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Secrets of the St. Lawrence

The wind and the waves - Conflicting seas

Baie des Sept Îles

- "Just look at those waves. And I thought we'd find calmer seas here. Let's get out of here right away."


Live and learn! When waves strike a vertical barrier such as a cliff or a wharf, they are reflected and rebound.

But as they flow back out and meet incoming waves, their crests cross and build quickly, producing a choppy, confused sea up to a few nautical miles offshore. It's not very comfortable for anyone on board.

If you are mathematically inclined, you can use the formula opposite to draw up a chart showing how high the waves will build, depending on the fetch in Baie des Sept Îles.

Reflection - Reflected waves H1 and H2 traveling in opposite directions encounter one another creating a choppy sea surface and a new wave H3. The height of the new wave (H3) caused by the encounter of the two original waves (H1 and H2) can be calculated by finding the square root of the sum of the height of the first wave (H1) square plus the height of the second wave (H2) square.


In such a confused sea, it wouldn't be wise to try to seek shelter near a cape or a point.

When waves approach shoals from an angle, they bend toward the shallows, increasing in height.

In the lee of an island, this refraction effect produces a cross sea. These confused and choppy conditions can make navigation very difficult and even dangerous, depending on the wind speed.

The same cross-sea effect can be produced by refraction when the shoal is an underwater mountain or point.

Refraction - As waves approach a point of land it causes them to bend towards the land creating a concentrated set of waves which focus near the point while the adjacent waves remain relatively unaffected.

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