The floods in Saguenay

The aux-Sables River is Jonquière district's main waterway. Its rate of flow during the flood went from a normal 55 m3/s to over 660 m3/s. The riverbanks considerably swelled up and he riverbed dug itself in more than fifteen metres deeper.

The floods hit the Saguenay's heavy industries. Damages to the infrastructures and the loss of revenues were estimated at around 200 million dollars. The Jonquière district Alcan plant alone sustained damages of over 75 million dollars.
Specialised in the
production of
cardboard, the
Cascades factory
sustained damages on the water
supply point and to the
secondary water treatment
system costing around 10 million
dollars, this is not including the
losses in sales and unpaid
salaries. The factory had to stop
its operations for 10 days.

The water supply point and hydroelectric installations of the Abitibi-Consolidated plant were completely torn out. The reconstruction of the damaged installations cost over 30 million dollars.

The force of the Jean Deschêne stream current completely washed out the ground under Deschêne Street , uncovering a part of the natural gas conduit.

Many sectors were hit in the Jonquière district, most particularly those where industrial infrastructures were to be found. Many installations had to slow down their operations, even as much as shutting them down for periods going from a few days to almost a month. For instance, the Vaudreuil-Alcan industrial complex stopped production for 15 days because of a water supply problem brought on by the destruction of the pumping station.

In the Jonquière district, the floods' main hot spots concerned certain dykes located on the Kénogami barrier lake.

In the Jonquière district alone, 147 apartments were destroyed on top of around a hundred more which were damaged.

Source : Technical Services, Jonquière District

The heaviest rain fell in the Laurentian wildlife reserve, mainly to the South of the Kénogami barrier lake. The precipitation exceeded 200 millimetres in 72 hours. This torrential downpour which fell in less than three days, went well over the average of precipitation generally recorded for the month of July. The monthly average being of 125 millimetres for the area of the Kénogami reservoir.

It was over the Kénogami barrier lake watershed that the precipitation was most impressive,
279 millimetres.

The Kénogami barrier lake drains a watershed 60 times larger than its own area. In other words, if one centimetre falls on the sector, it is almost 60 centimetres of extra water, which is then accumulated in the barrier lake. So now, imagine that in less than three days, 580 million cu. Metres of rain were added to the 384 million cu. Metres already packed into the Kénogami basin. As a result, 1 360 cu. Metres per second were being engulfed in the Kénogami barrier lake. Even if it had been emptied, and if all its dams and its dykes had been nine metres higher, it wouldn't have been able to stock up all of that water.

In the Kénogami barrier lake, the problem consisted in the arrival of great amounts of water, larger than the evacuation capacity of the river.

The Kénogami barrier lake was threatening to bypass a dyke located near the Pibrac dam, the Creek Outlet #1 through the dried up Jean Deschênes stream. The waters dug into the dyke's embankment work, but fortunately, its concrete core remained intact. This small wall saved the Arvida sector from the catastrophe. In fact, the torrent was threatening to move towards the Alcan plant. If the water had been in contact with molten aluminium it would certainly have resulted in a major explosion.

In the Jonquière district, much damage was caused by the swelling up of the aux-Sables River, the latter caused by the extra water contained in the Kénogami barrier lake. Many of the containment dams and dykes built on the barrier lake controlled the rate of flow of the aux-Sables River, more precisely the East-Pibrac and the West-Pibrac dams. Downstream on the aux-Sables River, the Jonquière, Ville de Jonquière and Bésy dams controlled the rate of flow of the river.

East-Pibrac and West-Pibrac damsOn a five-day period, up to 660 cu. Metres per second of water was evacuated from the East-Pibrac and West-Pibrac dams.

In the Jonquière district, the water supply network was completely cut off, affecting 40% of the city's fresh water supply. Located on the side of the Chicoutimi River, the water supply point found itself submerged because of the strong current causing the erosion of the riverside. A makeshift water supply point was set up twelve hours later.

A small 20-centimetre water supply duct stood up to the floods, fortunately for some residents of the Jonquière district. Thanks to this, a whole sector could rapidly be supplied with fresh water.
La prise d'eau
de l'arrondissement Jonquière
Photo : Hydro-Québec

Downstream from the Jonquière dam, the district owns a small power station on the aux-Sables River. The July 1996 floods seriously damaged the power station, bringing on important quantities of debris, sand and rocks inside the building. All the electric equipment was replaced and the turbine had sustained major damages because of the water.

In order to evacuate as much water as possible from the Jonquière dam, five of the floodgates were completely opened and three others at 90%. However, the flow of the water was rendered difficult because of the debris accumulating in front of the dam. Even though it has an evacuation capacity of 1 000 cu. Metres per second, the water succeeded in bypassing it. The flow was making its way by passing on the left bank of the river. On top of this, a breech of around 20 metres large had opened up in the concrete right wing of the dam. A the height of the floods, over 3 000 people of the Jonquière district had their electricity cut off.

On the morning of July 21st 1996, devastation at the small power station distribution point of the Jonquière district.

Over 4 million dollars were needed to rebuild the Jonquière district mini-power station. Today, with its 4 megawatts of power, it still supplies hundreds of homes in the Jonquière district.

Photo : Steeve Tremblay
At the top of the floods, 2800 people had no electricity. So that the largest number of residents could recover the service rapidly, a new electric distribution line was erected.

Photo : Steeve Tremblay