The migration of large scale bed forms in the Dee Estuary

Way, Oliver (2013) The migration of large scale bed forms in the Dee Estuary. PhD thesis, Prifysgol Bangor University.

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The Dee Estuary, located on the southern side of Liverpool Bay, in the Eastern Irish Sea, is macrotidal with a peak spring tidal range in excess of 10m. The large tidal range and associated strong currents make the estuary a very dynamic system with large fluxes of sediment. River canalisation and land reclamation between 1700 and early 1900 has significantly altered the hydrodynamic and sedimentological conditions. This caused the main navigation channel to migrate from the eastern side to the western shore of the estuary. Large bed forms are visible in the intertidal zones of the mouth of the estuary in aerial photographs. These features can be seen to be migrating into the estuary from X-band radar images. Dune migration can lead to residual sand transport rates, depending of the direction and magnitude of the dune characteristics. It is therefore important to monitor the movement of these large scale bed forms to determine the stability of the complex area of sand banks and channels in the Dee Estuary. Understanding the patterns of dune migration and associated sediment transport is fundamental for effective sediment management of an estuary, as well as an important consideration for offshore construction. Monitoring the migration patterns of large scale bed forms in the mouth of the Dee Estuary will show if they correlate with the transport of sediment into the estuary and how much they contribute to the sediment budget of the estuary. The driving forces behind large scale bed form migration are investigated to determine whether it is the action of waves, tidal currents or a combination of the two which are important. ADCP deployments on West Kirby Sands show a strong flood dominant tide which could be indicative of a flood dominant residual sediment transport. A 'three pronged' approach is taken to understand the migration of large scale bed forms in the mouth of the Dee Estuary. This includes remote sensing with X-band radar data, field measurements using DGPS surveying and numerical modelling techniques. Modelling of the estuary using TELEMAC, validated with ADCP measurements at West Kirby Sands, shows flood dominant sediment transport over a tidal cycle. A 'model chaining' approach is taken to simulate tides, waves, wave generated currents and sediment transport. Developments are made to include a variable bed roughness feedback method into TELEMAC.

Item Type: Thesis (PhD)
Subjects: Degree Thesis
Departments: Degree Thesis
College of Natural Sciences > School of Ocean Sciences
Date Deposited: 14 May 2015 05:22
Last Modified: 05 Apr 2016 15:40
URI: http://e.bangor.ac.uk/id/eprint/4541
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