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

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  watching-the-tides/ watching-the-tides/ Tidal period

 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 Why do different places on Earth see different patterns of tides?

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