Booms Complementing Icebreakers

2015-10-26

Marc Savard

By partially or completely obstructing a watercourse, an ice jam often causes significant flooding in areas near the shores. This phenomenon has been noted on the St. Lawrence River several times, causing damage to properties on the shoreline.

In the winter of 1992-1993, a major ice jam formed on the river, from Lake Saint-Pierre to upstream of Sorel. The accumulation of ice was so significant that commercial shipping was interrupted for 30 days. There was also considerable damage caused to shoreline properties from rising water.

After this incident, the Canadian Coast Guard added the deployment of steel structures called booms to its ice cover management strategy at Lake Saint-Pierre (Yamachiche) and at Lavaltrie and Lanoraie, with the aim of reducing the risk of flooding in communities located between Lake Saint-Pierre and Montreal. Thus, since 1994, ice retaining structures are deployed to promote formation of a solid and stable ice cover upstream of the ice retention structures. The stable ice cover insulates the water from the cold air, reducing the risk of producing new ice that could end up in the navigation channel. As a result, the navigation channel can remain open during winter.

Before the winter of 1992-1993, booms were installed at Lavaltrie, Lanoraie and Yamachiche, but they had a different configuration that was less effective. At that time, the booms were made of wood beams, which today have been replaced by steel tubes with a diameter of 0.61 m and a length of 9.144 m, closed at each end. A wood beam had a life span of a few years, while a metal beam, when well maintained, has a life span of over 30 years. These beams are secured in groups of 11, through a steel section cable with a diameter of 51 mm and a length of 152.4 m. These steel section cables are in turn connected to 51 mm diameter anchor cables with a length of 76 m. The entire structure is held by several anchors buried in the river bed. The boom at Lavaltrie has a length of 1.1 km, that of Lanoraie 1.3 km while that of Yamachiche is 2.44 km long.

In conjunction with the work of ice-breakers, the booms reduce the risk of ice jams by promoting good ice clearance from the navigation channel, making winter navigation safer.