How does a tidal bore form in a gulf or bay?

A tidal bore does not typically form within a gulf or bay itself; rather, it is a phenomenon that occurs in rivers and estuaries that empty into such coastal features.

A tidal bore forms when a large tidal range—often amplified by the funnel shape of a gulf or bay—forces an incoming tide into a narrow river channel. In funnel-shaped gulfs, the depth gradually decreases headward, which can cause resonant tides that result in a tidal range significantly greater than that of the open ocean.12

When this powerful flood tide enters a river, the incoming water is confined to a narrow channel, creating a steep wave or "wall of water" that travels rapidly upstream. This process is most common during spring tides, where the momentum of the incoming tide overcomes the outward flow of the river, abruptly changing the direction of the water current. A well-known example of this interaction occurs at the Petitcodiac River, which empties into the Bay of Fundy, a region famous for having the world's maximum tidal range.12