On the mechanism behind the shift of the turbidity maximum zone in response to reclamations in the Yangtze (Changjiang) Estuary, China
On the mechanism behind the shift of the turbidity maximum zone in response to reclamations in the Yangtze (Changjiang) Estuary, China
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DOI：
10.1016/j.margeo.2021.106569
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发表时间：
2021-10
期刊：
影响因子：
2.9
通讯作者：
Lizhi Teng;Heqin Cheng;H. Swart;P. Dong;Zhanhai Li;Jiufa Li;Yajun Wang
中科院分区：
文献类型：
--
作者：
Lizhi Teng;Heqin Cheng;H. Swart;P. Dong;Zhanhai Li;Jiufa Li;Yajun Wang
河口围海造地会极大地改变河道的几何形状和水动力条件，这些变化可能会对最大浑浊带的时空分布产生重大影响。本研究主要探讨2007-2018年长江口北槽大面积围填海的影响及最大浑浊带沿着的行为。利用2006 - 2019年枯水期6幅Landsat遥感影像，获取了北港水深、佘山站潮位、大通站流量和浊度等数据。在2003年和2018年旱季获得了流速和悬浮泥沙浓度的现场测量数据。数据分析表明，填海导致河道变窄（0.86-2.74公里）和固定，造成深河道侵蚀0.19-3.72米，并在潮滩上沉积。此外，它被发现，最大浑浊带的长度减少：其向陆地边界移动5公里，在大潮和小潮在旱季向海17公里。向海边界的位置在3 km范围内徘徊，小潮时比大潮时更靠下游。最大浑浊带的边界变化的概念模型，在响应填海。围垦工程后，河道变深变窄，加剧了流速的落潮优势。床沙粗化减弱了再悬浮作用，降低了底潮平均悬沙浓度。这些变化导致了潮汐平均悬浮泥沙浓度的深度平均值显着下降，并导致最大浑浊带的向陆边界的向海移动。
Reclamation in estuaries can greatly change the channel geometry and hydrodynamic conditions and these changes may have significant impacts on spatial and temporal distribution of the turbidity maximum zone. This study focuses on the effects of a large area of reclamation built in 2007–2018 and the behavior of the turbidity maximum zone along the North Channel of the Yangtze Estuary. Data were collected of bathymetry in the North Channel, tidal elevations at Sheshan Station, river discharge at Datong Station and turbidity, retrieved from six Landsat remote sensing images in the dry season from 2006 to 2019. In-situ measured data on flow velocity and suspended sediment concentration were obtained in the dry season of 2003 and 2018. Analysis of the data revealed that reclamations, which led to narrowing (0.86–2.74 km) and fixing of the channel, caused erosion of 0.19–3.72 m in the deep channel and deposition on the tidal flats. Furthermore, it was found that the length of the turbidity maximum zone decreased: its landward boundary shifted 5 km seaward during spring tide and 17 km seaward during neap tide in the dry season. The position of the seaward boundary wandered within a range of 3 km, being further downstream during neap tide than that during spring tide. A conceptual model of changes in the borders of the turbidity maximum zone in response to reclamation is proposed. After the reclamation works, the deeper and narrower channel intensified ebb-dominance of the flow velocity. The coarsening of bed sediment weakened resuspension and decreased the bottom tidally averaged suspended sediment concentration. These changes led to a significant decline in the depth-mean of tidally averaged suspended sediment concentration and caused the seaward movement of the landward boundary of the turbidity maximum zone.