寒区土壤水冻融循环对入渗影响机理及模型研究

The freezing and thawing of soil change the conditions of infiltration and influence the hydrological processes such as runoff and infiltration and so on. Understanding the impact of permafrost on the infiltration from mechanism and characterizing the frozen soil infiltration using theoretical model are rarely reported. On the basis of soil freeze-thaw and infiltration experiments, we will illuminate the mechanism of various factors influencing on soil freezing and thawing, grasp the law of soil freezing and thawing cycles, reveal the effect of soil freeze-thaw on soil hydraulic properties, clarify the changes of hydraulic properties parameters, and then improve the Green-Ampt model which is a theoretical model based on physical mechanism to adapt the characteristics of the frozen soil. The performances of the improved model and the original model will be tested, and then continuously improve the applicability and reliability of the model. Finally, the improved infiltration model will be employed by a distributed hydrological model which is established to the characteristics of cold region, in which a typical area will be selected for the construction of the hydrological model. The effect of soil freezing and thawing on soil infiltration and hydrological cycle in cold region will be analyzed using the simulation results from the hydrological model. This research may contribute to the interaction between the frozen soil theory and the permafrost hydrology theory, and it is also a beneficial attempt of improving a theoretical infiltration model for cold region.

寒区冻土冻融循环改变了土壤的入渗条件，从而对寒区的产流、入渗等水文过程产生重要影响。从机理上认识冻土对入渗的影响以及刻画冻土入渗的理论模型尚不多见。本项目拟在开展土壤冻融和入渗实验的基础上，阐明各种影响因素对土壤冻融的作用机理，把握土壤冻融循环的规律，揭示土壤冻融对土壤水力学性质的影响，确定相关水力学性质参数的变异特征，在此基础上对Green-Ampt模型进行改进，建立具有寒区冻土特点的理论入渗模型。利用冻土入渗实验数据对模型改进前后的性能进行检验、对比，不断提高模型的适用性和可靠性。最后将改进的入渗模型嵌入针对寒区特点建立的分布式水文模型中，选取寒区典型区进行模型构建，再从模拟结果中分析土壤冻融引起的土壤入渗变化规律以及对寒区水文循环的影响。本研究有望对寒区冻土理论和水文学理论的交叉与发展做出贡献，也是对入渗理论模型在寒区改进的有益尝试。

寒区冻土冻融循环改变了土壤的入渗条件，从而对寒区的产流、入渗等水文过程产生重要影响。不加改进地直接采用现有土壤入渗模型进行寒区土壤水动态模拟，势必影响寒区水文过程模拟的精确性。为此，项目在系统总结已有研究成果的基础上，通过开展室内外冻土观测实验，研究了土壤水冻融机制和土壤水力学性质的变化，建立了适用于寒区冻土入渗过程的Green-Ampt模型，并在寒区典型区进行了成功应用。取得的重要结果：.（1）进一步明确了寒区土壤水的冻融机制。影响土壤冻融循环规律的任何因素都是通过改变两个基本条件来实现的：土壤温度和土壤含水量。不同土壤类型实质上也是由于土壤热量传递性质的差异和持水能力的不同具有不同的土壤温度和含水量，因此产生不同的冻融规律。.（2）测定了土壤冻结条件下的部分水力学性质。冻土入渗观测实验证明，尽管非饱和冻土层存在一定的渗透性，但是相对于未冻土而言，仍然可以在水文研究中作为隔水层对待。.（3）针对寒区冻土的冻融机制，对Green-Ampt模型的应用条件进行了改进。增加了一个土壤温度模拟方程，以提高模型在冻土入渗模拟中的适用性。当土层的温度低于设定的阈值时，该土层的水分冻结，在水文模型中作为不透水层处理。.（4）将改进后的Green-Ampt模型嵌入分布式水文模型MODCYCLE模型中，以三江平原为高纬度寒区季节冻土分布典型区，开展了水循环模拟与水资源调控应用。.（5）截止目前，本项目发表学术论文5篇，其中SCI/EI检索期刊4篇，申请发明专利6项，获得软件著作权2项，培养青年骨干1 名、硕士研究生2名。.项目针对冻土的Green-Ampt模型改进是对土壤入渗模型的有益补充，进一步增强了该模型的普遍适用性。同时，考虑冻土改进后的分布式水文模型具有了更加广泛的应用前景，可以适应我国各种气候条件下的水文模拟。