An Idealized Model and Systematic Process Study of Oxygen Depletion in Highly Turbid Estuaries

Talke, Stefan A.; Swart, H.E. de; Jonge, Victor N. de

doi:10.1007/s12237-009-9171-y

Cited by 86 publications

(73 citation statements)

References 30 publications

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“…The ETM has moved upstream, but the physical mechanism producing this change is still debated. Talke et al (2009a) show that observed changes can be reproduced with a simple model of gravitational circulation and river discharge; however, other studies speculate that tidal pumping and tidal asymmetry are important (Wurpts and Torn 2005).…”

Section: Introductionmentioning

confidence: 89%

“…Here, < s(x) > is the observed along-channel timeand depth-averaged salinity profile which describes the gradual decrease of the salinity from the sea to the river (i.e., the model is diagnostic in salinity). The salinity profile is prescribed as a hyperbolic tangent profile along the estuary that depends on the freshwater discharge (see Talke et al 2009a).…”

Section: Model Formulationmentioning

confidence: 99%

“…The Ems estuary is exponentially converging with a convergence length L b of 30 km. The system is partially mixed and the landward limit of the salt intrusion varies with the river discharge and is usually found between 20 and 30 km (Talke et al 2009a).…”

Section: Characteristics Of the Ems Estuarymentioning

confidence: 99%

“…This trapping of sediment is the result of the complex interaction of the water motion (forced by tides, river discharge, density gradients) and sediment dynamics (availability of sediment, sediment size, flocculation). At the locations with high sediment concentrations, depleted levels of oxygen (and hence degraded environmental conditions) are often observed (De Jonge 1983;Talke et al 2009a). Since anthropogenic and natural changes (e.g., sea-level rise, land subsidence, etc.)…”

Section: Introductionmentioning

confidence: 99%

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The effect of tidal asymmetry and temporal settling lag on sediment trapping in tidal estuaries

2010

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Over decades and centuries, the mean depth of estuaries changes due to sea-level rise, land subsidence, infilling, and dredging projects. These processes produce changes in relative roughness (friction) and mixing, resulting in fundamental changes in the characteristics of the horizontal (velocity) and vertical tides (sea surface elevation) and the dynamics of sediment trapping. To investigate such changes, a 2DV model is developed. The model equations consist of the widthaveraged shallow water equations and a sediment balance equation. Together with the condition of morphodynamic equilibrium, these equations are solved analytically by making a regular expansion of the various physical variables in a small parameter. Using these analytic solutions, we are able to gain insight into the fundamental physical processes resulting in sediment trapping in an estuary by studying various forcings separately. As a case study, we consider the Ems estuary. Between 1980 and 2005, successive deepening of the Ems estuary has significantly altered the tidal and sediment dynamics. The tidal range and the surface sediment concentration has increased and the position of the turbidity zone has shifted into the freshwater zone. The model is used to determine the causes of these historical changes. It is found that the increase of the tidal amplitude toward the end of the embayment is the combined effect of the deepening of the estuary and a 37% and 50% reduction in the vertical eddy viscosity and stress parameter, respectively. The physical mechanism resulting in the trapping of sediment, the number of trapping regions, and their sensitivity to grain size are explained by careful analysis of the various contributions of the residual sediment transport. It is found that sediment is trapped in the estuary by a delicate balance between the M 2 transport and the residual transport for fine sediment (w s = 0.2 mm s −1 ) and the residual, M 2 and M 4 transports for coarser sediment (w s = 2 mm s −1 ). The upstream movement of the estuarine turbidity maximum into the freshwater zone in 2005 is mainly the result of changes in tidal asymmetry. Moreover, the difference between the sediment distribution for different grain sizes in the same year can be attributed to changes in the temporal settling lag.

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Section: Introductionmentioning

confidence: 89%

Section: Model Formulationmentioning

confidence: 99%

Section: Characteristics Of the Ems Estuarymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The effect of tidal asymmetry and temporal settling lag on sediment trapping in tidal estuaries

2010

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“…Also, turbid waters usually have low oxygen concentrations because organic material in the sediment consumes oxygen. This can lead to hypoxic zones (cf Uncles et al 1998;Garnier et al 2001;Talke et al 2009). …”

Section: Introductionmentioning

confidence: 99%

Effect of bottom stress formulation on modelled flow and turbidity maxima in cross-sections of tide-dominated estuaries

2009

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A three-dimensional numerical model with a prognostic salinity field is used to investigate the effect of a partial slip bottom boundary condition on lateral flow and sediment distribution in a transect of a tidally dominated channel. The transect has a symmetrical Gaussian cross-channel bottom profile. For a deep, well-mixed, tidally dominated channel, partial slip decreases the relative importance of Coriolis deflection on the generation of cross-channel flow patterns. This has profound implications for the lateral distribution of residual salinity that drives the cross-channel residual circulation pattern. Transverse sediment transport, however, is always found to be governed by a balance between advection of residual sediment concentration by residual lateral flow on the one hand and cross-channel diffusion on the other hand. Hence, the changes in the cross-channel distribution of residual salinity modify the lateral sediment distribution. For no slip, a single turbidity maximum occurs. In contrast, partial slip gives a gradual transition to a symmetrical density distribution with a turbidity maximum near each bank. For a more shallow, partially mixed tidal channel that represents the James River, a single turbidity maximum at the left bank is found irrespective of the near-bed slip condition. In this case, semi-diurnal contributions to sediment distribution and lateral flow play an important role in cross-channel sediment transport. As vertical viscosity and diffusivity are increased, a second maximum at the right bank again exists for partial slip.

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Structure of the turbidity field in the Guadalquivir estuary: Analysis of observations and a box model approach

et al. 2014

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A study is presented on the transport of suspended particulate matter (SPM) in the Guadalquivir estuary during low river flow conditions. Observations show that tidally induced SPM exceeds that associated with catchment-derived inputs. The main mechanisms that contribute to longitudinal transport are identified and quantified by analyzing the tidally averaged and depthintegrated SPM flux decomposition over time and space. The net transport is generally directed upstream, although differences in the direction between spring and neap tides are identified. The transport is largely controlled by the mean advection, the tidal pumping associated with the covariance between SPM concentration and current, and the tidal Stokes transport. The convergence of the transport associated to these mechanisms alone explains the presence of primary and secondary estuarine turbidity maxima. The tidal reflection at the upstream dam appears to play a significant role in their generation, as evidenced by the convergence zones of the M4 and M2 induced tidal pumping transports. The spatial structure of the transport motivates the development of a box model that describes the concentration of SPM and its exchange between different stretches along the estuary at subtidal time scales. The model is fed by the net SPM transport obtained from observations. Analysis of the morphodynamical state of the estuary using the box model indicates that erosion is dominant in the stretches close to the estuary mouth and that this sediment is transported upstream and deposited in the middle part of the estuary. This process is more influential during spring tides than during neap tides.

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An Idealized Model and Systematic Process Study of Oxygen Depletion in Highly Turbid Estuaries

Cited by 86 publications

References 30 publications

The effect of tidal asymmetry and temporal settling lag on sediment trapping in tidal estuaries

The effect of tidal asymmetry and temporal settling lag on sediment trapping in tidal estuaries

Effect of bottom stress formulation on modelled flow and turbidity maxima in cross-sections of tide-dominated estuaries

Structure of the turbidity field in the Guadalquivir estuary: Analysis of observations and a box model approach

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