电站调峰作用下的澜沧江下游水动力及底栖动物变化规律

Hydropower is the most reliable and cost-effective source of energy. The energy is produced with a high flexibility in generation output and can be used both for base load and peak energy demand. The flex usage of hydropower becomes more important as the increased electric energy is produced from unsteady wind and solar based power. However, using this flexibility will give more rapid and frequent discharge fluctuation than under natural hydrological conditions or conventional use of hydropower. Consequently, the habitat factors of velocity, water depth, water temperature and sediment are changed accordingly. The biomass, density and type of macroinvertebrates are also altered. The proposal focuses on the hydrodynamics of hydropeaking flow and the impact on macroinvertebrates in the lower reach of the Langcangjiang River where several dams are constructed. First, the flow characteristics are investigated based on observations of velocities, water stages and water temperatures and simulations of hydropeaking flows with numerical methods. Second, the impact of hydropeaking on the distribution of macroinvertebrates will be studied based on field samplings and observation and the underlying mechanics will be investigated using flume experiments. Finally, a habitat suitability model for dominant macroinvertebrates in study area will be developed and tested by the observed data and experimented data and it will be integrated into thermal-hydrodynamic model. This study will be very helpful to the development of the ecological hydraulics and will provide a powerful technical support for protection and regulation of ecology in southwestern rivers.

水电不仅为电网提供稳定的基础负荷，还在电网调峰中发挥着重要的作用。随着清洁能源的增加，水电调峰的作用越来越突出。然而，电网调峰会引起下游河道流量的急剧变化，流速、水深、水温、泥沙等生境要素随之改变，进而影响大型底栖动物的种类、密度和生物量。本项目以澜沧江下游的梯级电站河段为研究对象，现场观测流速、水位、水温的变化，建立调峰水流的数值模型，揭示调峰水流的动力特征。通过野外采样，探究澜沧江下游的底栖动物分布特征，分析调峰水流对底栖动物的影响规律；建立可控实验平台，研究水流变化对底栖动物的影响机制。集成野外采样和可控实验的实验数据，建立底栖动物（密度、多样性）与生境因子的适宜性关系模型，结合水动力模型，构建澜沧江下游的生境模型。本项目的研究对于生态水力学的发展具有重要的学术价值，对于西南河流的管理和保护具有重要的参考价值和指导意义。

调峰水流（hydropeaking）指由于电网调峰而导致的水电站非恒定泄流，相对于自然水流，它变幅更大、变速更快、变频更高，影响流速、水深、水温、底质等生境要素的变化，进而影响水生生物的空间分布。项目以澜沧江下游的景洪水电站-关累断面（全长80km）为研究区域，，研究了调峰水流的时空变化规律和动力特征，揭示了调峰水流对底栖动物的影响机制，剖析了紊流中底栖动物的运动特征并建立了生境模型。主要成果包括： .（1）调峰水流的时空变化规律和动力特征。利用一维河道水动力-水温模型，模拟了调峰水流的流量、水位、水温的传播过程，分析了调峰水流对水深等生境要素的影响。模拟了调峰水流的流场分布，发现流量下降阶段可能出现回流现象；采用不同形式的粗糙元，模拟河床底质条件的变化，分析了底质粗化对紊动能和剪切力的影响。.（2）调峰水流对底栖动物的影响规律。通过采样鉴定发现，澜沧江的大型底栖动物以水昆虫为主，干流采样点的底栖动物密度从上游到下游逐渐增大，和调峰水流强度负相关。以钩虾属和扁蜉属为对象，野外观察它们在各种生境条件下的漂移昼夜节律，研究了流量脉冲对底栖动物的影响，结果表明：流量扰动下的钩虾属漂移强度变化明显，漂移密度显著性提升，扰动期间漂移密度峰值出现的时刻集中在流量扰动的1小时之后。.（3）紊流中底栖动物的运动特征和生境模型。利用粒子运动的拉格朗日模型，研究了不同位置底栖动物的起漂特性：起漂和瞬时剪切力有关，多发生在猝发过程的清扫阶段；利用紊流的统计理论，定量确定了紊流中底栖动物的下沉速度，紊流中的下沉速度最大折减60%。采用广义相加模型，建立底栖动物对流速、水深、底质的适宜度模型。.项目发表论文9篇，培养研究生5名，参加国际会议4人次，研究成果以河床剪切力为纽带，系统揭示了流速变化、底质粗化等生境要素对底栖动物起漂的动力学机制，深刻刻画了水流变化对水生生物影响的路径，可望支撑供西南地区河流健康和流域生态保护。