Tides
Learning Targets:
I can define tides and their
importance.
I can describe what influences tides.
I can differentiate among the
different types of tidal patterns.
When is the best time to go
beachcombing or tide pooling?
 High tide or low tide?
 Better check the tide tables before you head to
the beach
Tidal period
An Introduction to Tides
 Tides are the rise and fall of sea level caused by the combined
effect or rotation of the Earth and the gravitation of the Moon
and Sun.
 Tides are long period waves that begin in open ocean and
move toward shore, resulting in the rise and fall of sea level
 Crest of the tidal wave = high tide
 Trough of the tidal wave = low tide
 http://science.kqed.org/quest/video/science-on-the-spotwatching-the-tides/
Why do different places on Earth see
different patterns of tides?
 Continents block the westward passage of the tidal bulges as the
Earth rotates
 Unable to move freely around the globe, these tides establish
complex patterns within each ocean basin
Why do different places on Earth see
different patterns of tides?
 Three basic tidal patterns occur
along the Earth’s major shorelines
 Most areas have two high tides
and two low tides each day
 Semidiurnal – two highs and lows
are about the same height
 Mixed Semidiurnal – highs and
lows tides differ in height
 Diurnal – one high and one low
tide each day
Harnessing Tides: Tidal Power
 Hydropower that converts the
energy of tides into electricity or
other useful forms of power
 Tidal energy is generated by the
relative motion of the water which
interact via gravity
 Renewable
 More predictable than wind or solar
The world's first
commercial axial
turbine tidal stream
generator — SeaGen
— in Strangford Lough.
The strong wake shows
the power in the tidal
current.
Be Aware of Tides in Puget Sound
 The shape of Puget Sound affects
the tide as it moves through
channels and inlets
 In the Straight of Juan De Fuca, a 7.2
foot tide at Cape Flattery will reach
Port Townsend 3 hours and forty
minutes later and increase in
magnitude to 7.9 feet
 The tide will reach south Puget Sound
1 hour later and increase to 13.5 feet
by the time the tide reaches
Olympia
 Extreme high tides of 18 feet have
been recorded in Olympia
Tides create strong currents
 In Puget Sound, the tide rushes through narrow channels
and around islands creating rapids and eddies like a
whitewater river
 It is important for boaters and beach explorers to know
what the tide is doing
 Some waters are not navigable at low tide
 Some beaches may also be hazardous