An Environment Agency animation video showing the probable extent of tidal flooding in the River Thames, in the event of an "extreme flooding", without flood defences :
Thames Barrier
The Thames Barrier is part of a network of flood defences in London, designed to protect homes, businesses and nature habitats in the Thames Estuary floodplains.
The network of flood defences are operated and maintained by the Environment Agency
The Thames Barrier became operational in 1982. It was planned, designed and built with an expected life-cycle of 50 years, that is, until 2030.
The Thames Estuary (TE) 2100 project, approved by Defra in 2010, estimated that with climate change and the resultant sea and river level rise, the Thames Barrier would remain effective against flooding until 2070. [BBC News report, 2009, Thames Barrier here to stay]
The Flood in London (December 2013 - February 2014)
Gale force-winds, heavy rain, storms, broken flood defences, flooded homes and business, not to mention damages to railway lines. England had its wettest January since 1766.
Watching flood water gushing through parts of London and other parts of the UK was terrifying.
Listening and watching the angry anxiety, dismayed helplessness of people the flood had directly affected was humbling and emotionally numbing.
The Thames Barrier is an integral part of a network of flood defences in London. The flood defences include:
more than 36 industrial floodgates protecting riverside industry
380 smaller, moveable flood defences
the Thames Barrier is also responsible for a dropdown barrier at Barking and three other large scale barriers located at the Royal Docks.
The future
The Environment Agency Flooding in England & Wales, currently (20th February 2014, 19:45 hrs) has
2 Severe Flood warnings
70 Flood warnings
120 Flood alerts
in place - http://www.environment-agency.gov.uk/
It is perhaps too early for a full analyses of the flood impacts or to expects answers from the relevant organisations as to how the flood happened or could have been better managed.
It is unlikely that the recent floods were foreseen in the Thames Estuary 2100 (TE2100 plan), http://www.environment-agency.gov.uk/homeandleisure/floods/125045.aspx
The Royal Academy of Engineers will hold an event on "Lessons learned in managing the winter floods", on 25th February 2014. This implies a starting point for analyses and answers.