The 1920 Louth flood was a severe flash flooding event in the Lincolnshire market town of Louth which occurred 29 May 1920, resulting in 23 fatalities in 20 minutes. It has been described as one of the most significant flood disasters in Britain and Ireland during the 20th century.^[1]

The last week of May 1920 saw generally hot weather across the UK, with numerous thunderstorms developing particularly in England.^[2] The three days before the 29 May had been wet across the Louth area, which left fields waterlogged and the ground saturated.^[3]

The flood disaster shocked the nation, with newspapers widely covering the story, and questions raised in the House of Commons regarding the suddenness of the flood, its severity and the forecast.^[9] The event was widely covered in the press as it occurred just before the 1920 Louth by-election, held just 5 days after the flood.^[10] Many people died as they were trapped on the ground floor,^[11] deaths included four firemen swept away with their engine.^[11]

The river Lud at Louth is known to be a "rapid response" catchment, draining an area of 52km².^[12][5] Louth has a low flood frequency, and the behaviour of chalk catchments is not well known, which has hindered assessment of the risk to the town.^[5] As a catchment on chalk the Lud is more likely to be affected by high intensity short summer storms, rather than prolonged winter flooding.^[5]

It has been claimed that Lud had not previously been known to flood,^[5] though records exist for a flood on 10 January 1857.^[5] The river in the town has been known to have deadly flooding before in 1351 and in 1571.^[3] The estimated return period of the 1857 flood is 1 in 300 years, and 1920 flood a return period of 5000 years.^[5]

Other, less devastating and non-fatal floods occurred on 25 June and 20 July during the 2007 United Kingdom floods.

A recent investigation found that the storm rainfall was badly underestimated and that the peak discharge was marginally underestimated. When the revised discharge is put into the context of measured flow at Louth it is seen that similar events can and will occur in the future.^[5] The river course through the town still faces several obstructions, such as low bridges.^[5] Though the railway in town closed in 1980, in places embankments removed which may ease water flow through the town.

• Robinson, D. N., 2000. The Louth Flood 29 May 1920. Louth Naturalists' Antiquarian & Literary Society, 2nd edition, 48pp.
• Account of flooding by 15 year-old boarder at King Edward's School