Characterizing the circulation flow structure in the Modaomen Estuary of the Zhujiang River
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摘要: 河口环流结构关系到物质输运、泥沙沉积和地貌变化等物理过程。根据2019年磨刀门河口原型观测平台洪枯季连续观测分层潮流资料，统计洪枯季、大小潮河口东、西汊的涨落潮流及历时变化特征，利用理论方法解析河口东西汊平面环流和重力环流结构，进一步引入混合参数研究河口纵向环流中的潮汐应变环流。研究发现枯季东、西汊在转潮时刻存在东涨西落的平面环流结构，洪季平面环流特征较不明显；枯季重力环流强度整体略大于洪季，西汊重力环流强于东汊，表层向海环流流速可达0.2～0.25 m/s，而底层向陆环流流速相对较小。洪季大潮期由潮不对称性驱动的潮汐应变环流相对较大，进而增强了纵向环流的强度。河口垂向余流结构同样表现洪枯季、大小潮的变化规律。洪季余流整体较大，西汊在小潮期表层余流流速超过0.6 m/s，而东汊余流则明显呈现表层向海、底层向陆的分布特征，枯季余流整体较小，表明其对物质输运和河口地形塑造作用较弱。Abstract: The structure of circulation flow is related to physical processes such as material transport, sediment deposition and landform evolution. According to the continuous stratified tidal current data derived by the prototype observation platform of Modaomen Estuary in flood and dry seasons in 2019, the flow characteristic during the spring and neap tide at wet and dry seasons in the east and west branches were analyzed. Theoretical methods were used to explore plane circulation and gravity circulation structure in the east and west branches. Besides, the longitudinal circulation with the tidal strain circulation was explained by the mixed parameter. Plane circulation flow structure with ebb at west branch and rise at east branch during the dry season was found. Moreover, gravitational circulation at dry season was generally larger than that at wet season, and the gravitational circulation at west branch was stronger than the east branch, with 0.2–0.25 m/s surface velocity and much lower bottom velocity. The tidal strain circulation driven by the tidal asymmetry at wet season spring tide was relatively higher, which tends to favor the magnitude of vertical circulation. Additionally, the muti-layer residual current also displays seasonal and tidal variations. The residual current at wet season was relatively larger than the dry season, with the surface residual flow velocity more than 0.6 m/s during the neap tide at west branch. However, the downstream residual current at surface and upstream residual current at bottom was found at east branch. Much lower residual current velocity was found at dry season, indicating that the impact on the substance transport and morphological evolution was lower.
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图 2 珠江河口原型观测平台站点位置
Fig. 2 The location of the prototype observation platform in the Zhujiang River Estuary
图 3 2019年6月（洪季）（a）和10月（枯季）（b）东、西汊流速流向和潮位特征
Fig. 3 The characteristic of flow velocity, direction and tidal level at east and west branches in June (flood season) (a) and October (dry season) (b) 2019
图 4 洪枯季涨落潮流速、历时差异
Fig. 4 The flood and ebb tide flow, duration difference at wet and dry seasons
图 5 平面环流的时空分布特征
Fig. 5 Temporal and spatial distribution characteristic of the plane circulation
图 6 重力环流时空变化特征
Fig. 6 Temporal and spatial variations characterisitic of gravity circulation
图 7 垂向河口余流的时空变化特征
Fig. 7 Temporal and spatial variations characteristic of vertical residual flow
表 1 测站位置表
Tab. 1 The field measured sites
测站 纬度 经度 水深/m A8 22°04′35.98″N 113°28′13.01″E 6 A9 22°03′28.70″N 113°34′35.28″E 3 A10 22°02′14.99″N 113°31′59.00″E 4.2 
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表 2 珠江口原型观测站磨刀门水域测站平均流速和流向
Tab. 2 The statistical data of average flow velocity and direction at Modaomen based on the prototype observation platform in Zhujiang River Estuary
测站 潮型 全年 枯季 洪季 流速/
（m·s−1）流向/
（°）流速/
（m·s−1）流向/
（°）流速/
（m·s−1）流向/
（°）A8 落潮 0.51 154 0.48 155 0.53 153 涨潮 0.27 334 0.29 334 0.24 337 A9 落潮 0.29 146 0.26 152 0.31 141 涨潮 0.2 293 0.2 294 0.21 292 A10 落潮 0.43 196 0.39 204 0.45 191 涨潮 0.23 350 0.26 334 0.22 367 平均 落潮 0.41 165 0.38 170 0.43 162 涨潮 0.23 326 0.25 321 0.22 332
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