湿润山丘区小流域关键带结构与水文连通性研究

Upstream areas are where the flood events are generated in humid region. Upstream hillslopes, valleys and ephemeral channels provide quick pathway for flood events and in most time they flow seasonally or only after rain, i.e., the hydrological connectivity is ephemeral. Thus the dynamics of drainage network expansion and contraction, and connection and disconnection, may offer important clues to understanding the patterns and processes of runoff generation. However, the mechanism of what controls on hydrological connectivity and how it connects the hillslope, valley and channels is still far from being understood. Extensive field studies in diverse catchments around the world continue to characterize and catalogue the enormous heterogeneity of hillslope structures and complexity of rainfall runoff processes in more and more watersheds, and at different scales. But, these field findings seem to be meaningless for the modeler, as they have not usually incorporated the experimentalist’s knowledge into their models. Predictions across the whole catchment are extending beyond our fundamental understanding of hillslope hydrological processes. There are still so many fundamentals that we do not understand with regard to how catchment are composed, organized and connected through hillslopes, valleys and channels, and how catchment storage affects rainfall-runoff responses. In this study, Hemuqiao Catchment is selected as the experimental station and detail investigation of topological structures of hillslopes, valleys and ephemeral channels will be carried out. Through setting up a nested observation in the catchment, we try to reveal rainfall-runoff responses and hydrological connectivity affected by hillslope soil depth, bedrock terrain and drainage network structures, and to find a macroscale pathway hidden in the critical zone that is the pivot of the runoff and shapes its flow hydrodynamics in the whole catchment. Our studies about hydrological connectivity of hillslopes, valleys and ephemeral channels can help people understand the mechanism of runoff generation, and can narrow the gap between experimentalist and modeler, thus further develop hydrological theory and method.

山丘区是洪水的“策源地”，山坡、沟谷及间歇性河道为洪水的形成提供了通道，同时也是水文连通时空变化最为强烈的地带。然而，我们对流域表层关键带结构特征（如山坡土壤厚度、基岩地形、沟谷河道形态及组织规律）及其水文连通机制等的认识尚存不足。这限制了水文学理论及模型方法的发展和应用，如变化环境背景下或无（缺）资料地区的预测问题等。本研究选取和睦桥小流域为对象，通过勘测山坡、沟谷及间歇性河道的结构特征，揭示水流在山坡及沟谷地表、地下的宏观表象通道及其分布特征；通过建立小流域嵌套式的水文强化观测网络，研究这种宏观表象的快速通道的水流传输能力，揭示径流连通的动力学机制。山坡、沟谷及间歇性河道水文连通性实验的开展将进一步增进人们对产流规律的认识，有助于拉近野外实验与水文模型之间的距离，发展水文基础理论和方法。

本项目选取太湖源头区睦桥流域为研究对象，项目进一步强化了已有的观测项目，增设了河流水位、雨量、气象观测站和山坡径流场，围绕原位观测开展了大量的野外勘探和室内分析工作。研究揭示了山坡结构（地形、土壤）对水文连通机制的影响，研究发现90%事件的水文连通性是从土壤-基岩界面处缓慢建立，少数事件也可以通过上层滞水的方式快速建立；发现在山坡土壤由湿变干的过程中，土壤水分依旧可以通过非饱和侧向流的形式从边坡运动至谷地，并在谷地风化基岩与土壤的界面处产生“阻尼振荡”式下降规律，证明山坡由湿润到干旱的转化过程中地形也可以成为山坡土壤水分运动的关键控制因素。山坡关键带结构的分布与连通显著影响水文连通性和径流的产生。本研究推导了考虑地形影响的模拟土壤厚度演化的非稳态解析公式，给出了依据局部采样推求模型参数的理论方法，提出了土壤生成速率等参数估算的数学物理途径，发展了用于土壤厚度模拟及地形特征提取的数字流域模型技术，实现了对山坡地表地下结构分布和连通的高精度模拟计算。随后，本研究通过对关键带结构的合理概化，搭建了模拟原型实验的物理模型，并对单位宽度山坡含水层运动波动方程做了数理解析，推导了考虑山坡关键带结构要素的径流响应特征函数，实现了水文理论上的突破。目前，该项研究成果在太湖流域山丘区以及藏东南小流域工程水文计算中均得到推广应用。项目研究成果在水文水资源领域国内外顶级刊物如Water Resources Research、Journal of Hydrology、水科学进展等撰写论文16篇，其中SCI检索论文10篇，Ei论文1篇，申报了发明专利13项，软件著作权2项。项目培养硕博士研究生8名，出站博士后1名。