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You searched for subject:(Loire river estuary). Showing records 1 – 2 of 2 total matches.

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Delft University of Technology

1. de Goede, Roel (author). Regime shift in sediment concentrations in the Loire estuary.

Degree: 2020, Delft University of Technology

A study of five European estuaries by Winterwerp and Wang (2013) showed that tidal ranges increased significantly along with the ongoing narrowing and deepening of these estuaries. In addition to an increase in tidal range, a dramatic increase in suspended sediment concentrations has been observed in the Ems (Germany) and Loire (France) estuaries, often referred to as a regime shift towards hyperturbid state. While it is generally accepted that the increase in tidal range is a consequence of deepening and narrowing, it is not generally true that deepening and narrowing leads to a dramatic increase in sediment concentrations. Whether deepening is a potential cause for the high sediment concentrations observed in the Loire, is still unclear. Although very little observations have been reported over the 20th century, literature clearly shows that sediment concentrations increased drastically over the years. The scarcity of data not only applied for the sediment concentrations over the years but also for bathymetry and hydrodynamics, resulting in uncertainty about the historical states of the estuary. To cope with the large range of uncertainty and variability in the reported observations and model parameters, an idealised model called iFlow has been used. The strength of the iFlow model for this research was twofold. Firstly, iFlow allowed to identify the essential physical processes driving the estuarine sediment dynamics. Secondly, iFlow is computationally efficient, allowing to perform extensive sensitivity studies. In this way, we could determine which processes play a role in the current state of the Loire estuary and how they are affected by deepening. Furthermore, by mapping the effects of the uncertainty on the different physical processes, robust conclusions could be drawn about the effects of deepening despite the given uncertainty. The effects of deepening on the physical processes has been assessed by only varying the depth in the model. Deepening generally resulted in enhanced sediment import or decreased sediment export. Hence, the transport capacity in the Loire became much more favourable for the import of sediment. In order to determine the robustness of these findings, an extensive sensitivity study was performed of 14.157 simulations (1287 conditions for 11 bottom profiles over time) to capture the influence of uncertainties in multiple input parameters. For the bottom profile representing the bathymetry in the year 1900, none of the conditions resulted in a hyperturbid state, whereas independent of the conditions, the likelihood to find a hyperturbid state always increased for increasing depth. From this we can conclude, that the observed regime shift towards high sediment concentrations would not have happened without the deepening of the Loire estuary. Advisors/Committee Members: Dijkstra, Yoeri (graduation committee), Wang, Zhengbing (mentor), van Prooijen, Bram (graduation committee), Delft University of Technology (degree granting institution).

Subjects/Keywords: Loire river-estuary; Hyperturbidity; Idealized modelling; iFlow; Sediment dynamics; Sensitivity Analysis; Proces Based modelling

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

de Goede, R. (. (2020). Regime shift in sediment concentrations in the Loire estuary. (Masters Thesis). Delft University of Technology. Retrieved from http://resolver.tudelft.nl/uuid:4d71a8e1-08e9-4663-a7b4-ae514fa59419

Chicago Manual of Style (16th Edition):

de Goede, Roel (author). “Regime shift in sediment concentrations in the Loire estuary.” 2020. Masters Thesis, Delft University of Technology. Accessed November 28, 2020. http://resolver.tudelft.nl/uuid:4d71a8e1-08e9-4663-a7b4-ae514fa59419.

MLA Handbook (7th Edition):

de Goede, Roel (author). “Regime shift in sediment concentrations in the Loire estuary.” 2020. Web. 28 Nov 2020.

Vancouver:

de Goede R(. Regime shift in sediment concentrations in the Loire estuary. [Internet] [Masters thesis]. Delft University of Technology; 2020. [cited 2020 Nov 28]. Available from: http://resolver.tudelft.nl/uuid:4d71a8e1-08e9-4663-a7b4-ae514fa59419.

