多闸坝河网多源水龄时空分异特征及其水质效应

In order to break the limitation caused by a single exchange rate which is usually adopted to reflect the water exchange capacity of whole river, the following questions will be answered in this project: spatio-temporal variation characteristics of water exchange capacity in impounded river networks, its multi-source driving mechanism, and its quantitative water environmental effect. The water age is introduced to characterize spatio-temporal variation of water exchange capacity in river, and 4 tasks will be carried out: firstly, 1D&2D water age and water quality numerical model for large impounded river networks will be developed. Secondly, based upon long series of hydrological and water quality data, the spatio-temporal variation of water age and water quality will be simulated and the influence of dams will be analyzed to quantify the variation of water age in impounded river networks with higher spatial and temporal resolution. Thirdly, through numerical source analysis, the impact of different water sources and dams regulation on water exchange capacity will be quantified to reveal its multi-source driving mechanism. Lastly, through data mining, the quantitative response relationship between spatio-temporal variation of water quality and water age and its components will be inferred to reveal the impact of water exchange capacity on convection and change of water pollutants. Based upon the research results, water exchange capacity of river-networks will be quantified with higher spatial and temporal resolution to break the limitation caused by a single exchange rate; moreover, the water environmental effects of hydrology and hydrodynamics variation in impounded rivers will be interpreted more intuitively from a new vision, which could guide sluices ecological regulation schemes to realize their low environmental impact development.

项目针对当前多用单一换水率来反映整条河流水体交换能力的局限与不足，围绕如何明晰多闸坝河网水体交换能力的时空分异特征及其多源驱动机制、并揭示其定量水质效应这一核心科学问题；以水龄作为表征河流水体交换能力时空分异性的指标，以发展闸坝调控大型河网一、二维嵌套的水动力-水龄-水质数值模型为基础，通过模拟水龄水质时空变化及闸坝调控的影响，从更高的时空分辨率量化多闸坝河网水体交换能力的变化特征；针对河网水龄的多源特性，通过水龄的数值源解析，以河网水龄组分谱的变化作为表征，来量化干支流不同水源丰枯变化及闸坝调控对水体交换能力的影响，揭示其变化的多源驱动机制；在此基础上，进一步挖掘河流水质的时空变化与水龄及其组分谱之间的定量响应关系，揭示多闸坝河网水体交换能力对污染物输移变化的影响。成果可从更高的时空分辨率量化河流水体交换能力的变化，有望突破单一换水率反映整条河流水体交换能力的局限；同时可从新的视角直观理解变化环境下多闸坝河网水文水动力过程改变的水环境效应，能为科学制定闸坝生态水量调度方案提供依据。

科学量化闸坝等水利工程的水环境胁迫效应，是实现其低影响开发与运用的前提，是开展以恢复和改善河流水质为阶段目标生态调度的基础。水体交换能力既与流场密切相关又能从本质上量化流场在污染物与营养物输运中的作用，相比现场观测与常规的水动力水质模拟可以更直观的揭示水动力过程的环境效应。项目围绕如何通过闸坝调控来减轻其水环境胁迫这一核心问题，引入水龄作为表征河流水体交换能力时空变异性的指标，从一个新的视角研究闸坝调控下河流水文水动力过程变化的环境效应。本项目从流域的宏观尺度研究径流丰枯变化及闸坝调控对河流水量及溶质交换能力的影响，以长江上游高坝大库群控制的大型河网为研究区，基于可溶性物质平均水龄理论研发了多闸坝大型河网一、二维嵌套的水龄水质数值模型，包括金沙江和川江一维水龄水质数值模型、三峡库区二维水龄水质数值模型；量化了长江上游干支流水龄的沿程变化及在丰水期和枯水期的差异，从更高的时空分辨率明晰了多闸坝河网水体交换能力的时空分异特征；模拟了长江干流及雅砻江、岷江、沱江、嘉陵江、乌江等主要支流来水丰枯变化、溪洛渡、向家坝、三峡等大型水库调控对水龄的影响，量化了径流丰枯变化及闸坝调控对河流水体交换能力的影响，揭示了水龄变化的多源驱动机制。以氨氮和总磷为代表性水质因子，在长系列水龄水质连续数值模拟的基础上，分析了径流丰枯变化及闸坝调控对污染物输移的定量影响，提出了长江干流及三峡库区水质的时空变化与水龄及其组分谱之间的定量响应关系，揭示了多闸坝大型河网水体交换能力对污染物输移变化的影响。成果阐明了水体交换能力在闸坝调控下的定量变化及其多源驱动机制、以及相应的水质响应，从新的视角直观理解变化环境下多闸坝河网水文水动力过程改变的环境效应，可为科学制定闸坝生态水量调度方案提供依据。