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About Delta
Tides
Tides on the west coast of Northern America
typically occur in a modified semidiurnal pattern (remember this
phrase so you can impress your fellow anglers) called a mixed
tide. This is where there are two highs and two low tides a day
but the heights of the two successive highs are not the same,
similarly for the two successive lows.
The time and cyclical regularity of the tides
can be explained primarily by the harmonic effect of the moon
and the sun on the earth. Other factors such as topography of
the channel also come into play. Experience has shown that the
heights of both high and low tides could be higher than
predicted due to unusually strong onshore winds, a low
barometric pressure or high river runoff. Conversely, the
opposite could be true for strong offshore winds, a rising
barometer or unusually low river levels.
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