The 1928 Thames flood was a disastrous flood of the River Thames that affected much of riverside London, England, on 7 January 1928, as well as places further downriver. Fourteen people were drowned in London and thousands were made homeless when flood waters poured over the top of the Thames Embankment and part of the Chelsea Embankment collapsed. It was the last major flood to affect central London and led to the implementation of new flood control measures, culminating in the construction of the Thames Barrier in the 1970s.

During Christmas 1927, heavy snow fell in the Cotswolds in central England, where the Thames has its source. A sudden thaw occurred on 31 December 1927 and 1 January 1928, followed by unusually heavy rain, doubling the volume of water coming down the river. The sudden rise in water level coincided with a high spring tide and a storm surge caused by a major extratropical cyclone in the North Sea. The storm surge raised the water levels in the Thames Estuary, measured at Southend, to 1.5 m (4 ft) above normal.

The funnelling of the water further up the river caused its level to rise even further. The situation was worsened by capital dredging which had been carried out between 1909 and 1928, deepening the river channel by about 2 m (6 ft) to allow deeper-draughted vessels to access the Port of London. This had the side-effect of making it easier for water to access the Thames, increasing the flow on a mean tide by about 4% and raising the tidal range by about 0.7 m (2 ft).

This produced the highest water levels ever recorded in the Thames in London. The flood peaked at about 1.30 a.m. on 7 January when a level of 5.55 m (18 ft 3 in) above the datum line was recorded, nearly a foot higher than the previous record. Extensive flooding resulted as the river overflowed the Embankments from the City of London and Southwark up to Putney and Hammersmith. Serious flooding was also reported in Greenwich, Woolwich and other locations further downriver, causing major property damage.

A considerable area of the city centre was flooded by this unprecedented combination of events. The most serious incident occurred at Millbank, where a 75 ft (25 m) section of the Chelsea Embankment collapsed, sending a wall of water through a generally poor and run-down area. Fourteen people were drowned, unable to escape from the basements in which they were living. Another 4,000 people were made homeless as water filled the streets to a depth of four feet (1.2 m). Elsewhere, the Tate Gallery was flooded to a depth of between five and eight feet (1.5 to 2.8 m), causing extensive damage to its collections.[6] Westminster Hall and the House of Commons were also flooded, as were the London Underground stations and lines along the riverside. The moat at the Tower of London, which had been empty for over 80 years, was refilled by the river, and the Blackwall and Rotherhithe Tunnels were submerged.

Remarkable scenes were witnessed all along the Embankment. At the Houses of Parliament the water "cataracted" over the parapet into the open space at the foot of Big Ben. The floods penetrated into Old Palace Yard, which shortly after one o'clock was about a foot under water in parts.