Author(s): Haoyan Dong; Henk Schuttelaars; Tom De Mulder

Linked Author(s):

Keywords: Overtide; Residual dynamics; Wetting and drying algorithm; One-dimensional hydrodynamic model; Delaware estuary

Abstract: Nonlinear tidal processes in water motion, which generate overtides and residual dynamics, are crucial not only for the morphodynamic evolution of tidal systems, but also for the transport of contaminants, nutrients and biogeochemical tracers. Traditional approaches, such as that of Parker (1991), explain these nonlinear processes using perturbation methods that assume a small tidal amplitude-to-depth ratio. While these methods effectively detect nonlinear mechanisms, quantifying their relative importance in practical applications remains challenging. Moreover, this assumption limits their applicability in very shallow and intertidal areas, where it is violated. To address this limitation, we propose a new methodology to assess the relative importance of overtide generation mechanisms. This approach is based on the fully nonlinear shallow water equations, combined with Defina’s (2000) wetting and drying approach to account for subgrid-scale topography. As a first validation step of this methodology, we applied it to a schematization of the Delaware estuary, the same case studied by Parker (1991), where very shallow or intertidal areas are absent. This setup allows for a direct comparison, particularly for the cases where an M2 tidal constituent was imposed at the seaward boundary. Our analysis confirms the dominant role of the nonlinear continuity term in the M4 overtide generation, while the combined velocity and sea surface elevation nonlinearity in bed friction plays a secondary role. For the M6 overtide, the quadratic velocity friction term, which accounts only for velocity nonlinearity, plays a pivotal role. Additionally, the combined velocity and sea surface elevation nonlinearity in bed friction is the main driver of mean sea level generation. The inclusion of mean Delaware River runoff enhances the M4 generation while slightly reducing the amplitudes of the M6 tidal constituent, and it leads to an increase in mean sea surface elevation. The observations above are consistent with Parker's results. In future research, the new methodology will be further explored for tidal systems with extensive intertidal areas, where Parker’s approach is no longer applicable.

DOI: https://doi.org/10.64697/978-90-835589-7-4_41WC-P1666-cd

Year: 2025