土壤非均匀水流运动与溶质运移的两区-两阶段模型

Modeling the heterogeneous soil water flow and solute transport by two-region-two-stage model

根据优先流发展过程中所表现出来的阶段性特征和分形特征,建立了描述非均匀土壤水流运动和溶质运移过程的两区-两阶段模型。模型认为,研究区域可划分为水流经过的活动流场(即优先流流场)和水流绕过的不活动流场两个区域;优先流流场在发展过程中将先后经历流场扩张和保持两个阶段;处于扩张阶段的优先流流场,其内部土壤水流运动的快速非平衡特征明显,并表现出明显的分形特征;处于保持阶段的优先流流场,其内部的土壤水流运动类似于基质流运动,无明显的分形特征。通过在砂土、壤土和黏土条件下开展的6个示踪试验,检验和评价两区-两阶段模型、活动流场模型和两区模型模拟预测非均匀土壤水流运动和溶质运移的有效性。研究结果表明,两区-两阶段模型可较好地描述各种土质条件下的优先流运动;活动流场模型对壤土和黏土条件下的优先流运动预测精度较好,而对砂土条件下的优先流预测精度较差;两区模型对各种土质条件下的优先流运动预测精度均较差。

According to the stage and fractal characteristics those preferential flow presents, a two-re- gion-two-stage model （TTM） is developed in this paper. The TTM divides the whole flow region into the mobile （i.e. preferential flow） and immobile （i.e. bypass） regions. As flow continuing, the preferential flow region expands firstly to the maximum value and then keeps unchanged. When the preferential flow region expands, the infiltrated water moves rapidly with high non-equilibrium, and presents obvious fractal charac- teristics. After the preferential flow region expanding to the maximum value, it keeps unchanged and the in- filtrated water moves slowly, similar to the matrix flow, and presents no fractal characteristics. Six tracer in- filtration experiments were conducted in sand, loam and clay to compare efficiency of TTM, active region model （ARM）, and mobile-immobile region model （M1M） in representing the preferential soil water flow and solute transport in those three soils. Modelling efficiency comparison indicated that, the TTM captured the preferential flow behavior in all the three soils; while the ARM generated good predictions for the flow and transport in loam and clay only, the preferential flow behavior in sand was badly captured by the ARM. On the contrary, MIM failed to capture the preferential flow behavior in all the three soils.