1st Edition
Modeling Estuarine Morphodynamics under Combined River and Tidal Forcing UNESCO-IHE PhD Thesis
This research is dedicated to studying longterm estuarine morphodynamic behavior under combined river and tidal forcing. Analysis of river tides in the Yangtze River estuary (YRE) in China, schematized morphodynamic modeling in 1D and 2D mode and morphodynamic modeling of the YRE based on a process-based numerical model (Delft3D) are conducted. Morphodynamic sensitivities to river discharge magnitude and time variations, tidal strength and tidal constituents are then systematically explored.
Analysis of river tides in the YRE reveals strong river-tide interactions and non-linear modulation of tides by river discharge. River discharge alters tidal asymmetries and resultant tidal residual sediment transport.
Analysis of morphodynamic modeling results exposes significant mechanisms inducing tidal residual sediment transport and controlling long-term morphodynamic development. Morphodynamic equilibria in 1D and 2D simulations can be defined by vanishing gradients of tidal residual sediment transports and meeting empirical morphodynamic relationships.
This research indicates the value of numerical modeling in examining long-term morphodynamic development in millennia time scale. Understanding of the controls on morphodynamic behavior in estuaries under river and tidal forcing is to the benefit of managing estuaries’ functions in a long-term point of view.
Abstract
1. Introduction
1.1. Definition and classification of estuaries
1.2. Driving forcing and morphodynamics
1.2.1. River flow and tides
1.2.2. Estuarine morphodynamics
1.3. Morphodynamic modeling
1.4. Objectives and research questions
1.5. Thesis organization
2. Inspiration from the Yangtze River estuary
2.1. Introduction
2.2. Driving forces
2.2.1 River discharge
2.2.2. Sediment discharge
2.2.3. Tides
2.2.4. Estuarine circulations
2.3. Sediment transport dynamics
2.4. Morphodynamics
2.4.1. Millennial geomorphological evolution
2.4.2. Centennial morphodynamic evolution
2.5. Concluding remarks
3. River tidal dynamics
3.1. Introduction
3.2. Setting, data and methods
3.2.1. Introduction to the Yangtze River estuary
3.2.2. Data source
3.2.3. Tidal analysis methods
3.2.4. Numerical model setup
3.3. Data analysis results
3.3.1. Subtidal variations
3.3.2. Time-frequency spectra of tidal species
3.3.3. Time-frequency spectra of tidal constituents
3.3.4. Time-frequency structure of tidal currents
3.3.5. Numerical model results
3.4. Discussion
3.4.1. Non-linear tidal interactions
3.4.2. River-tide interferences
3.4.3. How important is friction to tidal dynamics?
3.4.4. Implications of river tidal dynamics
3.4.5. Thoughts about river tide analysis
3.5. Conclusions
Appendix A. Harmonic analysis results
4. Role of tides
4.1. Introduction
4.2. Model setup
4.3. Model results
4.3.1. Morphodynamic development
4.3.2. Tidal hydrodynamics
4.3.3. Modeled TRST
4.3.4. Analytical TRST
4.4. Discussion
4.4.1. TRST by multiple tidal asymmetries
4.4.2. Impact of river flow on TRST
4.4.3. Rethinking the concept of representative tides
4.4.4. Feedback to reality
4.5. Conclusions
5. Role of river discharge magnitude
5.1. Introduction
5.1.1. Tidal hydrodynamics and sediment transport
5.1.2. Modeling efforts on estuarine morphodynamics
5.1.3. Aim and methodology
5.2. Model setup
5.3. Model results
5.3.1. Hydrodynamics of the schematized model
5.3.2. Morphodynamics of the schematized model
5.3.3. Tidal residual sediment transport
5.3.4. Mechanism analysis
5.4. Discussion
5.4.1. Impact of basin geometry
5.4.2. Role of river discharge
5.4.3. Morphodynamic equilibrium
5.4.4. Shape of equilibrium profiles
5.5. Conclusions
6. Impact of river discharge seasonality
6.1. Introduction
6.2. Model setup
6.2.1. Model schematization
6.2.2. Sensitivity scenarios
6.3. Model results
6.3.1. Sediment transport and fluxes
6.3.2. Morphodynamic sensitivity of hydrograph schematization
6.3.3. Morphodynamic sensitivity of hydrographs
6.4. Discussion
6.4.1. River-tide interactions
6.4.2. Hydrograph schematization
6.4.3. Morphodynamics by seasonally varying river discharges
6.4.4. Impact of extreme floods
6.4.5. Thought about MF approach
6.5. Conclusions
7. Fluvio-deltaic morphodynamics
7.1. Introduction
7.2. Model descriptions
7.3. Model results
7.3.1. Morphodynamics
7.3.1.1. Morphodynamic sensitivity to river discharge
7.3.1.2. Morphodynamic sensitivity to tides
7.3.1.3. Hypsometry
7.3.1.4. Flat areas and channel volumes
7.3.2. Tidal hydrodynamics
7.3.3. Residual currents and residual sediment transport
7.3.4. Sediment budget
7.4. Discussion
7.4.1. Channel-shoal patterns
7.4.2. Impact of river discharge 0n 2D morphodynamics
7.4.3. Impact of tides on 2D morphodynamics
7.4.4. Morphodynamic equilibrium in a fluvio-deltaic system
7.4.5. Transition between river and tide dominance
7.5. Conclusions
8. Modeling the Yangtze River estuary
8.1. Introduction
8.2. Model setup
8.2.1. One-dimensional model setup
8.2.2. Two-dimensional model setup
8.2.3. Model calibration
8.3. Model results
8.3.1. One-dimensional modeling of the South Branch
8.3.2. Two-dimensional modeling of the South Branch
8.3.3. Two-dimensional modeling of the entire estuary
8.4. Discussion
8.4.1. Impact of river and tides
8.4.2. Channel patterns in river-influenced estuaries
8.4.3. Morphodynamic time scales and equilibrium
8.5. Concluding remarks
9. Conclusions and reccomendations
9.1. Concluding remarks
9.1.1. Introduction
9.1.2. Answering the research questions
9.1.3. Overall conclusions
9.1.4. Implications for the YRE
9.2. Recommendations
References
Acknowledgements
Exposure
About the author
Biography
Leicheng Guo
