September 1968 Floods

London cut off
by Philip Eden

"Floods Devastate South - Hundreds of Homes Evacuated"; that was the front page headline in the Daily Telegraph just over 40 years ago. In fact the date was Monday 16 September, 1968.

This was probably the most severe inland flood to hit the Home Counties in the last 100 years - the North Sea coastal floods of February 1, 1953, were worse, particularly in terms of loss of life. Mercifully, the September 1968 flood took no lives. Things were worst on the Monday and Tuesday by which time water covered roughly 280 sq km of land - that is the equivalent of one-sixth of the area of Surrey - and some 25 thousand homes were flooded.

Indeed, Surrey suffered more than any other county. In Esher alone roughly eight thousand houses, roughly one-third of the urban district's housing stock, had water damage, and a further four thousand properties were similarly affected in the adjacent towns of Walton and Weybridge, Chertsey and Addlestone, and Woking. In Guildford, town-centre shops were flooded to depth of 2.5 metres.

Several road and rail bridges were badly damaged; six of these suffered major collapse and subsequently had to be completely rebuilt. Most of the main roads taking traffic south and west from London were blocked for at least 24 hours (some of them for three days). Farmers suffered considerable losses too, especially those with root crops, although the cereal harvest had been completed by the end of August.

The floods were the result of a prolonged downpour which lasted for the best part of two days. This in turn was caused by a vigorous depression which had become stationary over France; two contrasting air-masses - a very warm and very moist one which had originated over the western Mediterranean, and a cool moist one from the Baltic Sea - converged over southeast England, and the line of convergence moved very little during that astonishingly wet weekend.

This weather pattern bore some similarity to the one which prevailed across Essex, London, Surrey and Hampshire last week (on Tuesday 15th) although this year's event was at least two orders of magnitude less severe than the 1968 event.

Then, a broad belt extending from the New Forest to the Thames Estuary received over 75mm of rain. That is the equivalent of six weeks' worth of rain in less than 48 hours. Some 75mm also fell in a much narrower belt along the line of the Chiltern Hills from south Buckinghamshire across Hertfordshire to west Suffolk. A sizeable are covering much of Surrey, west Kent, southeast London and south Essex was deluged with more than 150mm of rain, and two rainfall-recording sites in Essex - Tilbury and Stifford - received slightly more than 200mm, which is more than they had had during the whole of the summer quarter.