Net suspended sediment transport modulated by multiple flood-ebb asymmetries in the progressive tidal wave dominated and partially stratified Changjiang Estuary

• Published in: Marine geology 2022-01, Vol.443, p.106702, Article 106702
• Main Authors: Li, Zhanhai, Jia, Jianjun, Wang, Ya Ping, Zhang, Guoan
• Format: Article
• Language: English
• Subjects: Changjiang Estuary; Compensation flow of Stokes drift; Flood-ebb asymmetry; Net sediment transport; Progressive tidal wave; Sediment supply limitation
• ISSN: 0025-3227; 1872-6151
• DOI: 10.1016/j.margeo.2021.106702

In many estuaries, current velocity, suspended sediment concentration (SSC), and water depth have notable flood-ebb asymmetries in magnitude or duration. Such asymmetries can make marked impact on estuarine sediment transport and require in-depth analysis of the underlying mechanism. Based on field measurement over a neap-spring cycle in the Changjiang Estuary in January 2015, net suspended sediment transport modulated by multiple asymmetries were analyzed. The results showed that there were notable flood-ebb asymmetries in the current velocity, current duration, SSC, and water depth. The former two were ebb-dominated, while the latter two were flood-dominated. The net suspended sediment transport was landward and exhibited remarkable tidal fluctuation in magnitude. Ebb-dominated velocity and duration asymmetries favored seaward transport, but flood-dominated SSC and water depth asymmetries promoted landward transport. The relative contribution of these asymmetries to the net sediment transport was different and closely related to their asymmetry intensities. The magnitude of net sediment transport was highly modulated by the combined effects of these asymmetries. Further analyses revealed that the ebb-dominated asymmetries in velocity and duration were controlled by river flow, tidal wave deformation, and compensation flow of Stokes drift. The flood-dominated water depth asymmetry was related to the progressive tidal wave. The flood-dominated SSC asymmetry was mainly attributed to the lower SSCs in early ebbs, notable sediment supply limitation in late ebbs, wind wave height asymmetry, and gravitational circulation. Additionally, it is worth noting that the progressive tidal wave can yield strong current asymmetry, notable water depth asymmetry, and obvious wind wave height asymmetry during strong wind periods. •Multiple important flood-ebb asymmetries coexist in a tidal cycle in natural estuaries.•Net sediment transports are highly modulated by the combination of multiple asymmetries.•Flood- and ebb-dominated asymmetries play opposite roles in net sediment transport.•Compensation flow of Stokes drift has important influence on current asymmetry.•Variation in sediment availability for resuspension can yield notable SSC asymmetry.