Hydrodynamics and morphodynamics of shallow tidal channels and intertidal flats

Abstract

In this thesis, mechanisms which control morphodynamics of shallow tidal embayments are investigated analytically. In the process of exploring these mechanisms (specifically asymmetries in bottom stress, τ), basis momentum and mass balances which govern flow in these systems are clarified. Temporal asymmetries in τ are investigated via a new perturbation scheme which quantifies nonlinear processes and combines geometric controls on asymmetry into a single non-dimensional parameter. Implications of spatial asymmetries in τ are investigated though stability criteria based on a uniform distribution of τ. Morphologic observations of both tidal channels and intertidal flats are consistent with a unifonn distribution of τ at equilibrium. Investigation of morphodynamic mechanisms leads to scalings of momentum and continuity which diverge from classical models. Scalings for prismatic channels with strong tidal asymmetries indicate friction often dominates acceleration in the momentum equation. The resulting "zero-inertia" balance gives a time-varing diffusion equation which requires along-channel amplitude to decay. Uniform τ justifies a new scaling of continuity for exponentially-shaped channels. In such channels, along-channel gradients in tidal velocity are small and are often dominated by gradients in cross-sectional area. The resulting first-order wave equation allows only constant amplitude, forward propagating waveforms which are independent of channel length.