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 http://www.youtube.com/watch?v=99-9mnCMahA

How to read Tide Tables Patterns or types of tides http://tidesandcurrents.noaa.gov/

Maritime activities throughout the world depend on accurate tidal and current information for safe operation

Tides in the news…

Raw sewage pouring into harbor off Bainbridge Island

A major sewage pipe that ruptured Saturday on Bainbridge Island continued to spill tens of thousands of gallons of raw waste into Eagle Habour...

By Drew DeSilver, Seattle Times staff reporter, June 2, 2009

“A major sewage pipe that ruptured Saturday on Bainbridge Island continued to spill tens of thousands of gallons of raw waste into Eagle Harbor today, and a city official said the line can't be fixed until Tuesday morning.”

“The pipe runs about four feet underneath the beach, about 1,000 feet from the ferry terminal. It's underwater except during low tides; crews had to dig it up Sunday morning to examine the damage.”

Read the full article: http://seattletimes.nwsource.com/html/localnews/2009284656_sewage01m.html

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

When the crest of the wave reaches a particular location, high tide occurs

Low tide corresponds to the trough

The difference in height between high and low tide is the tidal range

Tidal period

What type of tide do we see along the WA coast

crest

trough

Why do we have tides?

http://www.youtube.com/watch?v=CTQ6ciHENgI

Gravitational attraction between the sun and moon Earth-Moon system is held in

orbit about the sun by the Sun’s gravitational attraction (A)

Centrifugal forces Pulls the Earth moon system

away from the sun

Gravitational and centrifugal forces act to keep the Earth-Moon system in balance Forces are equal and opposite

Fig. 11.3

Why do we have tides?

Gravitational attraction

Tide generating force = G(mass/distance3 ), G = universal gravitation constant

sun: 27 times larger than moon, but 390 times further from earth Sun tide is 46% of moon

tide

Why do we have tides? Centrifugal force

Acts in opposite direction to gravity and is equal to gravity to keep orbiting bodies apart

Gravity and centrifugal force act in opposition on the Earth’s oceans tidal bulges on opposite sites of the planet

Tidal bulge due to centrifugal force

Why do we have tides?

Change in water level at A during one earth rotation

Fig. 11.5

What are spring tides? Neap tides? The gravitational pull of the moon and

the sun affect the Earth’s tides on a monthly basis

When the sun, moon, and Earth are in alignment (at the time of the new or full moon), the solar tide has an additive effect on the lunar tide, creating extra-high high tides, and very low, low tides -- spring tides

One week later, when the sun and moon are at right angles to each other, the solar tide partially cancels out the lunar tide and produces moderate tides -- neap tides.

During each lunar month, two sets of spring and two sets of neap tides See Fig.

11.7

When is high tide? When is low tide?

NOAA Tide Prediction

Port Angeles

When is low tide? High tide?

HHW

HLW

LHW

LLW

Slack tide? Change of direction, between ebb and flood

Flood Tide? Rising tide, landward flow

Ebb Tide? Falling tide, seaward flow

Flood Ebb

Slack

When is low tide?

Tidal Period? Time from crest to crest or trough to trough

Tidal Day?

Tidal Currents

Tidal currents are the horizontal movement of water that accompanies the rising and falling of the tide Incoming tide along the coast and into the bays and estuaries is

called a flood current/tide Outgoing tide is called an ebb current/tide

The strongest flood and ebb currents usually occur before or near the time of the high and low tides In the open ocean tidal currents are relatively weak Near estuary entrances, narrow straits and inlets, the speed of

tidal currents can reach up to several kilometers per hour

Stronger currents during spring tides or neap 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.

Frequency of tides: What is a tidal day?

Tidal day = 24 hours and 50 minutes

This occurs because the moon revolves around the Earth in the same direction that the Earth is rotating on its axis It takes the Earth an extra 50

minutes to “catch up” to the moon

Explains why tides occur about one hour later each day

Don’t confuse tidal day and tidal period

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

As the moon revolves around the Earth, its angle increases and decreases in relation to the equator – declination

Tidal bulges track the changes in lunar and solar declination, also increasing or decreasing their angles to the equator

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?

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?

What Affects Tides in Addition to the Sun and Moon?

Distances and positions of the sun, moon and Earth all affect the size and magnitude of the Earth’s two tidal bulges

The magnitude of tides can be strongly influenced by the shape of the shoreline When oceanic tidal bulges hit coastlines, the height of the tides can

be magnified Conversely, mid-oceanic islands typically experience very small tides

of 3 feet or less

The shape and depths of bays estuaries and inlets also can magnify the intensity of tides Estuaries with strong tidal rivers, such as the Columbia River,

powerful seasonal river flows in the spring can severely alter or mask the incoming tide.

Local wind and weather patterns also can affect tides

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

Tidal TipsKnow the tides before visiting the beach. You can be stranded on a spit or in a cove if you aren't aware of a rising tide.

Avoid walking on logs or climbing bluffs. Loose logs can roll and bluffs can slide.

Watch out for boat wakes. Ferries and speed boats can create large waves.