考虑微地形的坡面水文非线性化耦合机理研究

Take mountainous hydrologic processes as the research obeject, this research focuses on the nonlinear hydrologic processes based on the comprehensive function of topography of grid cells and micro-topography of sub-grid cells in distributed hydrologic model. Using the method of hydrology, hydraulics, environmental dynamics, hydrologic tracer technique, this study emphasises on local microtopography affects soil water redistribution and overland flow path recombination, whose changes lead the characteristic varieties of nonlinear hydrologic processes on hillslope cells, and their feedbacks in the distributed hydrologic modeling. Multi-scale experiments in lab and field and theoretical coupling numeric analysis are designed to quantify the effective porosities in heterogenious soil structures and soil physical properties, the function of infiltration on heterogeneous hillslope is defined. Then change the various saturations of soil water content in soil vadose zone, the occurrence and intensities of preferential flows are measured, and the contributions of preferential flows and matric flows in various saturation are evaluated for runoff generation in heterogeneous hillslope. Based on the statistic characteristics of micro-topography, find the relationships between spatial redistribution of infiltration, preferential converge path on hillslope surface and micro-topography, disclose the mechanism of micro-topography affecting the redistribution of surface water ponding and nonuniform infiltrations. Additionally, with the various scaling experiments, full coupling distributed hydrologic model is utilized for numeric tests with heterogeneous properties in subcells, the spatial scale effects are disclosed based on tests. The study will attempt to solve the consistency issues between high-resolution terrain data with small-scale hydrological pattern and watershed hydrologic modeling by large grid cells, the result could support the trans-scale application and nonlinear coupling for multi-processes distributed hydrologic model.

以坡面水文过程为研究对象，运用多尺度的室内、外水文实验和数值耦合理论，研究分布式水文模型中网格地形与次网格微地形综合作用下的水文过程非线性化问题。本研究将运用水文学、水力学、环境动力学、水文示踪技术研究坡面微地形对局地土壤水分布改变引起的产流模式改变、对局地汇流路径改变引起的坡面汇流特征变化，以及这些非线性问题在分布式模型计算中的反馈。运用水文示踪法确定土壤非均质结构特征及物理属性,分析优先流触发的条件、发生强度与土壤水饱和度关系，揭示包气带优先流与基质流并存时径流分割的非线性关系；确定微地形参数与非均质渗流（产流）和优先汇流的内在关系，揭示微地形引起下渗量再分布与地表径流再分布的量化特征,并借助理论模型分析次网格非均质属性的尺度效应。本研究将尝试解决高分辨率地形数据和小尺度水文机理模式与流域大网格水文计算的一致性问题，为多过程分布式水文模型的非线性耦合和跨尺度应用提供支持。

本研究以微地形坡面水文产汇流机制为研究对象，选择典型的小流域进行多尺度的室内外实验，研究网格化坡度及次网格微地形综合影响下的产汇流非线性化问题。针对非饱和混合产流引起的非线性问题，先通过理论推导和模拟计算不同土壤类型、在不同饱和度和雨强条件下非饱和产流过程，再借助数值优化原理提取Horton和格林安普特的变元参数规律，反推出非饱和产流的非线性化规律；改进考虑坡度的二维产汇流方程组，结合点参数升尺度方法，修正网格化计算的坡度效应；在此基础上，利用坡面微地形对比分析，采用糙度指数定量化计算了各实验区微地形对产流和土壤水再分布的影响规律，分析得出了微地形影响深度和洼地积水分布频率与产汇流特征值的相关性，提出了概化微地形影响的参数修正和率定方法；在实验流域构建了考虑微地形影响的三维地表-地下水耦合模型系统，结果表明模型系统能充分考虑局地地形和非饱和含水率对产流过程影响，变化饱和带和微地形指数、地表地下水耦合系数能定量化复杂山坡流域的产流非线性化过程；长序列历史洪水模拟计算表明微地形对降水初期影响显著，并随着降雨持续而逐渐减弱，微地形引起的饱和带扩张产生直接径流是形成洪峰流量的主要贡献。本研究解决高分辨率地形信息与网格化计算尺度、计算效率之间的一致性问题，通过修正参数的时变规律实现小尺度水文产流机理与计算空间尺度相匹配，为多过程耦合的分布式水文模型参数优选提供参考。