径流量变化对长江口水动力特性的影响

为了研究径流量变化对长江口水动力特性的影响,利用MIKE21建立长江口水动力数学模型,分别模拟计算长江口不同径流量影响的潮流场,统计分析不同径流量时各汊道涨落潮量和净泄量以及分配比例;统计分析不同径流量对各汊道潮位变化的影响;统计分析不同径流量对北槽中下段水动力特性的影响。得到如下结论:1)径流量的变化对于涨潮分流的影响显著,随着径流量的增加,更多的潮流从北支、北港、南槽进入长江口内。当上游的径流动力增强,外海潮流受上游径流的阻挡,难以继续上溯。2)越是靠近上游,径流量的变化对平均潮位的影响程度越高,入海口处受径流的影响微弱;上游径流量越大,潮波向内陆传播越受阻,能量消耗越大,致使其动力减弱。3)径流量的变化对平均流速的影响与上述潮位变化类似,上游径流量越大,各汊道流速越大;越靠近海洋,径流影响越小。4)长江口北槽中下段转流时刻会出现平面对流现象。横向方向上普遍存在越堤水流,且南北导堤均为北向越堤流占优势。

Effect of runoff change on hydrodynamic characteristics of the Yangtze River estuary

A hydrodynamic mathematical model of the Yangtze River estuary is established by using the MIKE21 to study the effect of runoff change on hydrodynamic characteristics of the Yangtze River estuary. The tidal current fields of the Yangtze estuary with different runoffs are simulated. The amount of the flood current, ebb current and the net water leak with different runoffs is counted and analyzed. And the effect of runoff change on tidal level and hydrodynamic characteristics of the North Passage is analyzed. The results are as follows:1) The change of runoff has a significant impact on the flood diversion. With the increase of the runoff, more and more tidal current flows into the Yangtze estuary from the North Branch, the North Channel and the South Passage. When the upstream runoff power increases, the tidal current is blocked by the upstream runoff, and it is difficult for it to continue upstream. 2)The closer it is to the upstream, the higher the impact of runoff change on the average tide level is, and the impact of runoff at the estuary is weak. The larger the upstream runoff is, the more blocked the tide wave propagating inland is, the more the energy consumes, resulting in the weakening of its power. 3) The effect of changes in runoff on average velocity is similar to that of the changes in tidal level described above. The greater the upstream runoff, the greater the velocity of each channel. 4) Plane circulation will occur at the turning time in the middle and lower part of the North Passage of the Yangtze River estuary. Levee crossing flow is common in the transverse direction and both north and south diversion dikes are dominated by the north levee crossing flow.