Burningham, H; French, JR; (2009) Seabed mobility in the greater Thames estuary. [Book]. (1st ed.). Crown Estate

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Abstract

This report presents results from a Caird-Crown Estate research project to investigate the geomorphic history of the seabed and associated features within the greater Thames estuary within a region of over 5000km2 bounded by Aldeburgh (Suffolk), Southend-on-Sea (Essex) and Margate (Kent). Bathymetric charts published over the last 180 years have been analysed to assess the geomorphological evolution of the greater Thames seabed. Charts published since the early 1800s comprise sufficient grid reference or ground control detail for georectification onto a common coordinate system (British National Grid), and a total of 10 charts were used here to reconstruct the historical changes in seabed morphology. Systematic errors in the positioning of offshore features proved only problematic for the earliest chart (1824). Soundings were digitised as points from each chart, and the depth measures at each point were converted to Ordnance Datum. The point data were interpolated onto a regular 100 x 100 m grid (3D surface), which formed the basis of further analysis. The historical evolution of the greater Thames seabed was examined using cross- estuary and shore-normal transects; bathymetric change maps and spatial statistics. The analyses illustrated considerable spatial variability in seabed mobility. Within the central Thames, the banks of Barrows, Sunk Sand, Long Sand and Kentish Knock have experienced significant depth changes associated with lateral shifts. In many cases, the bank surface comprises numerous bathymetric highs that appear to migrate along the banks. Progressive changes can be seen at Long Sand Head, which has been prograding northward over the last 180 years, and Kentish Knock, which has been lengthening and changing shape over this period. The Suffolk shoreface has also experienced some gradual shifts in bank position. Cutler bank has moved seaward, whereas Whiting and Aldeburgh Ridge have moved landward. Bawdsey Bank appears to be extending northward, and the Shipwash has shifted around a central axis, with more recent change in shape. It is not clear whether the offshore banks (Gabbards, Galloper) have moved due to systematic positional errors, but the head and tails of these banks do show evidence of growth and decay.

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