青草沙水库工程对附近水域河床冲淤的影响

Impact of Qingcaosha reservoir project on the bed erosion and deposition nearby the water area

青草沙水库是长江河口的一个重大工程,显著改变了北港上段的河势。河势的变化会引起流场和泥沙质量浓度的变化,进而影响河床的冲淤。本文应用三维水动力和泥沙数值模式,计算和分析了青草沙水库工程对附近水域流场、泥沙质量浓度和冲淤的影响。青草沙水库工程建设后,北港河道束窄,导致水库北侧河道主槽流速和泥沙质量浓度增加。水库工程使得进入北港的径流量和纳潮量减少,导致青草沙水库以东、北港下段和拦门沙区域流速和泥沙质量浓度下降。应用半理论半经验河床冲淤公式和模式计算的工程前后流速、泥沙质量浓度和水位数据,给出了由水库工程造成的河床冲淤变化分布。在水库以北北港水域发生普遍冲刷,冲刷强度最大可达2-3m,冲淤分布和量值与工程前后实测水深变化吻合良好。数值模式较好地模拟了青草沙水库工程对附近水域冲淤分布的影响和变化量值。

As a major project lying in the Changjiang Estuary,Qingcaosha reservoir leads to change of river regime in the North Channel markedly.The change of river regime could induce change of current field and sediment concentration,and then influence bed erosion and deposition.The three-dimensional hydrodynamic and sediment model were used to calculate and analyze the impacts of the project on current filed,sediment concentration,erosion and deposition in area around the reservoir.After the project,width of upper reaches of the North Channel was narrowed,which results in increase of both current speed and sediment concentration in the major channel on the north of Qingcaosha reservoir.On the contrary,the current speed and sediment concentration decrease in areas on east of the reservoir,lower reaches of the North Channel and sand bar due to the decrease of river discharge and tidal prism flowing into the North Channel.Using the formula of bed erosion and deposition based on experience and theory,and the modeled current,sediment concentration and water level,the erosion and deposition caused by reservoir project was calculated.Strong erosion occurs in the North Channel on north of reservoir,with maximum of 3m,which matches well both in shapes and values with the observed depth change before and after the project.The numerical model simulated the distributions and magnitude of bed erosion and deposition fairly well caused by Qingcaosha reservoir project.