Fluid mud dynamics in a tide-dominated estuary: A case study from the Yangtze River

Wu, Hao; Wang, Ya Ping; Gao, Shu; Xing, Fei; Tang, Jieping; Chen, Dezhi

doi:10.1016/j.csr.2021.104623

Cited by 13 publications

(8 citation statements)

References 33 publications

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“…For ebb tides, stronger stratification was observed during the event period. Previous studies have shown that sediment stratification could suppress turbulence and reduce the bottom drag (Adams and Weatherly, 1981;Tu et al, 2019;Wu et al, 2022). However, when comparing data from before and after the event, estimations C D were generally the same during ebb tides (Figure 10).…”

Section: Variation Of C D During An S2 Winter Eventmentioning

confidence: 76%

Bottom Drag Variations Under Waves and Currents: A Case Study on a Muddy Deposit off the Shandong Peninsula

Liu

2022

Front. Earth Sci.

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Bottom drag coefficient is one of the key parameters in quantifying shelf hydrodynamics and sediment transport processes. It varies markedly due to dynamic forcing and bed type differences, so a set of empirical values have been used for beds of coarse material where bedforms are often present. In comparison, dramatically fewer such rule-of-thumb values are available for muddy beds. Here, we present results of variations in bottom drag as calculated from in situ measurements by bottom-mounted tripods that were placed across the top of a muddy deposit during two different deployments, one in summer and another in winter. A tidal asymmetry of bottom drag was observed, most likely caused by variations of local bed roughness. For hydrodynamically smooth (Re<2.3×105) flows, computed values of bottom drag coefficient were fairly scattered but still showed an overall decreasing trend with an increase in Reynolds number. The bottom drag coefficient for hydrodynamically rough or transitional flow was typically constant, while the averaged drag coefficient over all observation periods was 1.7×10−3. Smaller waves (bottom orbital velocity ub <0.1 m/s) had a very limited impact on the bottom drag coefficient. However, with an increase in ub, the wave–current interactions can decrease the time-averaged near-bed velocity and enhance turbulent kinetic energy, thus leading to an increase in the drag coefficient.

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Section: Variation Of C D During An S2 Winter Eventmentioning

confidence: 76%

Bottom Drag Variations Under Waves and Currents: A Case Study on a Muddy Deposit off the Shandong Peninsula

Liu

2022

Front. Earth Sci.

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“…In order to obtain field SSCs, the method described in Wu et al (2022) was adopted to calibrate OBS turbidity versus SSC; and the OBS turbidities were converted to SSCs based on the regression curves (Figure 4). ABS calibration was conducted with the recursive algorithmic method: the sediment sound-absorption coefficient was acquired by referring to SSCs from OBS, and ABS SSC profiles were then obtained by recursive algorithmic (see details in Wu et al (2022). The grain size distributions of bed sediment and field water samples were obtained with a laser diffraction particle size analyzer (range 0.02-2000 mm, Malvern MasterSizer 2000).…”

Section: Ssc Calibration and Grain Sizementioning

confidence: 99%

“…Given its importance, there have been a few numerical efforts to incorporate consolidation in the simulation of fluid mud (e.g., Winterwerp, 1999). Moreover, in estuaries and coastal oceans, strong tidal currents have the ability to erode and entrain fluid mud into the upper water column (Becker et al, 2018;Wu et al, 2022).…”

Section: Introductionmentioning

confidence: 99%

“…Suspended sediment in the water column gradually settles to form fluid mud during periods of weak hydrodynamics, such as slack water. This phenomenon is more prevalent in estuaries characterized by high SSC, including the Jiaojiang (Li L. et al, 2023), Severn (Manning et al, 2010), Weser (Becker et al, 2013), and Yangtze estuaries (Wu et al, 2022). The flocculation of suspended sediment is crucial for fluid mud formation, as it facilitates the rapid settling of sediment during slack water periods.…”

Section: Introductionmentioning

confidence: 99%

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Fluid mud induced by periodic tidal advection and fine-grained sediment settling in the Yangtze estuary

Wu,

Tang,

et al. 2023

Front. Mar. Sci.

