八卦洲汊道改善分流比工程措施研究

Preliminary studies on improvement measures to the diversion ratio of Nanjing Baguazhou branch

自20世纪30年代开始,因上游河势的变化,南京八卦洲汊道左汊逐渐从主汊演变成支汊.近年来,随着来水来沙条件的改变,左汊衰退速率又有所加快,并已多次观测到12%左右的分流比.为此,迫切需要采取工程措施,遏制八卦洲左汊缓慢衰退的趋势.针对选用的组合工程措施,运用物理模型试验、MIKE21等水动力数学模型研究手段,对八卦洲水位、流速、左右两汊分流比进行了数值模拟,并主要分析了导流坝、切滩、疏浚及其组合工程措施对分流比的改善.结果表明:导流堤的分流效果较好,组合工程措施最大可增加左汊分流比4.76%.通过与物理模型试验结果的比较,为整治工程的实施提供相应的理论依据,并为工程进一步改善提出了建议.

Due to changes in upstream conditions since 1930s, the left branch of Baguazhou inlet has been gradually evolving from the main river branch to the subsidiary channel. In recent years, since the variation of discharge and sediment concentration, the rate of decay of the left branch has accelerated again, with diversion ratios as low as 12% observed repeatedly. For this reason, engineering treatments are urgently required to curb the recessionary trend of the left branch. According to the engineering measures, a physical model and MIKE21 hydrodynamic numerical model are used to simulate the water level, flow rate, and diversion ratio of the Baguazhou inlet. The improvement effects on the diversion ratio of a diversion dam, cutting of the beach, dredging, several separate schemes and combined schemes are mainly analyzed. The analysis results show that the diversion effect of the diversion dam is quite good and combined regulation works can increase the left branch diversion ratio by as much as 4.76%. By comparison with the physical model, it provides a theoretical basis for the implementation of the regulation works and gives suggestions for further improvement of the regulation works.