Geology Site Account

Site of geological interest with potential for promotion of geology. Of educational interest only

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Opened in 1984, and pictured on the front cover of the latest (2004) Geological Survey Memoir for the London District, the Thames Barrier is an impressive civil engineering achievement. Extending across the river at Woolwich Reach, the barrier is part of Londons defences against the risk of flooding and comprises a series of giant movable gates which can be closed when an exceptional high tide is expected. The level of high tides in the Thames Estuary has been steadily rising and since the severe east coast flooding of 1953 it has been recognised that there was a need to improve Londons flood defences. The increasing flood risk is due to rising sea levels as a result of global warming combined with the fact that South-East England is slowly sinking leading to an increase in the tidal range. Tide records indicate an alarming 8 millimetre per year rise in the level of the Thames Estuary.

Design and construction of the Thames Barrier has been well documented. Because the design of the piers, sills, gates and machinery could not tolerate any movement in the foundations the ground investigations had to be extremely thorough. Seventy three boreholes were sunk which revealed that the northern half of the site is underlain by Thanet Sand and the southern half by Upper Chalk. Fortunately the chalk bedrock was below that affected by periglacial activity (i.e. permafrost conditions) during the Ice Age which has turned the surface of the Chalk elsewhere into an unstable rubble by frost shattering. However, some difficulties were encountered such as minor faults with lateral and vertical displacements of up to 50 meters and 5 metres respectively. The Thames Barrier, in fact, sits astride the Greenwich Fault, a major fracture in the deep bedrock of the region. The Greenwich Fault passes across the northern limb of the Greenwich Anticline and continues north-east into Essex where it is known as the Wickham Bishops Fault. This fault is thought to have been responsible for the Essex Earthquake of 1884 and so seismic studies were carried out as part of the investigations which concluded that there was insignificant risk of further tremors in the area arising from this fault.

The Thames barrier has a visitor centre and a terrace café on the south bank of the river.