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This study presents in-situ observations of fluid mud in the Yangtze Estuary via a bottom tripod. Six occurrences of periodic fluid muds (F1-F6) were observed at high slack water, with suspended sediment concentration (SSC) exceeding 10 kg/m3. The thickness of the fluid mud varied across the six occurrences, reaching a maximum of 0.32m. Notably, temperature and salinity anomalies were observed within the fluid mud. The formation of fluid mud was found to be influenced by turbulence, with turbulence kinetic energy (TKE) below 5×10-4 m2/s2 favoring settling as the primary cause of formation. The critical shear stress (τcw) for fluid mud formation was estimated to be approximately 0.09 Pa. The formation of fluid muds during early tidal cycles was attributed to liquefaction and bed erosion resulting from strong waves. However, in most cases, the wave energy was insufficient for erosion, suggesting that advection played a role in sediment supply during the subsequent tide cycles. The increased cross-channel current velocity during flood facilitated the lateral transport of a significant amount of eroded sediment from shallow water into the channel. Due to its short duration, the fluid mud layer was entrained by the current before consolidation. Enhanced turbulence led to the breakdown of fluid mud at the early ebb. The critical τcw for fluid mud breakdown depended on the density and duration of the fluid mud, with a maximum value of up to 0.70 Pa. The absence of the fluid mud layer during low slack water and neap tide was associated with a reduction in advection and tidal pumping, disrupting the original sediment balance between supply and demand. These data provide valuable insights into the formation and breakdown of fluid mud, contributing to estuarine hydrodynamic modeling studies and enhancing the understanding of estuary dynamics.

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“…The hindering effects that are observed under quiescent conditions when the concentration exceeds the certain limit (approximately 10 kg/m 3 ) are reduced in highly turbulent conditions (Gratiot et al, 2005). Meanwhile, the bottom water turbulence will be suppressed if the near-bed high SSC prevails and generates a strong vertical stratification, which prevents the upper high tidal energy from being transferred into the water bottom and impacts the erosion and deposition of bed (Shen et al, 2020;Wu et al, 2022).…”

Section: Introductionmentioning

confidence: 99%

Sedimentation of cohesive sediments at the subtidal flat affected by wind wave in high turbidity estuary

Shen

Zhu²,

Lou³

et al. 2023

Front. Mar. Sci.

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Sedimentation is an important mechanism to mitigate the shrinking of tidal flat and to restore its ecological function by means of sand or mud nourishment. To explore the sedimentation of cohesive sediments, a seabed tripod observation system was deployed at the subtidal region of the Hengsha Shoal adjacent to the turbidity maximum zone of the Yangtze Estuary for 11 days. The results showed that the fine sediment with the median grain size around 8 mm occupied the whole water column. The seabed was in relative equilibrium state with the fluctuation of bed level smaller than 16 mm during the moderate wind condition while the seabed experienced a rapid erosion of 38mm and a successive intensive accretion of 68mm during the process of wind wave and swell. The bottom hydrodynamic at 0.3mab during the bed accretion was stronger than that during the bed erosion. The deposition process of cohesive sediments can be better described by the simultaneous deposition paradigm than that by the exclusive deposition paradigm according to the direct data-model comparison of the bed level changes, especially during the impact of fluid mud. Three possible reasons for the better performance of the simultaneous deposition paradigm were proposed. The first possibility is that the fine suspended sediments do maintain a continuous contact with the sediment bed since the direct bed level changes during our observation period has been well reproduced by the simultaneous deposition paradigm. The second possibility is the SSC-induced turbulence damping which facilitates the fine sediment settling in the form of cohesive sediment flocs, indicating the settling of sediments can’t be judged by the critical shear stress for deposition just based on the single particle grain size. The last possibility is the fluid mud-induced overestimated bed shear stress by using turbulent velocity fluctuation above the fluid mud-water interface, which produces excess sediment erosion waiting to be compensated by the simultaneous deposition paradigm. For practical modeling purposes, modeling under the simultaneous deposition paradigm can give satisfactory results for the sedimentation of cohesive sediment especially during the impact of wave or swell.

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Fluid mud dynamics in a tide-dominated estuary: A case study from the Yangtze River

Cited by 13 publications

References 33 publications

Bottom Drag Variations Under Waves and Currents: A Case Study on a Muddy Deposit off the Shandong Peninsula

Bottom Drag Variations Under Waves and Currents: A Case Study on a Muddy Deposit off the Shandong Peninsula

Fluid mud induced by periodic tidal advection and fine-grained sediment settling in the Yangtze estuary

Sedimentation of cohesive sediments at the subtidal flat affected by wind wave in high turbidity estuary

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