黄河上游梯级水库运行的生态影响研究

为科学揭示梯级水库群运行对河流生态的影响,基于黄河上游实测水沙序列,采用IHA(Indicators of Hydrologic Alteration)指标体系,对比分析了不同工程运行时期黄河上游水文情势变化,运用多系列贡献率分割法,量化了不同影响因子对水文情势变化的贡献率。通过输沙率法结合断面淤积形态分析揭示了黄河上游河道冲淤演变。结果表明,黄河上游水库运行对河流径流及河道形态产生了深刻影响,进而影响了河流生态。水库运行后非汛期月均流量上升、汛期月均流量下降、高流量事件发生频率与流量减少,径流趋于平缓,且宁蒙河段泥沙淤积、断面形态趋于宽浅。分析表明水库运行是造成黄河上游兰州水文情势变化的主要原因,以及石嘴山、头道拐水文情势变化的重要原因,高流量事件的减少加剧了河道淤积,使河流生态朝不利方向演化,为维护黄河上游生态健康有必要实施生态调度,提高涨水期和洪水期下泄流量并制造高流量事件。研究为评估梯级水库运行的生态影响、指导梯级水库生态调度提供方向性参考。

Research on ecological impacts of the joint operation of cascade reservoirs in the upstream of the Yellow River

Aiming to reveal the impacts of the joint operation of cascade reservoirs on riverine ecosystems, this study adopts Indicators of Hydrologic Alteration (IHA) to analyze hydrologic alterations in the upstream of the Yellow River in different reservoir operation periods which is based on long-term measured flow data. A multi-series contribution rate division method is developed to quantify the influences of different factors. Sediment transport rate method and cross-section deposition patterns analysis are used to show the erosion and deposition in the upstream of the Yellow River using long-term measured sediment data. The results show that reservoir operation has significant ecological impacts on both runoff and sediment transport which have been altered dramatically. The runoff has become steadier after reservoir operation:the monthly average flow has increased in the non-flood season while decreased in the flood season; the frequency and magnitude of high flow events has declined. Moreover,sediment deposition has become more and more serious in the Ningxia-Inner Mongolia reach. Besides,the typical cross-section has become wider and shallower. This study proves that reservoir operation is the most important cause of the hydrologic alterations in Lanzhou, and it is also an important cause in Shizuishan and Toudaoguai. It is revealed that the decrease of high flow events has aggravated the channel sedimentation, which can impose negative ecological impacts on this river. For better conservation of river health, it is necessary for reservoirs in the upstream of the Yellow River to adopt ecological operation, increasing water release in the rising-water season and flood season and creating high flow events. This study provides important information to the ecological impacts assessment of the joint operation of cascade reservoirs and the ecological operation of cascade reservoirs.