Phase
Potential Impact
WCS Details
will be between 0.5 – 3m into the bed. Anchor arrays (of 4 – 6 no. anchors) will typically be smaller than jack-up barge legs
Assessment Method
Assessment of Effect
previously been displaced will avalanche back into the depression until a maximum stable slope angle is achieved. The pits will infill under tidally-driven sediment transport, probably over a timescale of months to years. For anchors, anchor scars will be created in the sea bed. These will become reworked and flattened to a baseline conditions by the action of tidal currents over a few tidal cycles.
Significance of impact on receptors = Not significant
Construction and Decommissioning
Operational
Disruption to coastal morphology at cable landfall.
Changes to the tidal regime due to the presence of the foundation structures.
Horizontal Directional Drilling (HDD) at landfall at Bawdsey.
Array of WTGs founded on GBS
• Conceptual understanding of potential impact
• Numerical modelling using Delft3D- FLOW
• Existing evidence base from other wind farms
• Conceptual understanding of potential impact
• Interpretation against baseline tidal current values (typically 1.15 – 1.25m/s on peak spring tides)
• Operational
Changes to the wave regime due to the presence of the foundation structures.
Array of WTGs founded on GBS
• Numerical modelling using Delft3D- SWAN
• Existing evidence base from other wind farms
• Conceptual understanding of potential impact
• Interpretation against baseline wave climate values (typically Hs = 0.5 – 1.0m and Tm = 3.5 – 4.0s)
• Operational
Changes to the sediment transport regime due to the presence of the foundation structures.
Array of WTGs founded on GBS
• Outputs from numerical modelling using Delft3D FLOW and SWAN
• Standard empirical equations (mobilisation and settling of sediment particles)
• Existing evidence base from other wind farms and industry guidance (Kenyan & Cooper, 2005)
• Conceptual understanding of potential impact
• Interpretation against baseline sediment transport regimes
Operational
Scour effects due to the presence of the foundation structures, resulting in erosion, re-suspension and settling of sediments.
Jackets (no scour protection planned) and GBS (scour protection provided) both considered.
• Outputs from numerical modelling using Delft3D FLOW and SWAN
• Standard empirical equations (empirical scour formulae)
• Existing evidence base from other wind farms
Phys_Proc_background Sept 2013
East Anglia THREE & East Anglia FOUR Page 37
Scour hole development will occur around individual legs of a jacket, and group scour under the jacket may also occur. With scour protection provided, no scour will occur around the GBS.
Significance of impact on receptors = Not significant
Local changes in tidal current and wave regimes may induce scour. The broader bedload and suspended sediment transport regimes will be largely unaffected as chnages in tidal and wave regimes are so minor. Similarly, there will be no change in the sediment transport regime at the shore.
Significance of impact on receptors = Not significant
Maximum reductions in wave height appear within, or along the boundary of, the array. These may reach up to 20% during large storm events within the array, but under typical conditions reductions are less than 2% at a distance of 40km from the array. There is no measureable effect on wave conditions at the shore.
Significance of impact on receptors = Not significant
Minimal direct disturbance is caused by HDD and the construction programme for this activity is relatively short in duration (up to a few months).
Significance of impact on receptors = Not significant
No measureable change in water levels (maximum modelled change is 0.007m). Localised flow accelerations around the foundations and wake effects downstream of the foundations (within up to a few hundred metres downstream). Maximum reductions modelled in the range 0.05 – 0.1m/s within the array. Maximum increases modelled to be 0.05m/s within the array. Only very minor changes in flow direction (<5°).
Significance of impact on receptors = Not significant
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