WAVES!!!
Draw me a picture of a perfect
surfing day!
No it doesn’t have to be a
Rembrandt or Monet just try!
Waves
Caused by:
• Wind
• Earthquakes
• Gravitational force of the Moon
and Sun.
Wave = an undulation of the water
surface, usually created by wind
• 1. crest = high point of a wave
• 2. trough = low point between two crests
• 3. wave height = height difference
between the trough and crest
• 4. wavelength = distance between two
crests
• 5. wave period = time taken for two crests
to pass a stationary object
A simple diagram… make sure you
have it in your notes
The wave period is a very useful
parameter in the classification of
waves
• Capillary waves =
small wind generated
waves that are most
readily seen on flat
calm water causes by
slight breezes and
local winds
• Wave period = <0.1
second
The wave period is a very useful
parameter in the classification of waves
• Chop = generated
locally these waves
are bigger than
capillary but relatively
small
• Wave period = 1 - 10
sec
The wave period is a very useful
parameter in the classification of
waves
• Swell = created by distant
storms wave lengths can
be up to hundreds of
meters do not necessarily
have large wave height
• Wave period = 10 - 30
sec
The wave period is a very useful
parameter in the classification of
waves
• Tsunami = created by
seismic activity
wavelength can be up
to hundreds of km,
can be very
distructive, known
previously as “Tidal
Wave”
• Wave period = 10 60 min
Believe it or not the water is staying
relatively still as a wave travels the
energy is moving.
• Wave energy travels in a circular path
• That energy cycle causes the water to rise
forming a crest
• And to fall causing a trough
Progressive waves = wind
generated waves
You can follow the crest of a
progressive wave across the
ocean, but what is really moving
is the energy!
Waves Caused by Wind
• When wind blows across a body
of water, friction causes the water
to move along with the wind.
• Wave Height depends on –
–Wind speed
–Distance over which the wind blows
–Length of time the wind blows
A steady wind of 56 mph is
blowing over an ocean and a
bathtub, are the same size
waves created in each? Why
or why not?
The type and size of wind generated
waves are dictated by 4 main factors
• 1. wind velocity = how fast the wind is traveling
• 2. wind duration = how long has the wind been
blowing
• 3. fetch = the area over of water over which the
wind is blowing
• 4. original sea state = how much wave action
already exists
•
a: “with old seas” = sea state originally had
waves and new ones are being added
•
b: “without old seas” = sea state was
originally without waves and new ones are being
added
The life of a wave
• fetch = the birthplace of waves, this is
where wind comes in contact with the
surface and transfers energy to the water,
causing waves
• higher wind speed creates higher and
longer waves (more powerful)
• waves formed by winds in the fetch are not
often well organized, they are chaotic and
mix of size and celerity
The speed of a wave is called
CELERITY
• Celerity = the speed of a wave, this term is used
because it is energy moving in a wave, not water
(mass)
• EX. Speed = time it takes a car to get down
the quarter mile D/T (mass has been
transported) D=distance T=time
• Celerity = time it takes the energy in a wave
to travel a distance L/T (no mass as moved)
L=wavelength T=wave period
Wave interference = interaction of
many waves
• Waves can either work to strengthen one an
other or to destroy each other
• Constructive interference = wave troughs and
crests coincide and create stronger waves
• Constructive wave interference can cause rogue
waves
• Rogue waves = unusually large waves that are
actually constructed of many coinciding smaller
waves
•
•
•
•
•
•
Fully developed sea = the waves have
grown to the largest size that the wind
speed will allow
Significant Wave Height = the average of
the highest third of all of the waves
The significant wave height will always be
more than the average of all
Think of your grades….
100, 100, 80, 75, 75, 50, 50, 50, 25
total average = 67.22
significant average = 93.33
Destructive wave interference = when the
trough of one wave meets up with the crest
of another, in effect reducing wave height
and length and period, making a weaker
wave
Dispersion = the wave organization
outside of the fetch area.
• Once waves leave an area of high winds no
more energy is being added and the wave
properties become stable
• (Think of the regularity of waves crashing on
the shore on a calm afternoon)
• longer waves having higher celerity will
separate from shorter waves and will reach
the shore faster than other weaker waves
Shallow water waves
• Shallow water wave = waves in water that
is 1/20th the wavelength
• Deep water wave cycles are unaffected by
the sea floor
Shallow water waves are changed
in three ways…
1. shallow water wave interference = waves can
“feel” the sea floor
• a. waves begin to loose celerity “speed” (the
celerity of all shallow water waves is determined
by depth)
• b. waves begin to slow and bunch up as the sea
floor saps their energy (waves travel slowest just
prior to breaking)
• c. wave height begins to grow as the wave
“pushes up on it’s self” (think about a crowd
trying to push through a small door)
• one thing that does NOT change…… WAVE
PERIOD….. this property of the wave still remains
constant
2. Shore breakers = waves that have
gotten into shallow enough water to cause
them to become unstable
• a. Spilling breaker = upper part of the crest
becomes too steep and spills or sweeps down
the front of the wave
• b. Plunging breaker = the crest of the wave
steepens curls over and plunges forward
• c. Surging breaker = the wave never really
“breaks” instead it rides up the beach smoothly
and retreats
Spilling Breaker
Plunging breaker
Tides
• The rise and fall in sea level is called
a tide.
• Caused by a giant wave.
• One low-tide/high-tide cycle takes
about 12 hrs and 25 min.
• Tidal range is the difference in ocean
level between high-tide and low-tide
What is the Tidal Range?
• HT = 30 ft, LT = 20 ft
• HT = 20 ft, LT = 12 ft
• HT = 50 ft, LT = 20 ft
Types of Tides
Spring: 1 st. and 3 rd. quarters
Neap: new and full moon
Gravitational Effect of the Moon
• Two big bulges of water form on
the Earth:
–one directly under the moon
–another on the exact opposite side
• As the Earth spins, the bulges
follow the moon.
Gravitational Effect of the Sun
• Spring Tides
–Earth, Moon, and Sun are lined up
–High Tides are higher and Low
Tides are lower than normal
Gravitational Effect of the Sun
• Neap Tides
–Earth, Moon, and Sun form right
angles
–High Tides are lower and Low Tides
are higher than normal
• St. Michel, N. coast of
France
• ~16.8 m highest tidal
range in Nova Scotia
Nova Scotia Tides
• Wolfville, NS (16 m tidal range)
• Diurnal Tides (one high and one low every 12
hours and 25 minutes