![]() "Once this condition has been reached, the tidal crest sweeps into the estuary as a conspicuous wave or even as a frothy front - the tidal bore - following the passage of which the water levels inside and outside of the estuary remain more nearly equal." (von Arx) But the rising tide deepens the water and increases the wave velocity until it exceeds the river's outflow velocity. This can effectively create a block of the incoming tide at the depth where the incoming wave velocity is equal to the river's outflow velocity. ![]() In a shallow estuary, it is possible for the wave velocity to be slower than the outflow velocity from the river. ![]() As it slows, the waves become steeper in the fashion of general ocean waves. The limiting case expressions for the "celerity" or wave velocity with respect to the water areįrom the shallow water velocity expression, you can see that the wave slows down as it approaches the shore in progressively shallower water. The wavelength of tidal waves is longer than the depth of the shallow water near the shore, so they move shoreward with a velocity that depends upon the water depth. The precondition for the creation of a tidal bore is the existence of an outflow current speed from the mouth of a river that exceeds the incoming speed of waves from the ocean associated with the incoming tide. ![]() Called a "tidal bore", this wave illustrates the depth dependance of the wave velocity of waves from the ocean. The interaction of the tide with the outgoing current from a river can sometimes produce an unusual solitary wave that proceeds up the river from its mouth. ![]()
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