基于复合模式动边界的鄱阳湖水利枢纽工程对湖泊水文情势与富营养化影响的模拟研究

Poyang Lake is the largest fresh-water lake in China, and also is one of two large river-connecting lakes in Changjiang River network. It plays an important role in the regulation of floods and the conservation of biological diversity and other special ecological function.The proposed Poyang Lake Water-Control Project(PLWCP) will hamper the continuity and liquidity of natural river-lake system to some extent. Flow regime change in river-lake system is the main driving force of evolution of river-lake ecosystems. In order to assess the impacts of PLWCP on lake hydrodynamic and eutrophication, a two-dimensional Poyang Lake Hydrodynamic and Eutrophication Modeling System will be developed based an integrated method to deal with complecated moving boundary due to both high amplitudes of water level natural changes in shallow lakes and the processes of storing-water and dewatering of PLWCP. For this issue, based on the analysis on characteristics of water level and morphological structure and hydrological characteristics of Poyang Lake, the moving inflow boundary conditions will be presented and to be added to moving boundary conditions in the existing hydrodynamic models, in which the number of inflows and the positions of inflow points are unchanged. In sensitive areas and key areas more sampling points will be added in order to get representatively two-dimensional hydrodynamic and nutrient data. After the implement of calibration and validation with those in situ data, the impacts of PLWCP on hydrodynamic and eutrophication, which includes two-dimensional flow, perennial backwater area, fluctuating backwater area, water exchange period, water-level rhythm changes in sensitive area and key area, wetland changes in nature reserve, will be assessed with the model throght using these methods of sensitivity simulation and scenario simulation on the basis of single factor and combined multi-factors. In the design of sensitivity simulation and scenario simulation, both operations of Three-Gorges Reservoir and PLWCP will be taken into consideration.In addtion, the research will reveal the quantitative changes of river-lake relation resulted from PLWCP in the basis of analysis of simulated results from perspective of the fluxes of water and nutrient. Quantitative analysis the impacts and its control-mechanism of PLWCP on lake hydrodynamic and eutrophication.

拟建的鄱阳湖水利枢纽工程在某种程度上将影响江湖系统长期形成的生态适应性。水文情势变化是江湖生态系统演变的主要驱动力。针对鄱阳湖水位高动态的自然节律变化和水利枢纽工程蓄排水过程的人工节律变化所导致的特殊动边界问题，引进动态入流边界条件，构建“高水位湖相型”和“中低水位河相型”两种形态结构自然转换并能进行长期连续模拟的动力学模型；采用敏感区域和重点区域水动力与营养盐要素加密布点的实测方案，建立基于复合模式动边界的鄱阳湖二维水动力与富营养化模型；通过敏感性模拟和情景模拟，在三峡工程运行调度背景下，探讨鄱阳湖水利枢纽工程对鄱阳湖流场、常年回水区和变动回水区、换水周期、敏感区域和重点区域的水位节律变化和自然保护区湿地淹水频率时空变化的影响；从水及营养盐等物质通量时空变化角度，揭示鄱阳湖水利枢纽工程引起的江湖关系量化改变；定量分析鄱阳湖水利枢纽工程对鄱阳湖水文情势与富营养化的影响与调控机制。

拟建的鄱阳湖水利枢纽工程在某种程度上将影响江湖系统长期形成的生态适应性。水文情势变化是江湖生态系统演变的主要驱动力。针对鄱阳湖水位高动态的自然节律变化和水利枢纽工程蓄排水过程的人工节律变化所导致的特殊动边界问题，构建了“高水位湖相型”和“中低水位河相型”两种形态结构自然转换并能进行长期连续模拟的动力学模型；通过典型年份模拟和情景模拟，在三峡工程运行调度背景下，阐明了鄱阳湖水利枢纽工程作用下湖泊水位、流场、流量以及换水周期的定量变化、敏感区域和重点区域的水位节律变化和自然保护区湿地淹水频率时空变化；枢纽工程不仅将降低湖泊流速，如湖泊北部流速降幅大于40%，也将导致实际控水期间换水周期的增幅在27%～53％之间；枢纽工程导致重力型基本湖流减少、顶托型基本湖流增加和局部湖流改变的现象；水利枢纽工程对江湖关系改变的可能性及对长江干流流量的影响分析，结果表明在一个枢纽工程水位调度周期中，湖泊外排到长江的径流总量无枢纽与有枢纽的差异很小，基本维持了整个水位调度周期的水量平衡，但在一定程度上改变了湖泊外排长江水量的时间，使不同年型丰水期的湖泊外排水量有所减少，低枯水期的湖泊外排水量有所增加；枢纽工程对湖泊富营养状态的影响作用不明显，且由于枢纽蓄水量增加，使湖泊库容增加，导致湖泊的环境容量增加，反而使湖泊的富营养状态有所改善，如分析表明无论是枯水年还是丰水年，枢纽蓄水期间有枢纽情景的富营养、磷限制潜在性重富营养和磷中等限制潜在性重富营养的面积占比都有所下降，而中营养的面积占比有所增加，但增加的绝对面积都不大。定量分析了鄱阳湖枢纽工程的利弊，鄱阳湖水利枢纽工程对湖泊旱情有一定的缓解作用，主要对松门山以北的入江水道和松门山附近的旱情有较大的缓解作用，对吴城和南矶2个国家湿地自然保护区核心区，以及棠荫以南和5河入口区域的旱情缓解作用有限。指出了目前水利枢纽工程调度方案存在的问题及其可能的优化方案。