What is the meaning of a Bore in a River?

A ‘bore’ is a body of water which results out of the exceptionally high sea tides, rushes up rivers. Travelling upstream about two or three times as fast as the normal tidal current, a bore is characterized by several waves, followed by the bore’s main body, which rises higher than the water level at its front. Tidal bores are formed at a short distance upstream, where the channel has become sufficiently narrow.