山坡尺度降雨产流过程中的“旧水”悖论研究

Runoff generation processes is a basic research content of hydrological science. Recently, many studies found that slope runoff was constituted by a large amount of pre-event water (i.e., old water) based on tracing experiment conducted in the hillslope scale. This finding is contrary to the traditional theories of runoff generation which says that runoff water is mainly constituted by event water (i.e., new water). The phenomenon is called “old water” paradox. However, the physical mechanisms of “old water” paradox are still can’t be understand very well, and most studies are mainly focused on the conceptual interpretations. In addition, the understanding on the specific feature of “old water” paradox in subhumid regions is still limited. Therefore, we plan to research on the “old water” paradox in a hillslope scale. The headwater catchment of Miyun Reservoir in China is selected as the study area considering that several previous studies have been conducted in the area by the applicants. We plan to do high frequency hydrometric and hydrochemical observation in site for analyzing the characteristics of rainfall-runoff processes on a hillslope. We also plan to construct a two-dimension hillslope runoff model which couples both water flow and solute transportation processes. The transient time of rainfall in the hillslope will be calculated, and the rainfall water flow path will also be analyzed through using numerical simulation. The hillslope runoff generation processes in regions with different geological and topographic features under different climate and hydrology conditions will plan to be simulated through setting thousands of simulation scenarios. The goals of this projects are: to analysis the specific patter of “old water” paradox in subhumid area, and to reveal the physical mechanism of “old water” paradox. Expected results will be helpful to enrich the current theories of runoff generation，to improve the understanding of the contaminant transport processes, and to enhance the physical mechanism of hydrological model and contaminant transport model.

产流是水文科学研究的基本内容。传统的产流理论认为产流水主要由本场次降水（新水）组成，而基于示踪过程的山坡观测实验发现产流组分中含有大量的前事件水（旧水），这一现象与传统的产流理论相悖，即“旧水”悖论。现有的研究对“旧水”悖论物理机制的揭示还比较初步，对半干旱半湿润区“旧水”悖论表现形式的理解还不够深入。本申请项目拟在申请者已开展工作的基础上，以密云水库源头区实验山坡为例，通过高频次的水文、水化学和同位素观测，分析山坡降雨产流特征。通过构建耦合水动力学和溶质运移过程的二维山坡产流模型，解析雨水在山坡的滞留时间和具体流动路径，模拟不同地质地貌下垫面地区在不同气象水文条件下的山坡产流过程，揭示半干旱半湿润区“旧水”悖论的具体表现形式及物理机制。预期成果将有助于发展现有的产流理论，促进对污染物运移机理的理解，进一步完善现有水文模型和污染物运移模型的物理机制。

产流是流域水文过程的重要组成部分。对产流过程中的“旧水”悖论研究有助于深入理解流域水文过程和污染物运移过程，可为山洪预报和流域精细化管理提供理论支撑。项目以位于华北土石山区的北京西台子小流域为实验观测流域，基于野外观测数据，分析了西台子实验流域的降雨产流特征，揭示了“旧水”在研究区的主要表现特征，分析了降雨产流过程的主要影响因素。项目分析了土壤水对径流过程的影响，发现研究区土壤水中存在“两个水世界”假说；探讨了山杨树根-土界面水力再分配现象对土壤水分的调节作用，为区域水土保持和水生态环境保护提供理论支撑。项目合作构建了三维山坡水文水动力和溶质运移模型，实现了对山坡水流和稳定同位素运移过程的耦合模拟，为山坡水文和污染物运移过程研究提供了方法支撑。此外，项目还分析了影响径流过程的主要影响因素，量化了我国不同土地覆盖/利用类型下的土壤稳定入渗率和饱和导水率，阐释了饱和导水率的主要影响因子，为土壤入渗过程研究提供了理论和数据基础。项目量化了我国小流域基流退水参数的取值范围，分析了影响退水参数的主要因子，获得了退水参数的通用方程，并对退水参数通用方程进行了验证和移植，为中小河流精细化管理和无资料区径流过程模拟提供了数据支撑。