An exceptionally severe and localized rainfall which occurred over the North Antrim Plateau on 1 August 1980 caused major damage to tarmacadam roads and swept a fisherman and his boat half a mile out to sea. Eyewitness accounts are given of this event, which has a return period of about 8,000 years.

Mr. John Young, the Meterological observer at Altnahinch Filters, witnessed and drew attention to an exceptional and very localized fall of rain and hail which occurred on the afternoon of 1 August 1980 in the North Antrim Plateau behind Cushendun in Northern Ireland. This led Mr. S.J.G. Partington, Senior Meteorological Observer at the Climatological Services Meteorological Office in Belfast to interview a number of other witnesses and later to visit the scene.

The downpour commenced at 1630 GMT and ended at 1715 GMT, during which 45 minute period 97.0 mm of precipitation fell at the Orra Beg rainfall station (located at Irish Grid Reference iC143277, altitude 335 m) and 47.0 mm fell at the Orra More, Ballybraddin rainfall station (located at IGR iC125261, alt. 396 m). Daylight was reduced to virtually night-time conditions and hailstones the size of eggs were observed, with the mountainside white, so dense was the coverage. Some lightning was seen and thunder heard at Altnahinch, but the thundery aspect did not feature in the reports from other witnesss interviewed.

It was fortunate that the fall occurred on the 1st of the month, for the two raingauges are read only once a month and had been read and emptied that morning; otherwise the true amount of rainfall would not have been known.

A Mr McNeill, fisherman of Cushendun on the coast, was warned by telephone by some relations living up the valley of the River Dun, that a wall of water was forming, and this prompted him to rush to his boat moored in the estuary so that he might slacken his salmon nets. Whilst he was doing this, he saw this wall of water coming down the river, with an estimated height of between five and ten feet, and when it met the sea, he, in his boat, was swept out to sea about half a mile by the floodwater. This was some time between 1730 and 1800 GMT.

Some 60 metres length of the * Ballymoney - Cushendall road was washed away,one end of the section being moved about 200 metres whilst the other end was washed about 400 metres (see Plates II and III). Two policemen in their patrol car were unable to stop before their car drive into the crater created by this landslip.

The area is a peat bog, laid on a solid rock base. The intense rain created fissures some 3 metres or so deep down to bedrock, and some craters appeared about 250 metres wide in which again all the thick peat was washed away. revealing the bedrock surface (see Plates IV and V).

The magnetic-tape rainfall recorder at Orra Beg, Ballybraddin, was unserviceable at the time, and the next nearest (of the tilting-siphon pattern) at Altnahinch Filters recorded only a small amount of rainfall, it being on the extreme edge of this storm.

The fall of 97.0 mm in 45 minutes is a United Kingdom record fall for that period. If that information is fed into the return period statistical model developed after the United Kingdom Flood Studies Report, the 97 mm in 45 minutes has a return period for that part of Northern Ireland of around 8000 years.

Movements of peat and other debris from the bogs of Northern Ireland are not all that uncommon. The previous significant one known to the author was on 10 November 1963, again in the Glendun area. A list of bogflows was included in the paper 'Recent bogflows and debris slides in the North of Ireland' by Colhoun, Common and Cruickshank in the Scientific Proceedings of the Toyal Dublin Society, Series A, Volume 2, No 10 (1965). Another paper on the subject is 'Composite mudflows on the Antrim coast of North-east Ireland' by Prior, Common and Archer, in Geografiska Annala, Vol. 50, Ser. A, 1968, 2.

We are grateful to Mr. Young for his enthusiasm in returning promptly to the Orra More mountain rain-gauge sites to measure the rainfall of this storm: it is largely from such sources that the Meteorological Office and the former British Rainfall Organization have been able to collect reliable and detailed records of the country and are of such value to those who have to design and operate flood control systems."