Modelling of Cohesive Sediment Transportation, Deposition and Resuspension in the Haringvliet Mouth.

Abstract

In the Dutch coastal zone, where the marine environment is characterized by shallow depths and highly energetic hydrodynamic conditions, the cohesive sediments, or mud, play an important role in the local morphology. For instance, mud deposits and high concentrations of suspended particulate matter (SPM) occur frequently, especially during extreme wave conditions, which lead to a great concern to transportation authorities and coastal managers. Several researchers contributed to the understanding of the cohesive sediment dynamics in the Dutch coastal zone. Nevertheless, the mechanism of cohesive sediment transportation, deposition and resuspension, especially due to wave effects, needs further studies and careful formulation. The main objective of this study is to increase the understanding of the complex patterns of cohesive sediments transportation, deposition and resuspension due to wave effects with tide, wind, density-driven flow in the Dutch coastal area. The study focuses on the areas adjacent to the approach channel of the port of Rotterdam and Haringvliet Mouth, which are characterized by complex interactions between hydrodynamics and sedimentation. Based on the scale linkage theory of de Vriend and rules of Roelvink to keep models simple, the study is carried out with three models at different spatial and temporal scale. Firstly, the study starts with the extension of the existing ZUNO model of the North Sea in a macro spatial scale using Delft3D FLOW and WAVE modules. The sediment movements under wave dynamics are verified as well. Secondly, the domain decomposition technology to generate locally refined grid to cover the studied area. Simulations are carried out with flow, wave, sediments, and morphology modules of Delft3D. Thirdly, the simulated results with the ZUNO coarse grid model is utilised as the boundary condition of another fine grid model of the Haringvliet Mouth. This model is set up to study the influence of waves upon the cohesive sediments in the Haringvliet Mouth in a meso-temporal and spatial scale. The specific boundary conditions of the model are introduced intentionally with harmonic tidal forcing and real time discharge from the Haringvliet Sluice. After the calibration of the wave model and cohesive sediment transportation model, the coupled models show the correct pattern of the cohesive sediment distribution in the area. It reproduces successfully the cohesive sediment transportation, deposition and resuspension pattern mainly due to wave effects in the areas adjacent to the approach channel of the port of Rotterdam and Haringvliet Mouth, which has been verified by measured sediments data. The model results show that the wave dynamics is one of the most significant processes behind the sediment movements in the Haringvliet Mouth.