Modeling Estuarine Morphodynamics under Combined River and Tidal Forcing : UNESCO-IHE PhD Thesis

This book examines rive tidal dynamics and associated morphodynamics under combined river and tidal forcing. Non-stationary tidal analysis by two methods, i.e. harmonic analysis and continuous wavelet transformation, is conducted on the data in the Yangtze River estuary. Data analysis reveals strong river tidal interactions and non-linear modulation of tides by river discharge. Analysis of long-term morphodynamic modeling results suggests three important mechanisms driving residual sediment transport, namely river flow, river-tide interaction and tidal asymmetry. The morphodynamic equilibrium is approached in long-term by reducing gradients of residual sediment transport and empirical relationships.

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.