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Tidal Currents
Introduction
In navigation, the effect of the tidal current is often of more importance
than the changing depth due to the tide; in fact, many mariners speak of
"the tide" when they actually have the flow of the tidal current in mind.
Currents can be defined as the horizontal movement of water, and may
be classified as either tidal or nontidal.
Tidal Currents. These currents are caused by gravitational interactions
between the Sun, Moon, and Earth just like the vertical rise and fall
called tide, which we have discussed. Study the terms associated with
tidal currents.
Term
Flood
Current
Ebb
Current
Slack
Water
Definition
When the horizontal movement of water is
toward shore or up a tidal river or estuary, the
current is said to be flooding.
When the horizontal movement of water is away
from shore or down a tidal river or estuary, the
current is said to be ebbing.
The period of time where there is little or no
current is called the minimum before flood or
ebb.
Duration of The interval of time in which a tidal current is
Flood
flooding.
Duration of The interval in which the current is ebbing. In a
Ebb
normal semidiurnal tidal current, the duration of
flood and duration of ebb will each be
approximately 6 hours, but can vary.
Set
The direction of the current is called SET, and is
expressed in the direction TOWARD which the
current flows.
Speed of
The velocity of the current is called speed of
Current or
current and is sometimes referred to as drift.
Drift
7-16
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