系统成形的判定标准;由于土壤本身就是异质性系统,对优先流研究需综合考虑尺度效应;虽然已有多种方法可以有效开展优先流研究,但缺少已获得国际标准认证的适用于具有快速环绕特性的优先流研究需要的现代仪器设备。同时还探讨了优先流研究的发展趋势。

Preferential flow, an ordinary form of soil water movement, was proposed recently but had not been properly defined at first even though this expression has been adopted by various scientific communities. Preferential flow is a term describing a process whereby most of the water and contaminants move through porous medium following favored pathways from other parts of the medium. Research on preferential flow involves studying the mechanism of soil water movement from homogeneous to heterogeneous fields, and it is inevitable that performing experimental or technological analyses is difficult because this movement is not detected easily. This paper provides a broad overview of preferential flow with respect to definitions, types, basic meanings, basic theory, important characteristics and effectual factors, and systematically outlines the most recent methods to study preferential flow with quantificational experiments such as chemical tracing, mini-tensiometry and electrical resistance tomography, as well as other methods. We also provide a detailed analysis of modern apparatuses used effectively in the above-mentioned technological methods such as time-domain reflectrometry （TDR）, tension infiltrometry and ground penetrating radar. Research that takes into account preferential flow can effectively explain the problems of hydrological processes which may not be addressed by Darcy＇ s law and the Convective-Diffusive Equation, but at the same time, considering preferential flow increases the difficulties and complexity of the research due to the non-equilibrium and regional characteristics and manifold types that are involved. To date, the mechanismof the movement of preferential flow still does not have a proper definition. There is a lack of systematic standards, which should take into account the spatial and temporal scale. There is also a lack of equipment that can obtain international standard authentication and that has high speed and bypassing characteristics necessary to measure preferential flow. In the end, the paper discusses the direction of the development of future research.