杭州城西南排通道工程出口拟布置在钱塘江九溪岸段，为研究九溪岸段堤线优化对钱塘江防洪、御潮等功能的影响，采用平面二维数学模型，模拟了工程实施后钱塘江百年一遇大潮、百年一遇洪水期间沿线的壅水高度、流速变化等情况。数值计算结果表明，堤线优化后，当钱塘江遭遇百年一遇大潮时，工程区北岸堤前水位壅高相对明显，最大可达0.05m，南岸的水位壅高影响小于0.01m；南岸流速增加2%左右，但上下游岸段堤前水域流速变化不大。当钱塘江遭遇百年一遇洪水时，工程河段局部范围内水位壅高0.02m左右；下游相邻岸段堤前流速增加1～2%，南岸浦沿排灌站岸段流速增加2～3%，珊瑚沙水库围堤前沿流速影响较小。总体上，九溪岸段堤线优化对钱塘江防洪、御潮影响较小，对区域内地铁6号线、之江大桥、钱塘江大桥等涉水工程基本无影响。

Southwest drainage tunnel of Hangzhou City intended to be arranged in the Jiuxi reach of the Qiantang River. In order to study the influence of embankment line optimization on flood discharge and tidal bore of Qiantang River, 2-D mathematical model was established to study height of tidal bore and the variation of velocity along the river during spring tide and flood of Qiantang River once-in-a-century after the implementation of the project. Results from numerical model calculation showed that when Qiantang River encountered a spring tide once-in-a-century, relatively obvious raised water level in front of area in north embankment could be seen, the maximum was up to 0.05 m, increase of water level on the south embankment was less than 0.01 m, and the velocity of flow in the south embankment increased by about 2% after the embankment line was optimized. However, the velocity of the water in front of the embankment in the upper and lower reaches had little change. When the Qiantang River encountered a flood once-in-a-century, water level in the local area of the engineering reach increased about 0.02m. Velocity in front of the embankment downstream adjacent to embankment increased by 1%~2%, velocity increased by 2 %~ 3% along the south embankment in the reach of the Puyan drainage and irrigation station. The influence on velocity in the front of the embankment of the Shanhusha Reservoir was relatively small. On the whole, the optimization of embankment line in Jiuxi reach had little influence on flood discharge and tidal bore in Qiantang River, had no effect on the water wading projects such as Metro Line 6, Zhijiang Bridge and Qiantang River Bridge in the area.

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