When is the best time to go beachcombing or tide pooling?

1
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?v99-9mnCMahA
• 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

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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.nwsourc
e.com/html/localnews/2009284656_sewage01m.html
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An Introduction to Tides
Tidal period

• 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

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What type of tide do we see along the WA coast
crest
trough
5
Why do we have tides?

• http//www.youtube.com/watch?vCTQ6ciHENgI
• Gravitational attraction between the sun and moon
• Earth-Moon system is held in orbit about the sun
  by the Suns 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
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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

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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 Earths oceans
• tidal bulges on opposite sites of the planet

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Why do we have tides?
Fig. 11.5

• Change in water level at A during one earth
  rotation

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What are spring tides? Neap tides?

• The gravitational pull of the moon and the sun
  affect the Earths 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
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When is high tide? When is low tide?

• NOAA Tide Prediction
• Port Angeles

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When is low tide? High tide?
Flood
Ebb
Slack
LLW
Slack tide? Change of direction, between ebb and
flood
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When is low tide?
Tidal Period? Time from crest to crest or trough
to trough
Tidal Day?
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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?

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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.
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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
• Dont confuse tidal day and tidal period

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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

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

• Three basic tidal patterns occur along the
  Earths 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

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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

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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
  Earths 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

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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

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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

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Tidal Tips

• Know 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.