Investigations on the morphodynamics of sandy tidal flats: a modeling application

Abstract

Modeling of morphodynamic behavior and evolution of sandy tidal flats commonly comprises the utilization of a sequence of techniques to characterize and/or quantify the interaction between various hydrodynamic forcing factors and the geomorphologic response of the receiving environment. An alternative for establishing the geomorphological behavior of sandy tidal flats could be introduced in the context of coastal classification of morphodynamic regime. This contribution investigates tidal flat morphodynamics in the context of generic coastal classifications and aims at a medium to long-term characterization of its evolution, by presenting the methodology and results of a series of investigations conducted on sandy tidal flats in Northern Ireland. The active inter-tidal sandy tidal flats of Newtownards vary between 1200 and 500 m wide and can be characterized by a relative tidal range (RTR) factor of 2.3–7. This situates the inter-tidal zones in the mixed waves and tide domain. The sensitivity of sediment redistribution to combined water level/wave height makes wave energy dissipation due to bottom friction the primary shoaling process during relative high-energy events. Tidal currents, a constant feature on the ultra dissipative environments, are also most acute when combined wave/tide currents are present. Thresholds of sediment entrainment are exceeded and resuspension initiated when water levels approach 1.0 m OD and significant wave height are at a maxima of 1.5 m. These modeling results when taken into an empirical situation by deployment of instruments illustrated that the relationship between waves and water levels in these environments is very dependent on wave penetration in the water column. Morphodynamic characterization of tidal flats could allow for further understanding on their long-term behavior if modeling is utilized to reproduce morphodynamic scenarios, which help identify wave/water level relationships on fine sands.