To add to Mark's excellent post these events
have been studied.
Specifically conditions of tidal current
overfalls and abrupt depth
contour upwellings in storm conditions.
You will see more chart notations of "disturbed water
....etc" in regions that have higher tidal ranges than say in the Carribe.
My biggest concern is more to do with opposing surface current
against sea state than 100ft depths.
Here in the Philippine Islands, the different surrounding large bodies of water
ebbing and flowing thru so many islands conflict with each other. This builds up confused seas in channels to far greater heights than one would normally expect for the given wind