Alternate erosion and deposition in the Yangtze Estuary and the future change

Abstract

The morphological changing trend of the Yangtze Estuary, the largest estuary of Asia, has become a focus of research in recent years. Based on a long series of topographic data from 1950 to 2015, this paper studied the erosion-deposition pattern of the entire Yangtze Estuary. An alternation between erosion and deposition was found during the past 65 years, which was in correspondence to the alternation between flood and dry periods identified by multi-year average duration days of high-level water flow (defined as discharge ≥ 60,000 m 3 /s, namely, D ≥60,000) from the Yangtze River Basin. A quantitative relationship was further developed between the erosional/depositional rate of the Yangtze Estuary and the interpreting variables of yearly water discharge, D ≥60,000 and yearly river sediment load, with contributing rates of 1%, 59% and 40%, respectively. Mechanism behind the alternate erosion and deposition pattern was analyzed by examining residual water surface slope and the corresponding capacity of sediment transport in flood and dry periods. In flood periods, a larger discharge results in steeper slope of residual water level which permits a greater capacity of sediment transport. Therefore, more bed materials can be washed to the sea, leading to erosion of the estuary. In contrast, flatter slope of residual water level occurs in dry periods, and deposition dominates the estuarine area due to the decreased capacity of sediment transport and the increased backwater effect of flood-tide. Coastal dynamics and estuarine engineering projects alter the local morphological changes, but slightly affect the total erosional/depositional rate of the whole estuarine region. Heavy sedimentation within the Yangtze Estuary after the impoundment of the Three Gorges Dam can be attributed to the

Modeling the Morphodynamic Response of Estuarine Intertidal Shoals to Sea‐Level Rise

“…Also, in real case studies, there could be other simultaneous and ongoing morphological adaptations with different time scales (decadal to geological) that could influence the SLR adaptation. Around the world, estuaries and tidal basins are subjected to dredging activities (Depreiter et al., 2013), land reclamation (MacKinnon et al., 2012), subsidence (Fokker et al., 2018), and changes in the tidal regime (Eelkema et al., 2013), varying riverine discharges, and sediment supply (Jaffe et al., 2007; Portela, 2006; B. Zhu et al., 2020). Also, other systems are still infilling and not in equilibrium (e.g., de Haas et al., 2018; van der Spek, 1994).…”

Seasonal Variation of Catenary-Bead Dunes in the Yangtze River Estuary: Causes and Implications

“…The direction of the summer prevailing wind is known to be SSE-SE, which leads to northward coastal currents. Meanwhile, the direction of the winter prevailing wind is NW-NE and generates southward alongshore currents [27].…”

Decadal link between longitudinal morphological changes in branching channels of Yangtze estuary and movement of the offshore depo‐center

“…Given the supply of abundant sediment from adjacent coastal areas and submerged delta (including the continental shelf), the Yangtze estuary experiences alternating net exports and imports of sediment (i.e. erosion and deposition events) under alternating high and low runoff discharges, even though the river sediment load has reduced remarkably (Zhu et al, 2020).…”

“…Over past decades, more than 50000 dams have been constructed and a large number of local engineering projects undertaken in the river basin and its estuary. Surveys have comprehensively examined decadal to seasonal erosion-deposition processes affecting geomorphic units within estuarine and offshore areas of the Yangtze subject to significant variations in water dynamics and sediment supply caused by intense human activities (Liu et al, 2009;Yang et al, 2011;Dai et al, 2013Dai et al, , 2014Dai et al, , 2016Du et al, 2016;Luan et al, 2016;Yang et al, 2016;Zhu et al, 2017;Mei et al, 2018;Zhu et al, 2019;Zhu et al, 2020). It has been established that certain of these morphological changes have led to practical problems, including migration of navigation features (Liu et al, 2009;Dai et al, 2013), increased risk of embankment failure related to water abstraction projects (Ou et al, 2013), and recession of saltmarsh-wetland systems (Wei et al, 2015;Gu et al, 2018).…”