21.5.1 Hydrogeology 21.5.1.1 Geology
21.5.1.1.1Superficial Deposits 45.
The geology within the study area is described in Chapter 19 Soils, Geology and Ground Conditions, which in summary indicates that superficial deposits beneath the area of the onshore electrical transmission works are either absent or sporadic from the landfall to Great Bealings. Where they do exist they comprise mostly of sand and gravels from the Kesgrave Catchment Subgroup. From Great Bealings westwards towards the converter station superficial deposits become more prevalent comprising chalky till (Lowestoft Formation) over the Kesgrave sands and gravels.
46. Deposits within river valleys change to reflect the environment comprising sandy, silty clay (Alluvium) or Marine and Coastal Zone mud deposits.
21.5.1.1.2Bedrock 47.
48.
The bedrock geology beneath the onshore electrical transmission works generally comprises the following formations in succession from the ground surface:
Red Crag Formation;
Coralline Crag Formation; London Clay Formation;
Lambeth Group and Thanet Sand Formation (undifferentiated); and Chalk Group.
At landfall Red Crag is present at the ground surface and is evident in the sea cliffs. As the onshore electrical transmission works move west the crag formations diminish leaving London Clay and the Lambeth Group and Thanet Sand Formation (undifferentiated) at or near the surface. These too diminish as the onshore electrical transmission works move west and from Claydon the chalk becomes exposed at ground surface, especially in River Gipping valley area.
21.5.1.2 Aquifer Designations 49.
The majority of the superficial drift deposits in the region are defined by the Environment Agency as Secondary A aquifers. These are described as deposits with permeable layers which have the capability to support water supplies at a local rather than strategic scale and provide an important source of base flow to rivers.
50.
The till from the Lowestoft Formation and London Clay formations within the region are defined as unproductive strata. These are deposits with low permeability, and have a negligible significance for water supply or base flow to rivers.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 21 Water Resource and Flood Risk Page 21
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