Following upon the severe flooding from an exceptional tide cum surge in February 1953 a removable flood barrier in Long Reach was considered as the basis of a flood defence system compatible with the navigation interests yet avoiding the high cost of bank raising in the metropolis. Three designs of barrier were developed and costed, each embodying two 150 m wide navigation openings. The preferred system incorporated drop gates supported on high towers above shipping when not in use. The navigation authorities ruled that an unobstructed opening at 425 m was necessary and a new design exercise found in favour of retractable barrier structures but at increased cost with less reliability in performance. The formation of the Greater London Council led to a wider investigation of possible barrier sites and the lesser use by shipping of reaches above the Royal Docks permitted narrower openings. Schemes for some six different sites and over 40 variations in span arrangement were investigated and led to a proposal for four 60 m navigation openings in Woolwich Reach which might be closed by a form of rising section gate. This has proved to be the cheapest, most reliable and quickest to install of all the schemes investigated and is now the basis of design for contract.