Friday, July 14, 2017

The 30th Anniversary of the Decarie Expressway flood

Firefighters rescue trapped motorists from the Decarie Expressway after thunderstorms generated historic flash flooding on July 14, 1987. (Radio Canada)
Tuesday, July 14, 1987 dawned hot and humid across southern Quebec, as it had been for the previous week. Montreal recorded high temperatures in excess of 32C (90F) from July 9th through the 14th, including a record high of 34C (94F) on July 13th. Accompanying the high heat was stifling humidity levels. Montreal is a city that is accustomed to very humid summers, but these levels were off the charts. The elevated humidity had saturated the atmosphere, similar to the tropics, not southern Canada. On the morning of July 14th, a strong cold front was lying west of Ottawa. In addition to the the front, low pressure had developed in southeast Ontario. Some partial sunshine early on July 14th in Montreal, allowed the mercury to climb to 30C (86F) before the noon hour, adding fuel to the atmosphere. The air mass had become unstable and volatile, all the conditions were perfect for powerful thunderstorms.

Widespread flooding trapped hundred of motorists in Montreal on July 14, 1987. (Radio Canada)
The storms would first develop southwest of Montreal around 11am, approaching the city shortly afterwards and moving from Chateauguay northeast across the Island of Montreal and into Laval. With plenty of available moisture, the thunderstorms would produce torrential rainfall for several hours, training over the same locations. Four separate thunderstorms cells in total would impact the city from 11am through 3pm. In some cases, a months worth of rainfall would occur in less than 2 hours. Trudeau Airport measured 57.4mm (2.25"), but it was the central portion of the city and the downtown core the would be hardest hit. I lived on the waterfront in Verdun at the time, and my rain gauge overflowed at 100mm (4 inches).

Officially, 102.2mm (4.02") fell at the McGill Observatory on McTavish, 86mm (3.38") of that fell in less than one hour. At Parc Lafontaine, 103mm (4.05") was recorded, with unofficial reports of as much as 180mm (7.1"). The deluge would overwhelm the sewer system, designed for no more than 36mm (1.41") per hour. Water would pour into highway underpasses, basements, businesses and of course the Decarie Expressway. Over 300 motorists became trapped in their vehicles on the Decarie alone, requiring rescue from the Montreal Fire Department. Nearly 400 cars would be abandoned. Traffic was gridlock across the city as major routes such as Highway 20 at 1st Avenue in Lachine and the St Remi Tunnel became flooded as well. The Metro was forced to close as a result of flooding on several lines. The evening commute would last into the wee hours of July 15th.

Flash flooding on Atwater Street in downtown Montreal, July 14, 1987. 
(The Montreal Gazette)
Wind gusts of 80km/h occurred with the thunderstorms, knocking out power to over 350,000 homes. Along with the loss of power, came the loss of air conditioning and electronic pumps. The wind snapped trees and power lines, but it was the rain that created the massive damage. In all, over 40,000 homes in the city sustained some form of water damage. As is often the case, much of it was not covered by insurance. Total losses for the storm exceeded $220 million. Sadly two fatalities were reported, one man drowned in his car in a Cote-des-Neiges underpass, while a second person was electrocuted.

Water pours down Mount Royal Avenue during flash flooding on July 14, 1987. 
(The Montreal Gazette)

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