Council of Science Editors:

de Goede R(. Regime shift in sediment concentrations in the Loire estuary. [Masters Thesis]. Delft University of Technology; 2020. Available from: http://resolver.tudelft.nl/uuid:4d71a8e1-08e9-4663-a7b4-ae514fa59419


Delft University of Technology

2. Kosters, Anna (author). Human interventions in river-estuary systems: A case study of the Loire, France.

Degree: 2019, Delft University of Technology

Like many rivers around the world, the Loire river in France has a history of human interventions in order to facilitate navigation and port development. Next to affecting bed levels directly, the heavy modification of the river-estuary has induced significant changes in the hydrodynamic and morphodynamic behaviour of the Loire. As a result, the Loire river is experiencing an ongoing bed degradation. In the estuary, the interventions have led to an amplification of the tidal amplitude, a shift of the tidal and salt intrusion limit in upstream direction and a larger tidal asymmetry. According to Winterwerp and Wang (2013), this tidal deformation leads to an increased import of fine sediment in the estuary and a reduced hydraulic drag. This in turn enhances tidal deformation further. Due to this positive feedback mechanism the Loire estuary has evolved into a hyper-turbid state, associated with large suspended sediment concentrations and the formation of fluid mud. The behaviour of the river-estuary on large temporal and spatial scales and its response to historical and possible future interventions is not yet sufficiently understood. Therefore, an idealized, computationally efficient, three-dimensional morphodynamic model of the river-estuary is developed with the FLOW module of the Delft3D software suite, in which the main processes influencing the morphology of the Loire river-estuary are included. The current estuarine geometry, lacking the presence of large intertidal areas, induces a flood-dominant tidal signal. In the mouth of the estuary, the baroclinic pressure gradient introduces a mean landward-directed velocity near the bed and amplifies the mean seaward-directed velocity near the surface. This gravitational circulation causes the formation of an Estuarine Turbidity Maximum at the tip of the salt wedge, which is strengthened further by the flood-dominance of the tide. Model results confirm the feedback mechanism between tidal deformation, the import of fine sediment and the effective hydraulic drag as described above. However, next to tidal deformation, strengthening of the gravitational circulation also plays a large role in this mechanism for the Loire. To mitigate bed degradation, several measures are simulated that decrease the transport capacity of the flow, increase the sediment supply or do both. Over the first 10 years, sediment nourishments are the most effective according to the model. However, after 100 years of simulation the removal of all groynes present within the domain leads to the most sedimentation relative to the reference scenario. To decrease the import of mud into the estuary, two measures have been investigated. Increasing bed levels in the main channel of the estuary mainly leads to a decrease of the tidal range, whereas restoring tidal flats turns the tide from flood- into ebb-dominant. In both cases, a decrease of the salt intrusion length and a significant weakening of the gravitational circulation occurs, leading to a tidally averaged export of fine… Advisors/Committee Members: Wang, Zheng Bing (graduation committee), Mosselman, Erik (mentor), van Maren, Bas (graduation committee), Delft University of Technology (degree granting institution).

Subjects/Keywords: Loire river-estuary; Idealized modelling; Delft3D; Morphodynamics; Bed degradation; Hyper-turbidity; Estuarine turbidity maximum

Record DetailsSimilar RecordsGoogle PlusoneFacebookTwitterCiteULikeMendeleyreddit

APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Kosters, A. (. (2019). Human interventions in river-estuary systems: A case study of the Loire, France. (Masters Thesis). Delft University of Technology. Retrieved from http://resolver.tudelft.nl/uuid:b4ddbed0-5ba6-4071-b7ab-931aae8b6912

Chicago Manual of Style (16th Edition):

Kosters, Anna (author). “Human interventions in river-estuary systems: A case study of the Loire, France.” 2019. Masters Thesis, Delft University of Technology. Accessed November 28, 2020. http://resolver.tudelft.nl/uuid:b4ddbed0-5ba6-4071-b7ab-931aae8b6912.

MLA Handbook (7th Edition):

Kosters, Anna (author). “Human interventions in river-estuary systems: A case study of the Loire, France.” 2019. Web. 28 Nov 2020.

Vancouver:

Kosters A(. Human interventions in river-estuary systems: A case study of the Loire, France. [Internet] [Masters thesis]. Delft University of Technology; 2019. [cited 2020 Nov 28]. Available from: http://resolver.tudelft.nl/uuid:b4ddbed0-5ba6-4071-b7ab-931aae8b6912.

Council of Science Editors:

Kosters A(. Human interventions in river-estuary systems: A case study of the Loire, France. [Masters Thesis]. Delft University of Technology; 2019. Available from: http://resolver.tudelft.nl/uuid:b4ddbed0-5ba6-4071-b7ab-931aae8b6912

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