由于永定河流域内的水量减少,水资源短缺,该段河道已经干涸,甚至出现沙化情况,挖沙造成河床上存在大大小小的砂石坑。20世纪70年代以来,北京市把永定河主要作为泄洪河道,忽视了其生态涵养和城市景观的作用,使得永定河及沿岸的生态环境逐步恶化,需要进行生态治理。根据永定河卢三段的设计原则和目标,通过二维水动力学模型,计算了主河道流速分布、河道走势情况,分析大洪水条件下对生态工程、堤防的冲刷破坏情况。结果表明,河道内的砂石坑,对卢三段的流速和流势以及对行洪安全影响很大。 Due to the reduction of water volume in the Yongding River Basin and the shortage of water resources, the river section of this section has dried up and even desertification has occurred. Dredging sand causes large and small gravel pits in the riverbed. Since the 1970s, Beijing mainly used the Yongding River as a flood releasing channel, neglecting its ecological conservation and urban landscape. As a result, the ecological environment in the Yongding River and the coastal areas deteriorated gradually and ecological management was needed. According to the design principles and objectives of Section 3 of Yongding River, the velocity distribution of the main channel and the trend of the channel are calculated by two-dimensional hydrodynamic model, and the erosion and damage to the ecological engineering and the embankment under the condition of flood are analyzed. The results show that the gravel pits in the river channel have a great influence on the flow velocity and flow of the Lusan Section and the safety of flood discharge.