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3D hydrodynamic and morphodynamic modelling of offshore sandbanks

Clee, Stephen 2020. 3D hydrodynamic and morphodynamic modelling of offshore sandbanks. PhD Thesis, Cardiff University.
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Abstract

Offshore sandbanks are large sedimentary bodies observed on the bed of tidal seas around the world. They play a number of important roles in coastal environments including coastal protection, sediment sources for dredging, natural habitats and sites for offshore wind farms. Sandbanks are actively dynamic; formed and maintained by intensive currents and the local tidal regime. Understanding their response to hydrodynamic conditions and sediment transport processes is important for coastal management. Numerical modelling is seen as an important tool to study this. Simple numerical models can be easily developed to simulate and predict the response of sandbanks to a variety of physical processes. However, hydrodynamic and sediment transport processes are very complex and oversimplifying numerical models can lead to them becoming unreliable. For example, many numerical models use 2D hydrodynamics therefore neglecting the vertical velocity components - which are known to in uence sediment transport. This research aims to develop an advanced numerical model to study the effect of 3D hydrodynamics and morphodynamics on the offshore sandbanks in the southern North Sea. The model results showed that in general the 2D model simulated lower velocities compared to the 3D model. The difference in the 2D and 3D depth averaged velocities was greatest during peak flows and the spring tidal cycles. The 3D vertical profiles showed that the near bed velocities at these times tended to be larger than the 2D depth averaged velocity. Since sediment transport is influenced more by the near bed currents, this implies that consideration of 2D hydrodynamics may in turn underestimate sediment transport rates and sandbank evolution. Morphodynamic modelling showed that sediment was eroded in the sandbanks troughs and transported towards the crests. With consideration of a simple normal wave condition there was reduced deposition on the crest and some of the shallower crests exhibited areas of erosion. This pattern was not visible without the wave condition and highlights the need to consider all of these factors in tandem.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: Offshore Sandbanks Numerical Modelling TELEMAC 3D Hydrodynamics Morphodynamic Evolution North Sea
Date of First Compliant Deposit: 10 May 2021
Last Modified: 10 May 2021 10:30
URI: http://orca.cardiff.ac.uk/id/eprint/141002

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