Dam failures had minor consequences
The results were clear. In both floods, the failed beaver dams had only a small and short-lived effect on water levels downstream.
During the 2011 flood, the dam failure raised river levels near the inn by only about 20 centimetres — and for just a few minutes. Even if the dam had remained intact, the river would still have overflowed because of the extreme rainfall, according to the researchers.
When they modelled beaver ponds containing four times the observed water volume, the flooding was still minimal. Only unrealistically high dams could have made a meaningful difference, the researchers said.
Log jams a likelier culprit
The study also found that the river’s steep slope, combined with intense rainfall, naturally created fast-moving water, capable of eroding banks and moving large logs. Fallen trees and other kinds of wood jams near bridges were likely a much bigger factor in the flooding and damage than beaver dams far upstream.
These conditions alone were enough to explain the dramatic “walls of water” cascading down the river towards the inn, as witnesses reported.
“We don’t want rivers to be canals, with the same shape and depth — we want trees and beaver dams. It would be completely counterproductive to remove them, and impossible anyway,“ Biron says.
“When we see something incorrect, scientists feel it is our duty speak out, especially when there are legal implications. The wording in Article 105 is key, so lawyers need to be involved, not just scientists.”
The study was co-written by Jean Gauthier and Mathieu Dubé of Tetra Tech QI, inc., Thomas Buffin Bélanger at Université du Québec à Rimouski and Maxime Boivin at Université du Québec à Chicoutimi.
Read the cited paper: “Beaver dam failures: Reconciling science, perception and policy for sustainable river management in Quebec (Canada)