tidal powerrrs

8/17/2019 Tidal Powerrrs

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Physical Oceanography

Tides


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Tides

• What are the characteristics and causes of

tides?

– Tides are caused by the gravitational force ofthe moon and sun and the motion of earth.

– The wavelength of tides can be half the

circumference of earth.

– Tides are forced waves because they are neverfree of the forces that cause them.


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© 2002 Brooks/Cole, a division of Thomson Learning, Inc.

The Euilibrium Theory of Tides

The action of gravity and inertia on particles at five different locations onEarth. Forces are balanced only at point CE, the center of Earth. Note thebulges that are aligned with the moon as Earth spins on its axis. The keyto understanding the equilibrium theory of tides is to see Earth turning

beneath these bulges.


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Euilibrium Tidal Theory

• !oon Tide – Produced by the moon"s gravitation force on

water

– # bulge of water is created by the moon"sgravitational force

– $entrifugal forces produces a bulge on theopposite side of the Earth

– $reates an area of low water between the tidal bulges

– The Earth ma%es one rotation in &' hours


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Tidal (ay

• # lunar day is the time that elapses between whenthe moon is directly overhead and the ne)t time themoon is directly overhead.

• (uring one complete rotation of Earth *the &'+hoursolar day, the moon moves eastward -&.& degreesand Earth must rotate an additional /0 minutes to

place the moon in the e)act same position overhead.

• Thus a lunar day is &' hours /0 minutes long.• E)plains why tides arrive at any location 1 one hour

later each day


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2pring and 3eap Tides

• 2pring Tides

– (uring the period of a new

moon the moon and sun

are lined up on the same

side of the Earth – Produces the greatest range

between high water and low

water

• 3eap Tides

– Produced when the moon is

at a right angle to the line of

centers of the Earth and the

sun – The range between high

and low water is small


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© 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Tide Patterns

Tide curves for three common types of tides.


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Tide Patterns

The worldwide distribution of the three tidal patterns.


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E)amples of monthly

tidal curves

Top5 6oston !assachusetts

showing semidiurnal tidal pattern.

7pper middle5 2an 8rancisco

$alifornia showing mi)ed tidal

pattern with strong diurnal

tendencies.

6ottom5 Pa%hoi $hina showing

diurnal tidal pattern.

Tide Patterns


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Tide Patterns

• #mphidromic Points

– # 9no+tide9 point in an ocean

– #bout a do:en amphidromic points e)ist in theworld ocean.

– 2ometimes called

a node.


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Tides in $onfined 6asins

• 4ow do tides behave in confined basins?

• The tidal range is determined by basin

configuration

.


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Tides in a narrow basin. Note that a true amphidromic system does not

develop because space for rotation is not available.

Tides in $onfined 6asins


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Tides in a $onfined 6asin

• Tidal ranges vary across the ocean basin

• ;argest variations occur at the edges

– Especially in bays and inlets – Energy is concentrated in a small area

• # mini amphidromic system develops

• E)treme tides in areas where there arenatural oscillation periods of -& or &' hours


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The largest tidal range in the

world occurs in 3ova 2cotia meters */= feet, oftenstranding ships.


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6ay of 8undy 4igh Tide

6ay of 8undy ;ow Tide


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Tides in a $onfined 6asin

• Tidal 6ore – # high often brea%ing

wave generated by a

tide crest thatadvances rapidly up anestuary or river

– Occurs in inlets and

some rivers e)posed togreat tidal fluctuations

– # true tidal wave


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Tide ;evels

• 4igh water

– reatest height that the tide reaches in a day

• ;ow water – ;owest level that the tide reaches in a day


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Tide ;evels

• !ean tide

– $alculated by ta%ing the average of all the

changes in water level over several years

• 8lood tide

– Tide is rising

•Ebb tide – Tide is falling


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Tidal $urrents

• !ass flow of waterinduced by theraising or lowering

of sea level owingto passage of tidalcrests or troughs

• Ebb current

• 8lood current

• 2lac% water


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Tides and !arine Organisms

• @ntertidal Aone – Where the land and

sea meet between the

high and low tide:ones.

– Organisms that livehere are adapted tohuge daily changes inmoisture temperatureturbulence *from thewater, and salinity.


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Tides and !arine Organisms

• runionsB * Leuresthes tenuis,

– 2pawn from late 8ebruary to early 2eptember


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E)pected runion Cuns for &00/

CLOSED SEASON

OBSERVATION ONLY

May

-0 Tu -05'/ P! + -&5'/ #!D

-- We --5&0 P! + -5&0 #!D

-& Th -&500 #!D + &500 #!D

- 8r -&5'/ #!D + &5'/ #!D

&/ We -05'/ P! + -&5'/ #!D

&= Th --5/ P! + -5/ #!D&> 8r -&5/ #!D + &5/ #!D&F 2a -5/0 #!D + 5/0 #!D

OPEN SEASON

June

F We -05&/ P! + -&5&/ #!DG Th --500 P! + -500 #!D-0 8r --5'0 P! + -5'0 #!D

-- 2a -&5&0 #!D + &5&0 #!D

& Th -05'0 P! + -&5'0 #!D&' 8r --5/ P! + -5/ #!D&/ 2a -&50 #!D + &50 #!D&= 2u -5/ #!D + 5/ #!D

Where the time relating to the e)pected run is after midnight the date of the previous

evening is shown. + http5HHwww.dfg.ca.govHmrdHgruschd.html

http://www.dfg.ca.gov/mrd/gruschd.htmlhttp://www.dfg.ca.gov/mrd/gruschd.htmlhttp://www.dfg.ca.gov/mrd/gruschd.html


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Tidal Power

• Tidal energy can be e)ploited in two ways5

– 6y building semi+permeable undersea tidal

turbines across estuaries with a high tidal range.

– 6y harnessing offshore tidal streams


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Tidal Power

• 4ow it wor%s5

– Water flow as basin fills or

empties drives turbines – 2imilar to a wind turbine

but goes in both directions

– Ceuires a daily tidal range

of /+> meters *1-/+&- feet,to be practical

– $haracteri:ed by low

capacity factors usually in

the range of &0+/I.


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Tidal Power

• ;ocations

– &'0 !W facility has operated in 8rance since

-G==

– &0 !W in $anada since -GF'

– # number of stations in $hina since -G>>

totaling / !W


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Tidal Power

• ;a Cance 8rance + world feet

– (am encloses F./ s. miles

– $apacity is &0000 MW


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Tidal Power

• ;ow Production but also ;ow

Environmental @mpact

– 3o no)ious waste

– 3o consumption of resources

– !inimum disturbance to scenery

tidal powerrrs

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