Quantitative relationship between channels and bars in a tidal reach of the lower Yangtze River: Implications for river management

Abstract

Deep-water navigation channels in the tidal reaches of the lower Yangtze River are affected by water and sediment fluxes that produce complex shoals and unstable channel conditions. The Fujiangsha reach is particularly difficult to manage, as it has many braided channels within the tidal fluctuation zone. In this study, hydrologic and topographic data from the Fujiangsha reach from 2012 to 2017 were used to examine the variations in deposition and erosion, flow diversion, shoals, and channel conditions. Since the Three Gorges Dam became operational and water storage was initiated, the Fujiangsha reach has shown an overall tendency toward erosion. Channels deeper than 10 m accounted for 83.7% of the total erosion of the Fujiangsha reach during 2012-2017. Moreover, the dominant channel-forming sediments have gradually changed from suspended sediments to a mixed load of suspended and bed-load sediments. Deposition volumes of these sediments has varied significantly among different channels, but has mainly occurred in the Fubei channel. Furthermore, periodic variations in the Jingjiang point bar have followed a deposition-erosion-deposition pattern, and the downstream Shuangjian shoal mid-channel bar has been scoured and shortened. Approximately 44.0% of the bed load from the upstream Fujiangsha reach is deposited within the 12.5-m deep Fubei channel. The increased erosion and river flow from the Jingjiang point bar and the Shuangjian shoal during the flood season constituted 59.3% and 40.7%, respectively, of the total amount of siltation in the Fubei channel. Keywords: tidal current; fluctuating reach; point and central bar; channel conditions; quantitative relationship; lower reaches of the Yangtze River; Fujiangsha reach

Effect of water depth and waterway obstructions on the divergence and confluence areas of Dongting Lake and the Yangtze River after the operation of the Three Gorges Project

“…The Taipingkou waterway represents the Taipingkou diversion area reach, which has numerous point and mid‐channel bars in the waterway with strongly correlated evolution (Y. P. Yang, Zheng, Zhang, Zhu, Chai, et al, 2021; Zhao et al, 2020). After the TGP came into operation, water and sediment conditions changed significantly.…”

“…Considering the terrain in February 2014 as the basis for the verification of waterway conditions, the depth of the waterways from Yichang to Wuhan and Wuhan to Anqing reaches increased from 3.5 and 4.5 m to 4.5 and 6.0 m, respectively (Y. Yang et al, 2019). Moreover, the water depth of the estuary of the Yangtze River reached 12.5 m (Dai & Liu, 2013; Dai et al, 2018) and gradually extended to the Nanjing reach (Y. P. Yang, Zheng, Zhang, Zhu, Chai, et al, 2021). The complex relationship between changes in the hydrodynamics, sediment transport, and sandbank and tidal flats in the river–lake confluence area is significant, as it is a key river section for waterway management, dredging, and maintenance (Dong et al, 2020).…”

“…Yang et al, 2019). Moreover, the water depth of the estuary of the Yangtze River reached 12.5 m (Dai & Liu, 2013;Dai et al, 2018) and gradually extended to the Nanjing reach (Y. P. Yang, Zheng, Zhang, Zhu, Chai, et al, 2021). The complex relationship between changes in the hydrodynamics, sediment transport, and sandbank and tidal flats in the river-lake confluence area is significant, as it is a key river section for waterway management, dredging, and maintenance (Dong et al, 2020).…”

Experimental Study on the Local Scour of Submerged Spur Dike Heads under the Protection of Soft Mattress in Plain Sand-Bed Rivers

“…Effective methods of calculating methods to reach the biggest local scouring depth near the submerged spur dike and distance under conditions of bottom protection have not been established. (2) This paper adopts the undistorted model experimental research method and studies the corresponding relationships among the maximum depth of local scouring and the form of the submerged spur dike head, relative dam height, width of bottom protection, force condition of the incoming flow and longitudinal slope of the dam head. Our findings suggest that the relationships between relative dam height, the force of the incoming flow and scouring depth and distance can be expressed by a power relation, whereas the relationships between the width of the bottom protection, longitudinal slope of the dam head and scouring depth and distance can be expressed by an exponential relation.…”

“…The smooth operation of waterways has promoted the development of a green economy. To continuously improve waterway levels, it is usually necessary to adopt structures such as spur dikes, longitudinal dams and lock dams to renovate obstruction sections [1,2]. As a typical regulating structure of water conservancy and waterway engineering, a spur dike functions to narrow the width of a river, adjusting water flow and protecting shoals; it is widely applied in projects of river shoal protection, waterway regulation and subgrade protection [3,4].…”