Study on the impact of upstream discharge on saltwater intrusion distance in the Yangtze Estuary
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摘要: 长江口盐水入侵严重影响上游供水安全、农业灌溉和生态环境健康,其中在径流和潮动力的相互作用下盐水上溯距离一直受到较多的关注,然而径潮相互作用下盐水上溯距离研究并不充分。本文利用MIKE 3水动力学模型建立了长江口三维水动力和盐度数学模型,采用2016年长江口实测潮位、流速、流向和盐度资料对长江口三维水动力和盐度数学模型进行了验证,验证结果显示模拟值和实测值较为吻合,表明本文所建立的长江口三维水动力和盐度数学模型可以较好的模拟长江口附近的水动力和盐度特性。为了探究上游径流对长江口盐水上溯距离的影响,本文设置了长江口上游
15000 −50000 m3/s中8个径流量,分别模拟研究了上游不同径流量对长江口南支-北港、南支-南港-北槽和南支-南港-南槽三条航道盐水入侵上溯距离的影响。模拟结果表明,三条航道的盐水入侵程度显著依赖于潮汐动力,大潮潮动力强,外海与北支盐水倒灌的盐水入侵都强于小潮期间,盐水上溯距离整体大于小潮期间。当径流较低时,北支存在盐水倒灌现象,也会增加盐水入侵距离。同时分析了不同径流条件下三条航道盐度垂向分布和层化现象,并分别建立了上游径流量和三条航道盐水上溯距离的相关关系。研究结果可对长江河口“压咸补淡”和物质输运等研究提供一定的参考。Abstract: Saline water intrusion at the Yangtze River Estuary severely affects the security of upstream water supply, agricultural irrigation, and ecological environmental health. The distance of saline water intrusion upstream, influenced by the interaction between runoff and tidal forces, has received considerable attention. However, research on the extent of this intrusion under the influence of the runoff-tide interaction remains insufficient.This paper establishes a three-dimensional hydrodynamic and salinity mathematical model of the Yangtze River Estuary using the MIKE 3 hydrodynamic model. The model is validated against field measurements of water levels, flow velocities, flow directions, and salinity from the Yangtze River Estuary in 2016. The validation results show a good agreement between the simulated and measured values, indicating that the three-dimensional hydrodynamic and salinity mathematical model of the Yangtze River Estuary established in this study can effectively simulate the hydrodynamic and salinity characteristics in the vicinity of the estuary.To investigate the impact of upstream runoff on the extent of saltwater intrusion in the Yangtze River Estuary, this study sets up eight different flow rates ranging from 15,000 to 50,000 m3/s for the upstream section of the Yangtze River Estuary. The simulations focus on the effects of these varying upstream flow rates on the saltwater intrusion distances in three navigation channels: the South Branch-North Port, the South Branch-South Port-North Channel, and the South Branch-South Port-South Channel. The simulation results indicate that the degree of saltwater intrusion in all three channels is significantly dependent on tidal dynamics. During spring tides, when tidal forces are stronger, both the seawater backflow into the North Port and the saltwater intrusion into the North Branch are more pronounced compared to neap tides, resulting in longer saltwater intrusion distances overall during spring tides. When the upstream discharge is low, backflow from the North Branch also contributes to increased saltwater intrusion distances.The vertical distribution of salinity and stratification phenomena in the three channels under different flow conditions were also analyzed, and the relationships between upstream flow rates and the distances of saltwater intrusion in the three channels were established. The findings of this study provide valuable references for research on "salinity control and freshwater supplementation" in the Yangtze River Estuary, as well as studies on material transport. -
图 7 不同径流量条件下大潮期间不同时刻三条航道盐度垂向分布(南支-北港:
15000 m3/s(a),50000 m3/s(b);南支-南港-北槽:15000 m3/s(c),50000 m3/s(d);南支-南港-南槽:15000 m3/s(e),50000 m3/s(f))Fig. 7 Vertical Salinity Distribution at Different Times during Spring Tides under Various Discharge Conditions in Three Channels (the South Branch-North Port:
15000 m3/s (a),50000 m3/s (b).the South Branch-South Port-North Channel:15000 m3/s (c),50000 m3/s (d). the South Branch-South Port-South Channel:15000 m3/s (e),50000 m3/s (f))图 8 不同径流量条件下小潮期间不同时刻三条航道盐度垂向分布(南支-北港:
15000 m3/s(a),50000 m3/s(b);南支-南港-北槽:15000 m3/s(c),50000 m3/s(d);南支-南港-南槽:15000 m3/s(e),50000 m3/s(f))Fig. 8 Vertical Salinity Distribution at Different Times during Neap Tides under Various Discharge Conditions in Three Channels (the South Branch-North Port:
15000 m3/s (a),50000 m3/s (b).the South Branch-South Port-North Channel:15000 m3/s (c),50000 m3/s (d). the South Branch-South Port-South Channel:15000 m3/s (e),50000 m3/s (f))表 1 模型参数
Tab. 1 Model parameters
模型参数 配置 流量边界 逐日实测时间序列文件 潮位边界 TPXO8获取 粗糙度高度 0.003~0.005 m 水平涡流粘度 0.28 水平扩散比例因子 0.28 垂向扩散比例因子 0.1 盐度边界(上游/下游) 0 / 32 表 2 大潮和小潮期间径流量和盐水上溯距离对应关系
Tab. 2 Relationship between Discharge and Salt Water Intrusion Distance during Spring and Neap Tides
流量Q(m3/s) 大潮期间盐水上溯距离L (km) 小潮期间盐水上溯距离L (km) 南支-北港 南支-南港-北槽 南支-南港-南槽 南支-北港 南支-南港-北槽 南支-南港-南槽 15000 140(69+71) 136(66+70) 132(66+66) 134(69+65) 129(67+62) 128(67+61) 20000 137(57+80) 115(50+65) 112(50+62) 104(41+63) 73 78 22500 102(44+58) 73(18+55) 69(18+51) 70(13+57) 49 42 25000 89(33+56) 53 45 41 39 40 27500 72(20+52) 51 43 29 39 39 30000 44 49 41 28 38 39 40000 35 46 38 26 35 38 50000 33 46 34 24 32 36 注:括号内分别为北支盐水倒灌距离与外海盐水入侵距离,括号外为两者距离之和。 -
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