183. Along the East Anglian coastline, longshore transport is generally to the south, although localised departures from this trend are apparent at the mouths of estuaries (Royal Haskoning 2010). Seaward of approximately the 20m isobath, even large wave heights or long wave periods have a very limited influence on the sea bed processes.
184. The coasts to the north and south of the landfall location for the proposed East Anglia THREE project are generally eroding and this erosion is likely to increase in the future with sea-level rise.
185. The shoreline management policy over the lifetime of the proposed East Anglia THREE project at East Lane, Bawdsey and to the south of the Deben Estuary is to “Hold the line of existing defences” (Royal Haskoning 2010). This is likely to lead to erosion of the foreshore seaward of the defence structures, with foreshore steepening and a loss of beach material.
186. At Bawdsey cliffs, where the offshore cable corridor landfall is located, the shoreline management policy is “No Active Intervention” (Royal Haskoning, 2010). As the shingle beach becomes depleted, it is likely to lead to erosion of the backing cliffs. These cliffs are currently relatively stable with only occasional slumping, which can occur during notable storm events.
187. A highly conservative upper bound of retreat of the Bawdsey cliffs over the 25 year operational lifetime of the proposed East Anglia THREE project is 100m, at an average rate of 4m per year (ABPmer 2013). A similarly conservative estimate of the changes in the intertidal and sub-tidal exposures of London Clay at Bawdsey is lowering of the shore platform by up to 0.75m during the 25 year operational lifetime of the proposed East Anglia THREE project (ABPmer 2013). It is recognised that measureable change in the cliff position and foreshore level occurred during the winter storms of December 2013, but these events were exceptional in their magnitude and frequency of occurrence. The values presented as the conservative upper bound of cliff retreat and shore platform lowering are based on longer term average rates of change that take into consideration periods of relative stability and more notable changes associated with individual storm events. Therefore these values remain representative of the longer term rates of change at the landfall over the operational lifetime of the proposed East Anglia THREE project.
7.6 Potential Impacts
188. The principal receptors with respect to the topic of marine geology, oceanography and physical processes are those features with an inherent geological or
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm Chapter 7 Marine Geology, Oceanography and Physical Processes Page 38
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