The floods in Saguenay

Photo : Jean Briand

Because they couldn't sustain the strain of the strong currents and the rate of flow in the À-Mars River, the smolt population was significantly lowered. On the other hand, the older salmon population fared much better. The floods also destroyed the salmon's fish ladder. It was rebuilt at a cost of 1 390 000 dollars.

La passe migratoire de la
rivière à Mars

Source : Ministère de
l'Environnement de la faunne

The July 1996 torrential rain caused a water swell of rare intensity in the Saguenay region. Many waterways swelled up and some even left their bed, bringing on floods and an escalation of the rate of flow of rivers to levels never seen before.

On top of causing considerable material damage, these events had some negative effects on the marine environment and on the fresh water habitats. But the environmental impacts of the July 1996 floods was probably the aspect which was the hardest to evaluate, measure and quantify.

In the midst of the floods, countless debris was transported by the water, including chemical products, some of which were probably toxic : propane tanks, heating oil, some La Baie district gas station tanks, PCBs, electric transformer oils and lexivia liquid residue from dumping sites. These products, harmful to the environment, were mostly dispersed in the Ha! Ha! Bay and in the Saguenay fjord but, the rate of flow was so great that the polluting agents were completely diluted. Two months after the floods, some oceanographers surveyed the Saguenay river and fjord and found no trace whatsoever of the fore mentioned pollutants.

Photo : Jean Briand

The July 1996 floods had some positive effects on some rivers, which needed to be drained out.

For over a century, most of the Saguenay-Lac-Saint-Jean's rivers were used for wood rafting. The Aux-Sables River in Jonquière was one of them. For all those years, astronomical quantities of wood billets and bark had accumulated at the bottom of the river, causing some pollution. During the floods, the rate of flow of the Aux-Sables River was 15 times greater than usual. Thanks to the sheer force of the water, the riverbed was completely cleaned up and the wood billets at the bottom of the river were suddenly washed up on shore. Over 5 000 wood cords were retrieved, not counting the 5 000 truckloads of bark.

Normally, around 3 millimetres of sediments per year are deposited at the bottom of the Ha! Ha! Bay. In just a few days, in July 1996, 25 to 50 centimetres were deposited in some areas, which is the equivalent of 75 to 150 years of sedimentation! In all, 9 million cu. Metres of sediments were carried during the floods.

Station Depth (m)  Thickness of sediments (cm)
Sag-34 14 5 - 10
Sag-05 65 5 - 10
Baie des Ha! Ha! 150 ~ 30
Sag-15 210 5 - 10
Sag-30 270 < 0,5
Sag-36 234 < 0,5

The tons of sediments deposited at the bottom of the Ha! Ha! Bay and in the Saguenay River rapidly buried the benthos, organism living in the seabed and serving as food to some species of fish. Fortunately, this was short lived, because benthos is very resilient. These organisms rapidly came back up to the sediment surface. Pertaining to the other species living in this marine environment like the Snow crab and the pink shrimp, because great mobility, they weren't buried. The positive impact of the sediments is that they were deposited onto older contaminated sediments that had accumulated because of the aluminium and paper plants in the 50s, 60s and 70s.

The sediments deposited at the bottom of the rivers provoked the silt-up of the Atlantic salmon spawning sites. The sediments would choke-up the nests and prevented the fish eggs from growing. The sediments also covered up the insect larvae, the Atlantic salmon's main food source.

Sediments deposited at the bottom of the À-Mars River buried many salmon pits. Before the floods of July 1996, around 40 pits could be counted. A few days after the events, there were only 25 left. Today, thanks to the efforts made by the "Fondation de la faune du Québec", the river got its pits back.

The strong rate of flow of the water eroded the riverbanks, bringing on the disappearance of trees and shrubs near the rivers, thus depriving the fish of shelter, shadow and food.

Under the impact of the flooding water, a dyke located on the Ha! Ha! barrier lake gave way. All the water streamed towards the Saguenay River using the Ha! Ha! River. 15 million cu. Metres of the Ha! Ha! barrier lake's 23 million cu. Metres passed in the river. As a result, the big and small Ha! Ha! lakes were almost completely emptied. This massive water flow resulted in an important drop in some of the fish population like the speckled trout, red charr and the white sucker. There was also a major drop in the quantity of food for the surviving fish population.