On August 4th, 2003, intense rainfalls in southwest Quebec triggered flash floods in the Bois Francs Region (Figure 1). The most damaging flooding occurred within an area of about 20 km radius area situated south of Victoriaville. The principal municipalities affected were Tingwick, Warwick, Norbertville, Saint-Fortunat, Victoriaville, and Chesterville (Figure 2).

Figure 1. Southwest Quebec.

Figure 2. Principal municipalities affected.

Figure 3. General view of the Nicolet River valley, Chesterville.

Figure 4. Typical Appalachian rolling hills in Tingwick area.

Between 3:00 pm and 9:00 pm on August 4th, 2003, at least 140 millimeters of rain fell in the vicinity of Victoriaville. In Tingwick, 139 millimeters of rain fell in two hours, including about 80 millimeters of rain in one hour alone. This extreme climatic event is comparable to antecedent climatic events that occurred in the Saguenay Region from 19 to 26 July, 1996, where up to 278 millimeters of rain fell in 48 hours, and in Montreal on July 14th, 1987, where 100 millimeters of rain dropped in 2 hours. Locally, on August 27, 1971, the Victoriaville region experienced severe flooding caused by hurricane "Doria". Damages to roads, bridges, and crops were estimated to $0.25 million (in 1971 dollars) (Emergency Preparedness Canada database, 1997). The rapid response of streams and the typical rolling topography of the Appalachian Mountains (Figure 3) make the plains and wide valleys, such as the Nicolet River valley (Figure 4), vulnerable to flooding.

The extreme storm caused the DesPins, Desrosiers, and Nicolet rivers, as well as small streams draining agricultural lands, to overflow. Severe flooding and important riverbank erosion occured along sections of major streams and rivers, and caused undercutting and damages to bridges and roads, severe damage to buildings and homes, and partial damage to crops. The flooding forced more than 500 residents to abandon their homes temporarily and resulted in the evacuation of 150 people. (Le Devoir, 6 August 2003). Fortunately, no deaths or injuries were reported. However, the road network had been severely damaged: 8 bridges closed, including seven that were washed out. Damages to roads and bridges were estimated between $5 and $7 millions within the municipality of Tingwick alone (Le Devoir, 6 August 2003).

In the 2 or 3 days following this event, regions to the east of the Bois Francs Region experienced intense rainfalls, especially the Saint-Elzéar de Beauce area. In the context of global climate change, more and more interest is being focused towards mitigating the impacts of these extreme climatic events on infrastructure and population. The effects of anticipated climate change could result in changes in flow regime and therefore the frequency and magnitude of floods.

The selected photographs depict the principal impacts of these flash floods on linear infrastructure (e.g. roads, bridges, natural gas pipeline), properties (e.g. houses, cottages, buildings) and agricultural lands.

Author: Réjean Couture